From d5bc71141da0fe2dd4b9a3d88bb1b1541c82a3a8 Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Sun, 11 Aug 2024 17:32:03 +0200
Subject: [PATCH 01/14] deps(rustc_expand): Add `rustc_middle` as a dep

---
 Cargo.lock                       | 1 +
 compiler/rustc_expand/Cargo.toml | 1 +
 2 files changed, 2 insertions(+)

diff --git a/Cargo.lock b/Cargo.lock
index 81aecf1cea77f..ddbe9a04ee9e6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3666,6 +3666,7 @@ dependencies = [
  "rustc_lexer",
  "rustc_lint_defs",
  "rustc_macros",
+ "rustc_middle",
  "rustc_parse",
  "rustc_serialize",
  "rustc_session",
diff --git a/compiler/rustc_expand/Cargo.toml b/compiler/rustc_expand/Cargo.toml
index ce014364b0d01..5e9092c84d074 100644
--- a/compiler/rustc_expand/Cargo.toml
+++ b/compiler/rustc_expand/Cargo.toml
@@ -20,6 +20,7 @@ rustc_fluent_macro = { path = "../rustc_fluent_macro" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_lint_defs = { path = "../rustc_lint_defs" }
 rustc_macros = { path = "../rustc_macros" }
+rustc_middle = { path = "../rustc_middle" }
 rustc_parse = { path = "../rustc_parse" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }

From de3349ce5db1bd47baf5b2bc7fb1201cb6104cfe Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Sun, 11 Aug 2024 17:32:29 +0200
Subject: [PATCH 02/14] refactor(rustc_expand): Take &SyntaxExtension instead
 of only &*Kind

---
 compiler/rustc_expand/src/expand.rs | 35 +++++++++++++++--------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index 0d56a005f159e..287cef732bb61 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -488,7 +488,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             self.cx.force_mode = force;
 
             let fragment_kind = invoc.fragment_kind;
-            match self.expand_invoc(invoc, &ext.kind) {
+            match self.expand_invoc(invoc, &ext) {
                 ExpandResult::Ready(fragment) => {
                     let mut derive_invocations = Vec::new();
                     let derive_placeholders = self
@@ -650,7 +650,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     fn expand_invoc(
         &mut self,
         invoc: Invocation,
-        ext: &SyntaxExtensionKind,
+        ext: &Lrc<SyntaxExtension>,
     ) -> ExpandResult<AstFragment, Invocation> {
         let recursion_limit = match self.cx.reduced_recursion_limit {
             Some((limit, _)) => limit,
@@ -671,7 +671,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
 
         let (fragment_kind, span) = (invoc.fragment_kind, invoc.span());
         ExpandResult::Ready(match invoc.kind {
-            InvocationKind::Bang { mac, span } => match ext {
+            InvocationKind::Bang { mac, span } => match &ext.kind {
                 SyntaxExtensionKind::Bang(expander) => {
                     match expander.expand(self.cx, span, mac.args.tokens.clone()) {
                         Ok(tok_result) => {
@@ -701,7 +701,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 }
                 _ => unreachable!(),
             },
-            InvocationKind::Attr { attr, pos, mut item, derives } => match ext {
+            InvocationKind::Attr { attr, pos, mut item, derives } => match &ext.kind {
                 SyntaxExtensionKind::Attr(expander) => {
                     self.gate_proc_macro_input(&item);
                     self.gate_proc_macro_attr_item(span, &item);
@@ -780,10 +780,10 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 }
                 _ => unreachable!(),
             },
-            InvocationKind::Derive { path, item, is_const } => match ext {
+            InvocationKind::Derive { path, item, is_const } => match &ext.kind {
                 SyntaxExtensionKind::Derive(expander)
                 | SyntaxExtensionKind::LegacyDerive(expander) => {
-                    if let SyntaxExtensionKind::Derive(..) = ext {
+                    if let SyntaxExtensionKind::Derive(..) = ext.kind {
                         self.gate_proc_macro_input(&item);
                     }
                     // The `MetaItem` representing the trait to derive can't
@@ -810,18 +810,19 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             },
             InvocationKind::GlobDelegation { item } => {
                 let AssocItemKind::DelegationMac(deleg) = &item.kind else { unreachable!() };
-                let suffixes = match ext {
-                    SyntaxExtensionKind::GlobDelegation(expander) => match expander.expand(self.cx)
-                    {
-                        ExpandResult::Ready(suffixes) => suffixes,
-                        ExpandResult::Retry(()) => {
-                            // Reassemble the original invocation for retrying.
-                            return ExpandResult::Retry(Invocation {
-                                kind: InvocationKind::GlobDelegation { item },
-                                ..invoc
-                            });
+                let suffixes = match &ext.kind {
+                    SyntaxExtensionKind::GlobDelegation(expander) => {
+                        match expander.expand(self.cx) {
+                            ExpandResult::Ready(suffixes) => suffixes,
+                            ExpandResult::Retry(()) => {
+                                // Reassemble the original invocation for retrying.
+                                return ExpandResult::Retry(Invocation {
+                                    kind: InvocationKind::GlobDelegation { item },
+                                    ..invoc
+                                });
+                            }
                         }
-                    },
+                    }
                     SyntaxExtensionKind::LegacyBang(..) => {
                         let msg = "expanded a dummy glob delegation";
                         let guar = self.cx.dcx().span_delayed_bug(span, msg);

From 461c7a77919d0b214cd9c69cbe43176aa674dc37 Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 03:24:07 +0200
Subject: [PATCH 03/14] wip: So yeah, tests pass, but still `eval_always` (not
 far from disk caching though I think)

---
 compiler/rustc_ast/src/tokenstream.rs         | 100 +++++++++++++++-
 compiler/rustc_expand/src/base.rs             |   3 +
 .../src/derive_macro_expansion.rs             | 113 ++++++++++++++++++
 compiler/rustc_expand/src/expand.rs           |   5 +
 compiler/rustc_expand/src/lib.rs              |   5 +
 compiler/rustc_expand/src/proc_macro.rs       |  48 ++++----
 compiler/rustc_interface/src/passes.rs        |   1 +
 compiler/rustc_middle/src/arena.rs            |   1 +
 compiler/rustc_middle/src/query/erase.rs      |   6 +
 compiler/rustc_middle/src/query/keys.rs       |  16 ++-
 compiler/rustc_middle/src/query/mod.rs        |   9 +-
 compiler/rustc_resolve/src/macros.rs          |   8 ++
 compiler/rustc_span/src/hygiene.rs            |   6 +
 13 files changed, 288 insertions(+), 33 deletions(-)
 create mode 100644 compiler/rustc_expand/src/derive_macro_expansion.rs

diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs
index fc1dd2caf681a..9eba534543541 100644
--- a/compiler/rustc_ast/src/tokenstream.rs
+++ b/compiler/rustc_ast/src/tokenstream.rs
@@ -14,12 +14,14 @@
 //! ownership of the original.
 
 use std::borrow::Cow;
+use std::hash::Hash;
 use std::{cmp, fmt, iter};
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::{self, Lrc};
 use rustc_macros::{Decodable, Encodable, HashStable_Generic};
-use rustc_serialize::{Decodable, Encodable};
+use rustc_serialize::{Decodable, Encodable, Encoder};
+use rustc_span::def_id::{CrateNum, DefIndex};
 use rustc_span::{sym, Span, SpanDecoder, SpanEncoder, Symbol, DUMMY_SP};
 
 use crate::ast::{AttrStyle, StmtKind};
@@ -139,8 +141,10 @@ impl fmt::Debug for LazyAttrTokenStream {
 }
 
 impl<S: SpanEncoder> Encodable<S> for LazyAttrTokenStream {
-    fn encode(&self, _s: &mut S) {
-        panic!("Attempted to encode LazyAttrTokenStream");
+    fn encode(&self, s: &mut S) {
+        // TODO: welp
+        // TODO: (also) `.flattened()` here?
+        self.to_attr_token_stream().encode(s)
     }
 }
 
@@ -296,6 +300,96 @@ pub struct AttrsTarget {
 #[derive(Clone, Debug, Default, Encodable, Decodable)]
 pub struct TokenStream(pub(crate) Lrc<Vec<TokenTree>>);
 
+struct HashEncoder<H: std::hash::Hasher> {
+    hasher: H,
+}
+
+impl<H: std::hash::Hasher> Encoder for HashEncoder<H> {
+    fn emit_usize(&mut self, v: usize) {
+        self.hasher.write_usize(v)
+    }
+
+    fn emit_u128(&mut self, v: u128) {
+        self.hasher.write_u128(v)
+    }
+
+    fn emit_u64(&mut self, v: u64) {
+        self.hasher.write_u64(v)
+    }
+
+    fn emit_u32(&mut self, v: u32) {
+        self.hasher.write_u32(v)
+    }
+
+    fn emit_u16(&mut self, v: u16) {
+        self.hasher.write_u16(v)
+    }
+
+    fn emit_u8(&mut self, v: u8) {
+        self.hasher.write_u8(v)
+    }
+
+    fn emit_isize(&mut self, v: isize) {
+        self.hasher.write_isize(v)
+    }
+
+    fn emit_i128(&mut self, v: i128) {
+        self.hasher.write_i128(v)
+    }
+
+    fn emit_i64(&mut self, v: i64) {
+        self.hasher.write_i64(v)
+    }
+
+    fn emit_i32(&mut self, v: i32) {
+        self.hasher.write_i32(v)
+    }
+
+    fn emit_i16(&mut self, v: i16) {
+        self.hasher.write_i16(v)
+    }
+
+    fn emit_raw_bytes(&mut self, s: &[u8]) {
+        self.hasher.write(s)
+    }
+}
+
+impl<H: std::hash::Hasher> SpanEncoder for HashEncoder<H> {
+    fn encode_span(&mut self, span: Span) {
+        span.hash(&mut self.hasher)
+    }
+
+    fn encode_symbol(&mut self, symbol: Symbol) {
+        symbol.hash(&mut self.hasher)
+    }
+
+    fn encode_expn_id(&mut self, expn_id: rustc_span::ExpnId) {
+        expn_id.hash(&mut self.hasher)
+    }
+
+    fn encode_syntax_context(&mut self, syntax_context: rustc_span::SyntaxContext) {
+        syntax_context.hash(&mut self.hasher)
+    }
+
+    fn encode_crate_num(&mut self, crate_num: CrateNum) {
+        crate_num.hash(&mut self.hasher)
+    }
+
+    fn encode_def_index(&mut self, def_index: DefIndex) {
+        def_index.hash(&mut self.hasher)
+    }
+
+    fn encode_def_id(&mut self, def_id: rustc_span::def_id::DefId) {
+        def_id.hash(&mut self.hasher)
+    }
+}
+
+impl Hash for TokenStream {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        Encodable::encode(self, &mut HashEncoder { hasher: state });
+    }
+}
+
 /// Indicates whether a token can join with the following token to form a
 /// compound token. Used for conversions to `proc_macro::Spacing`. Also used to
 /// guide pretty-printing, which is where the `JointHidden` value (which isn't
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 8f9104135cddd..736e98ed9ea1f 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -1072,6 +1072,9 @@ pub trait ResolverExpand {
         trait_def_id: DefId,
         impl_def_id: LocalDefId,
     ) -> Result<Vec<(Ident, Option<Ident>)>, Indeterminate>;
+
+    fn register_proc_macro_invoc(&mut self, invoc_id: LocalExpnId, ext: Lrc<SyntaxExtension>);
+    fn unregister_proc_macro_invoc(&mut self, invoc_id: LocalExpnId);
 }
 
 pub trait LintStoreExpand {
diff --git a/compiler/rustc_expand/src/derive_macro_expansion.rs b/compiler/rustc_expand/src/derive_macro_expansion.rs
new file mode 100644
index 0000000000000..ef58851a2e246
--- /dev/null
+++ b/compiler/rustc_expand/src/derive_macro_expansion.rs
@@ -0,0 +1,113 @@
+// TODO: remove
+#![allow(dead_code)]
+
+use std::cell::Cell;
+use std::ptr;
+
+use rustc_ast::tokenstream::TokenStream;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::profiling::SpannedEventArgRecorder;
+use rustc_span::LocalExpnId;
+
+use crate::base::ExtCtxt;
+use crate::errors;
+
+pub(super) fn expand<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    key: (LocalExpnId, &'tcx TokenStream),
+) -> Result<&'tcx TokenStream, ()> {
+    let (invoc_id, input) = key;
+
+    let res = with_context(|(ecx, client)| {
+        let span = invoc_id.expn_data().call_site;
+        let _timer =
+            ecx.sess.prof.generic_activity_with_arg_recorder("expand_proc_macro", |recorder| {
+                recorder.record_arg_with_span(ecx.sess.source_map(), ecx.expansion_descr(), span);
+            });
+        let proc_macro_backtrace = ecx.ecfg.proc_macro_backtrace;
+        let strategy = crate::proc_macro::exec_strategy(ecx);
+        let server = crate::proc_macro_server::Rustc::new(ecx);
+        let res = match client.run(&strategy, server, input.clone(), proc_macro_backtrace) {
+            // TODO: without flattened some (weird) tests fail, but no idea if it's correct/enough
+            Ok(stream) => Ok(tcx.arena.alloc(stream.flattened()) as &TokenStream),
+            Err(e) => {
+                ecx.dcx().emit_err({
+                    errors::ProcMacroDerivePanicked {
+                        span,
+                        message: e.as_str().map(|message| errors::ProcMacroDerivePanickedHelp {
+                            message: message.into(),
+                        }),
+                    }
+                });
+                Err(())
+            }
+        };
+        res
+    });
+
+    res
+}
+
+type CLIENT = pm::bridge::client::Client<pm::TokenStream, pm::TokenStream>;
+
+// based on rust/compiler/rustc_middle/src/ty/context/tls.rs
+// #[cfg(not(parallel_compiler))]
+thread_local! {
+    /// A thread local variable that stores a pointer to the current `CONTEXT`.
+    static TLV: Cell<(*mut (), Option<CLIENT>)> = const { Cell::new((ptr::null_mut(), None)) };
+}
+
+#[inline]
+fn erase(context: &mut ExtCtxt<'_>) -> *mut () {
+    context as *mut _ as *mut ()
+}
+
+#[inline]
+unsafe fn downcast<'a>(context: *mut ()) -> &'a mut ExtCtxt<'a> {
+    unsafe { &mut *(context as *mut ExtCtxt<'a>) }
+}
+
+/// Sets `context` as the new current `CONTEXT` for the duration of the function `f`.
+#[inline]
+pub fn enter_context<'a, F, R>(context: (&mut ExtCtxt<'a>, CLIENT), f: F) -> R
+where
+    F: FnOnce() -> R,
+{
+    let (ectx, client) = context;
+    let erased = (erase(ectx), Some(client));
+    TLV.with(|tlv| {
+        let old = tlv.replace(erased);
+        let _reset = rustc_data_structures::defer(move || tlv.set(old));
+        f()
+    })
+}
+
+/// Allows access to the current `CONTEXT` in a closure if one is available.
+#[inline]
+#[track_caller]
+pub fn with_context_opt<F, R>(f: F) -> R
+where
+    F: for<'a, 'b> FnOnce(Option<&'b mut (&mut ExtCtxt<'a>, CLIENT)>) -> R,
+{
+    let (ectx, client_opt) = TLV.get();
+    if ectx.is_null() {
+        f(None)
+    } else {
+        // We could get an `CONTEXT` pointer from another thread.
+        // Ensure that `CONTEXT` is `DynSync`.
+        // TODO: we should not be able to?
+        // sync::assert_dyn_sync::<CONTEXT<'_>>();
+
+        unsafe { f(Some(&mut (downcast(ectx), client_opt.unwrap()))) }
+    }
+}
+
+/// Allows access to the current `CONTEXT`.
+/// Panics if there is no `CONTEXT` available.
+#[inline]
+pub fn with_context<F, R>(f: F) -> R
+where
+    F: for<'a, 'b> FnOnce(&'b mut (&mut ExtCtxt<'a>, CLIENT)) -> R,
+{
+    with_context_opt(|opt_context| f(opt_context.expect("no CONTEXT stored in tls")))
+}
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index 287cef732bb61..d5d90a90ba29e 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -794,9 +794,14 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         span,
                         path,
                     };
+                    self.cx
+                        .resolver
+                        .register_proc_macro_invoc(invoc.expansion_data.id, ext.clone());
+                    invoc.expansion_data.id.expn_data();
                     let items = match expander.expand(self.cx, span, &meta, item, is_const) {
                         ExpandResult::Ready(items) => items,
                         ExpandResult::Retry(item) => {
+                            self.cx.resolver.unregister_proc_macro_invoc(invoc.expansion_data.id);
                             // Reassemble the original invocation for retrying.
                             return ExpandResult::Retry(Invocation {
                                 kind: InvocationKind::Derive { path: meta.path, item, is_const },
diff --git a/compiler/rustc_expand/src/lib.rs b/compiler/rustc_expand/src/lib.rs
index 777044e3f33bf..96e4677d7c5bb 100644
--- a/compiler/rustc_expand/src/lib.rs
+++ b/compiler/rustc_expand/src/lib.rs
@@ -29,10 +29,15 @@ mod proc_macro_server;
 pub use mbe::macro_rules::compile_declarative_macro;
 pub mod base;
 pub mod config;
+pub(crate) mod derive_macro_expansion;
 pub mod expand;
 pub mod module;
 // FIXME(Nilstrieb) Translate proc_macro diagnostics
 #[allow(rustc::untranslatable_diagnostic)]
 pub mod proc_macro;
 
+pub fn provide(providers: &mut rustc_middle::util::Providers) {
+    providers.derive_macro_expansion = derive_macro_expansion::expand;
+}
+
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
diff --git a/compiler/rustc_expand/src/proc_macro.rs b/compiler/rustc_expand/src/proc_macro.rs
index 24f631ed5dc98..d39d4582f84bf 100644
--- a/compiler/rustc_expand/src/proc_macro.rs
+++ b/compiler/rustc_expand/src/proc_macro.rs
@@ -2,6 +2,7 @@ use rustc_ast as ast;
 use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_errors::ErrorGuaranteed;
+use rustc_middle::ty;
 use rustc_parse::parser::{ForceCollect, Parser};
 use rustc_session::config::ProcMacroExecutionStrategy;
 use rustc_span::profiling::SpannedEventArgRecorder;
@@ -31,7 +32,7 @@ impl<T> pm::bridge::server::MessagePipe<T> for MessagePipe<T> {
     }
 }
 
-fn exec_strategy(ecx: &ExtCtxt<'_>) -> impl pm::bridge::server::ExecutionStrategy {
+pub fn exec_strategy(ecx: &ExtCtxt<'_>) -> impl pm::bridge::server::ExecutionStrategy {
     pm::bridge::server::MaybeCrossThread::<MessagePipe<_>>::new(
         ecx.sess.opts.unstable_opts.proc_macro_execution_strategy
             == ProcMacroExecutionStrategy::CrossThread,
@@ -124,36 +125,27 @@ impl MultiItemModifier for DeriveProcMacro {
         // altogether. See #73345.
         crate::base::ann_pretty_printing_compatibility_hack(&item, &ecx.sess);
         let input = item.to_tokens();
-        let stream = {
-            let _timer =
-                ecx.sess.prof.generic_activity_with_arg_recorder("expand_proc_macro", |recorder| {
-                    recorder.record_arg_with_span(
-                        ecx.sess.source_map(),
-                        ecx.expansion_descr(),
-                        span,
-                    );
-                });
-            let proc_macro_backtrace = ecx.ecfg.proc_macro_backtrace;
-            let strategy = exec_strategy(ecx);
-            let server = proc_macro_server::Rustc::new(ecx);
-            match self.client.run(&strategy, server, input, proc_macro_backtrace) {
-                Ok(stream) => stream,
-                Err(e) => {
-                    ecx.dcx().emit_err({
-                        errors::ProcMacroDerivePanicked {
-                            span,
-                            message: e.as_str().map(|message| {
-                                errors::ProcMacroDerivePanickedHelp { message: message.into() }
-                            }),
-                        }
-                    });
-                    return ExpandResult::Ready(vec![]);
-                }
-            }
+        let res = ty::tls::with(|tcx| {
+            // TODO: without flattened some (weird) tests fail, but no idea if it's correct/enough
+            let input = tcx.arena.alloc(input.flattened()) as &TokenStream;
+            let invoc_id = ecx.current_expansion.id;
+
+            assert_eq!(invoc_id.expn_data().call_site, span);
+
+            let res = crate::derive_macro_expansion::enter_context((ecx, self.client), move || {
+                let res = tcx.derive_macro_expansion((invoc_id, input)).cloned();
+                res
+            });
+
+            res
+        });
+        let Ok(output) = res else {
+            // error will already have been emitted
+            return ExpandResult::Ready(vec![]);
         };
 
         let error_count_before = ecx.dcx().err_count();
-        let mut parser = Parser::new(&ecx.sess.psess, stream, Some("proc-macro derive"));
+        let mut parser = Parser::new(&ecx.sess.psess, output, Some("proc-macro derive"));
         let mut items = vec![];
 
         loop {
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index c4a38047b5e3b..901d373fc11e4 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -624,6 +624,7 @@ pub static DEFAULT_QUERY_PROVIDERS: LazyLock<Providers> = LazyLock::new(|| {
     providers.resolutions = |tcx, ()| tcx.resolver_for_lowering_raw(()).1;
     providers.early_lint_checks = early_lint_checks;
     proc_macro_decls::provide(providers);
+    rustc_expand::provide(providers);
     rustc_const_eval::provide(providers);
     rustc_middle::hir::provide(providers);
     rustc_borrowck::provide(providers);
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 7050a06b8dc22..918ff15e70c55 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -114,6 +114,7 @@ macro_rules! arena_types {
             [decode] specialization_graph: rustc_middle::traits::specialization_graph::Graph,
             [] crate_inherent_impls: rustc_middle::ty::CrateInherentImpls,
             [] hir_owner_nodes: rustc_hir::OwnerNodes<'tcx>,
+            [] token_stream: rustc_ast::tokenstream::TokenStream,
         ]);
     )
 }
diff --git a/compiler/rustc_middle/src/query/erase.rs b/compiler/rustc_middle/src/query/erase.rs
index bd20e6aa00537..8476e937c7f3f 100644
--- a/compiler/rustc_middle/src/query/erase.rs
+++ b/compiler/rustc_middle/src/query/erase.rs
@@ -1,6 +1,8 @@
 use std::intrinsics::transmute_unchecked;
 use std::mem::MaybeUninit;
 
+use rustc_ast::tokenstream::TokenStream;
+
 use crate::query::CyclePlaceholder;
 use crate::ty::adjustment::CoerceUnsizedInfo;
 use crate::ty::{self, Ty};
@@ -172,6 +174,10 @@ impl EraseType for Result<ty::EarlyBinder<'_, Ty<'_>>, CyclePlaceholder> {
     type Result = [u8; size_of::<Result<ty::EarlyBinder<'static, Ty<'_>>, CyclePlaceholder>>()];
 }
 
+impl EraseType for Result<&'_ TokenStream, ()> {
+    type Result = [u8; size_of::<Result<&'static TokenStream, ()>>()];
+}
+
 impl<T> EraseType for Option<&'_ T> {
     type Result = [u8; size_of::<Option<&'static ()>>()];
 }
diff --git a/compiler/rustc_middle/src/query/keys.rs b/compiler/rustc_middle/src/query/keys.rs
index 6562d46d7b866..7d24f28169c87 100644
--- a/compiler/rustc_middle/src/query/keys.rs
+++ b/compiler/rustc_middle/src/query/keys.rs
@@ -1,10 +1,11 @@
 //! Defines the set of legal keys that can be used in queries.
 
+use rustc_ast::tokenstream::TokenStream;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LocalModDefId, ModDefId, LOCAL_CRATE};
 use rustc_hir::hir_id::{HirId, OwnerId};
 use rustc_query_system::query::{DefIdCache, DefaultCache, SingleCache, VecCache};
 use rustc_span::symbol::{Ident, Symbol};
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::{LocalExpnId, Span, DUMMY_SP};
 use rustc_target::abi;
 
 use crate::infer::canonical::Canonical;
@@ -575,6 +576,19 @@ impl Key for (LocalDefId, HirId) {
     }
 }
 
+impl<'tcx> Key for (LocalExpnId, &'tcx TokenStream) {
+    type Cache<V> = DefaultCache<Self, V>;
+
+    fn default_span(&self, _tcx: TyCtxt<'_>) -> Span {
+        self.0.expn_data().call_site
+    }
+
+    #[inline(always)]
+    fn key_as_def_id(&self) -> Option<DefId> {
+        None
+    }
+}
+
 impl<'tcx> Key for (ValidityRequirement, ty::ParamEnvAnd<'tcx, Ty<'tcx>>) {
     type Cache<V> = DefaultCache<Self, V>;
 
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 969374cb0e540..b11dd41624d35 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -14,6 +14,7 @@ use std::sync::Arc;
 use rustc_arena::TypedArena;
 use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_ast::expand::StrippedCfgItem;
+use rustc_ast::tokenstream::TokenStream;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::steal::Steal;
@@ -39,7 +40,7 @@ use rustc_session::lint::LintExpectationId;
 use rustc_session::Limits;
 use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::symbol::Symbol;
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::{LocalExpnId, Span, DUMMY_SP};
 use rustc_target::abi;
 use rustc_target::spec::PanicStrategy;
 use {rustc_ast as ast, rustc_attr as attr, rustc_hir as hir};
@@ -103,6 +104,12 @@ pub use plumbing::{IntoQueryParam, TyCtxtAt, TyCtxtEnsure, TyCtxtEnsureWithValue
 // Queries marked with `fatal_cycle` do not need the latter implementation,
 // as they will raise an fatal error on query cycles instead.
 rustc_queries! {
+    query derive_macro_expansion(key: (LocalExpnId, &'tcx TokenStream)) -> Result<&'tcx TokenStream, ()> {
+        eval_always
+        no_hash
+        desc { "expanding a derive (proc) macro" }
+    }
+
     /// This exists purely for testing the interactions between delayed bugs and incremental.
     query trigger_delayed_bug(key: DefId) {
         desc { "triggering a delayed bug for testing incremental" }
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 7203fbe4a0c18..8cce9a95bb57c 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -526,6 +526,14 @@ impl<'a, 'tcx> ResolverExpand for Resolver<'a, 'tcx> {
         });
         Ok(idents)
     }
+
+    fn register_proc_macro_invoc(&mut self, _invoc_id: LocalExpnId, _ext: Lrc<SyntaxExtension>) {
+        // TODO: dunno if need this yet
+    }
+
+    fn unregister_proc_macro_invoc(&mut self, _invoc_id: LocalExpnId) {
+        // TODO: dunno if need this yet
+    }
 }
 
 impl<'a, 'tcx> Resolver<'a, 'tcx> {
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index 463e0dbc30ce5..3ac842c2ca856 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -1572,3 +1572,9 @@ impl<CTX: HashStableContext> HashStable<CTX> for ExpnId {
         hash.hash_stable(ctx, hasher);
     }
 }
+
+impl<CTX: HashStableContext> HashStable<CTX> for LocalExpnId {
+    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
+        self.to_expn_id().hash_stable(hcx, hasher);
+    }
+}

From f2acfe5ac91da2ae75eac4350fcdc2afc4172587 Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 14:09:19 +0200
Subject: [PATCH 04/14] fix: Prevent double-enter with same `&mut ExtCtxt`
 (which would be UB)

---
 .../src/derive_macro_expansion.rs             | 26 ++++++++++++++-----
 compiler/rustc_expand/src/lib.rs              |  2 +-
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/compiler/rustc_expand/src/derive_macro_expansion.rs b/compiler/rustc_expand/src/derive_macro_expansion.rs
index ef58851a2e246..7a0535f6abdd0 100644
--- a/compiler/rustc_expand/src/derive_macro_expansion.rs
+++ b/compiler/rustc_expand/src/derive_macro_expansion.rs
@@ -12,7 +12,7 @@ use rustc_span::LocalExpnId;
 use crate::base::ExtCtxt;
 use crate::errors;
 
-pub(super) fn expand<'tcx>(
+pub(super) fn provide_derive_macro_expansion<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: (LocalExpnId, &'tcx TokenStream),
 ) -> Result<&'tcx TokenStream, ()> {
@@ -51,7 +51,6 @@ pub(super) fn expand<'tcx>(
 type CLIENT = pm::bridge::client::Client<pm::TokenStream, pm::TokenStream>;
 
 // based on rust/compiler/rustc_middle/src/ty/context/tls.rs
-// #[cfg(not(parallel_compiler))]
 thread_local! {
     /// A thread local variable that stores a pointer to the current `CONTEXT`.
     static TLV: Cell<(*mut (), Option<CLIENT>)> = const { Cell::new((ptr::null_mut(), None)) };
@@ -67,14 +66,11 @@ unsafe fn downcast<'a>(context: *mut ()) -> &'a mut ExtCtxt<'a> {
     unsafe { &mut *(context as *mut ExtCtxt<'a>) }
 }
 
-/// Sets `context` as the new current `CONTEXT` for the duration of the function `f`.
 #[inline]
-pub fn enter_context<'a, F, R>(context: (&mut ExtCtxt<'a>, CLIENT), f: F) -> R
+fn enter_context_erased<F, R>(erased: (*mut (), Option<CLIENT>), f: F) -> R
 where
     F: FnOnce() -> R,
 {
-    let (ectx, client) = context;
-    let erased = (erase(ectx), Some(client));
     TLV.with(|tlv| {
         let old = tlv.replace(erased);
         let _reset = rustc_data_structures::defer(move || tlv.set(old));
@@ -82,6 +78,17 @@ where
     })
 }
 
+/// Sets `context` as the new current `CONTEXT` for the duration of the function `f`.
+#[inline]
+pub fn enter_context<'a, F, R>(context: (&mut ExtCtxt<'a>, CLIENT), f: F) -> R
+where
+    F: FnOnce() -> R,
+{
+    let (ectx, client) = context;
+    let erased = (erase(ectx), Some(client));
+    enter_context_erased(erased, f)
+}
+
 /// Allows access to the current `CONTEXT` in a closure if one is available.
 #[inline]
 #[track_caller]
@@ -98,7 +105,12 @@ where
         // TODO: we should not be able to?
         // sync::assert_dyn_sync::<CONTEXT<'_>>();
 
-        unsafe { f(Some(&mut (downcast(ectx), client_opt.unwrap()))) }
+        // prevent double entering, as that would allow creating two `&mut ExtCtxt`s
+        // TODO: probably use a RefCell instead (which checks this properly)?
+        enter_context_erased((ptr::null_mut(), None), || unsafe {
+            let ectx = downcast(ectx);
+            f(Some(&mut (ectx, client_opt.unwrap())))
+        })
     }
 }
 
diff --git a/compiler/rustc_expand/src/lib.rs b/compiler/rustc_expand/src/lib.rs
index 96e4677d7c5bb..587784e7e5a87 100644
--- a/compiler/rustc_expand/src/lib.rs
+++ b/compiler/rustc_expand/src/lib.rs
@@ -37,7 +37,7 @@ pub mod module;
 pub mod proc_macro;
 
 pub fn provide(providers: &mut rustc_middle::util::Providers) {
-    providers.derive_macro_expansion = derive_macro_expansion::expand;
+    providers.derive_macro_expansion = derive_macro_expansion::provide_derive_macro_expansion;
 }
 
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }

From 7ff46763bbce6effb0f5a51423d6666017341b68 Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 14:11:41 +0200
Subject: [PATCH 05/14] chore: Remove old `allow`

---
 compiler/rustc_expand/src/derive_macro_expansion.rs | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/compiler/rustc_expand/src/derive_macro_expansion.rs b/compiler/rustc_expand/src/derive_macro_expansion.rs
index 7a0535f6abdd0..061765cb87733 100644
--- a/compiler/rustc_expand/src/derive_macro_expansion.rs
+++ b/compiler/rustc_expand/src/derive_macro_expansion.rs
@@ -1,6 +1,3 @@
-// TODO: remove
-#![allow(dead_code)]
-
 use std::cell::Cell;
 use std::ptr;
 

From 035d859bdcbf52d4eefd044a204ee6620e1ebcfb Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 14:48:43 +0200
Subject: [PATCH 06/14] chore: Remove unneeded code, adapt TODOs for pr-time

---
 compiler/rustc_ast/src/tokenstream.rs               | 4 ++--
 compiler/rustc_expand/src/base.rs                   | 3 ---
 compiler/rustc_expand/src/derive_macro_expansion.rs | 6 +++---
 compiler/rustc_expand/src/expand.rs                 | 4 ----
 compiler/rustc_expand/src/proc_macro.rs             | 2 +-
 compiler/rustc_resolve/src/macros.rs                | 8 --------
 6 files changed, 6 insertions(+), 21 deletions(-)

diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs
index 9eba534543541..620171a38cb9b 100644
--- a/compiler/rustc_ast/src/tokenstream.rs
+++ b/compiler/rustc_ast/src/tokenstream.rs
@@ -142,8 +142,8 @@ impl fmt::Debug for LazyAttrTokenStream {
 
 impl<S: SpanEncoder> Encodable<S> for LazyAttrTokenStream {
     fn encode(&self, s: &mut S) {
-        // TODO: welp
-        // TODO: (also) `.flattened()` here?
+        // TODO(pr-time): welp, do we really want this impl? maybe newtype wrapper?
+        // TODO(pr-time): (also) `.flattened()` here?
         self.to_attr_token_stream().encode(s)
     }
 }
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 736e98ed9ea1f..8f9104135cddd 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -1072,9 +1072,6 @@ pub trait ResolverExpand {
         trait_def_id: DefId,
         impl_def_id: LocalDefId,
     ) -> Result<Vec<(Ident, Option<Ident>)>, Indeterminate>;
-
-    fn register_proc_macro_invoc(&mut self, invoc_id: LocalExpnId, ext: Lrc<SyntaxExtension>);
-    fn unregister_proc_macro_invoc(&mut self, invoc_id: LocalExpnId);
 }
 
 pub trait LintStoreExpand {
diff --git a/compiler/rustc_expand/src/derive_macro_expansion.rs b/compiler/rustc_expand/src/derive_macro_expansion.rs
index 061765cb87733..2d79fca7a5d4e 100644
--- a/compiler/rustc_expand/src/derive_macro_expansion.rs
+++ b/compiler/rustc_expand/src/derive_macro_expansion.rs
@@ -25,7 +25,7 @@ pub(super) fn provide_derive_macro_expansion<'tcx>(
         let strategy = crate::proc_macro::exec_strategy(ecx);
         let server = crate::proc_macro_server::Rustc::new(ecx);
         let res = match client.run(&strategy, server, input.clone(), proc_macro_backtrace) {
-            // TODO: without flattened some (weird) tests fail, but no idea if it's correct/enough
+            // TODO(pr-time): without flattened some (weird) tests fail, but no idea if it's correct/enough
             Ok(stream) => Ok(tcx.arena.alloc(stream.flattened()) as &TokenStream),
             Err(e) => {
                 ecx.dcx().emit_err({
@@ -99,11 +99,11 @@ where
     } else {
         // We could get an `CONTEXT` pointer from another thread.
         // Ensure that `CONTEXT` is `DynSync`.
-        // TODO: we should not be able to?
+        // TODO(pr-time): we should not be able to?
         // sync::assert_dyn_sync::<CONTEXT<'_>>();
 
         // prevent double entering, as that would allow creating two `&mut ExtCtxt`s
-        // TODO: probably use a RefCell instead (which checks this properly)?
+        // TODO(pr-time): probably use a RefCell instead (which checks this properly)?
         enter_context_erased((ptr::null_mut(), None), || unsafe {
             let ectx = downcast(ectx);
             f(Some(&mut (ectx, client_opt.unwrap())))
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index d5d90a90ba29e..4da74befed4d9 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -794,14 +794,10 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         span,
                         path,
                     };
-                    self.cx
-                        .resolver
-                        .register_proc_macro_invoc(invoc.expansion_data.id, ext.clone());
                     invoc.expansion_data.id.expn_data();
                     let items = match expander.expand(self.cx, span, &meta, item, is_const) {
                         ExpandResult::Ready(items) => items,
                         ExpandResult::Retry(item) => {
-                            self.cx.resolver.unregister_proc_macro_invoc(invoc.expansion_data.id);
                             // Reassemble the original invocation for retrying.
                             return ExpandResult::Retry(Invocation {
                                 kind: InvocationKind::Derive { path: meta.path, item, is_const },
diff --git a/compiler/rustc_expand/src/proc_macro.rs b/compiler/rustc_expand/src/proc_macro.rs
index d39d4582f84bf..dfb67a35e1988 100644
--- a/compiler/rustc_expand/src/proc_macro.rs
+++ b/compiler/rustc_expand/src/proc_macro.rs
@@ -126,7 +126,7 @@ impl MultiItemModifier for DeriveProcMacro {
         crate::base::ann_pretty_printing_compatibility_hack(&item, &ecx.sess);
         let input = item.to_tokens();
         let res = ty::tls::with(|tcx| {
-            // TODO: without flattened some (weird) tests fail, but no idea if it's correct/enough
+            // TODO(pr-time): without flattened some (weird) tests fail, but no idea if it's correct/enough
             let input = tcx.arena.alloc(input.flattened()) as &TokenStream;
             let invoc_id = ecx.current_expansion.id;
 
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 8cce9a95bb57c..7203fbe4a0c18 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -526,14 +526,6 @@ impl<'a, 'tcx> ResolverExpand for Resolver<'a, 'tcx> {
         });
         Ok(idents)
     }
-
-    fn register_proc_macro_invoc(&mut self, _invoc_id: LocalExpnId, _ext: Lrc<SyntaxExtension>) {
-        // TODO: dunno if need this yet
-    }
-
-    fn unregister_proc_macro_invoc(&mut self, _invoc_id: LocalExpnId) {
-        // TODO: dunno if need this yet
-    }
 }
 
 impl<'a, 'tcx> Resolver<'a, 'tcx> {

From 7d6ce7736d8ba9ba73a96f95216e9ca062d79a6d Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 16:27:11 +0200
Subject: [PATCH 07/14] wip(test): Run with `-- --nocapture --verbose` and
 `invoked` should not appear in 2nd output

---
 .../auxiliary/derive_nothing.rs               | 24 ++++++++++
 .../derive_macro_expansion/item_changed.rs    | 48 +++++++++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 tests/incremental/derive_macro_expansion/auxiliary/derive_nothing.rs
 create mode 100644 tests/incremental/derive_macro_expansion/item_changed.rs

diff --git a/tests/incremental/derive_macro_expansion/auxiliary/derive_nothing.rs b/tests/incremental/derive_macro_expansion/auxiliary/derive_nothing.rs
new file mode 100644
index 0000000000000..cb572220aa197
--- /dev/null
+++ b/tests/incremental/derive_macro_expansion/auxiliary/derive_nothing.rs
@@ -0,0 +1,24 @@
+//@ force-host
+//@ no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro_derive(Nothing)]
+pub fn derive(input: TokenStream) -> TokenStream {
+    eprintln!("invoked");
+
+    r#"
+        pub mod nothing_mod {
+            // #[cfg(cfail1)]
+            pub fn nothing() {
+                eprintln!("nothing");
+            }
+
+            // #[cfg(cfail2)]
+            // fn nothingx() {}
+        }
+    "#.parse().unwrap()
+}
diff --git a/tests/incremental/derive_macro_expansion/item_changed.rs b/tests/incremental/derive_macro_expansion/item_changed.rs
new file mode 100644
index 0000000000000..c89a3d1c24d33
--- /dev/null
+++ b/tests/incremental/derive_macro_expansion/item_changed.rs
@@ -0,0 +1,48 @@
+//@ aux-build:derive_nothing.rs
+//@ revisions:cfail1 cfail2
+//@ compile-flags: -Z query-dep-graph
+//@ check-pass (FIXME(62277): could be check-pass?)
+
+// TODO(pr-time): do these revisions make sense? only "check" required?
+
+#![feature(rustc_attrs)]
+#![feature(stmt_expr_attributes)]
+#![allow(dead_code)]
+#![crate_type = "rlib"]
+
+#![rustc_partition_codegened(module="item_changed-foo", cfg="cfail1")]
+// #![rustc_partition_reused(module="item_changed-foo", cfg="cfail2")]
+#![rustc_partition_reused(module="item_changed-foo-nothing_mod", cfg="cfail2")]
+
+ #[macro_use]
+ extern crate derive_nothing;
+
+pub mod foo {
+    // #[rustc_clean(cfg="cfail2")]
+     #[derive(Nothing)]
+    pub struct Foo;
+
+    #[cfg(cfail2)]
+    pub fn second_fn() {
+        eprintln!("just forcing codegen");
+    }
+
+    pub fn use_foo(_f: Foo) {
+        // #[cfg(cfail1)]
+        nothing_mod::nothing();
+
+        // #[cfg(cfail2)]
+        // nothingx();
+
+        eprintln!("foo used");
+    }
+}
+
+// fn main() {
+//     Foo;
+//
+//     nothing();
+//
+//     #[cfg(rpass2)]
+//     Bar;
+// }

From 74dd64626ad8910276c60b21639f3bbf898b67da Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 18:20:49 +0200
Subject: [PATCH 08/14] wip: Activate, test (and fix) on_disk caching for
 proc-macro expansions!

Also add manual test.
---
 compiler/rustc_ast/src/tokenstream.rs         | 11 +++--
 .../src/derive_macro_expansion.rs             |  5 +-
 compiler/rustc_expand/src/proc_macro.rs       | 10 +++-
 compiler/rustc_middle/src/arena.rs            |  2 +-
 compiler/rustc_middle/src/query/keys.rs       |  3 +-
 compiler/rustc_middle/src/query/mod.rs        |  5 +-
 .../rustc_middle/src/query/on_disk_cache.rs   |  7 +++
 .../auxiliary/derive_nothing.rs               |  8 +---
 .../derive_macro_expansion/item_changed.rs    | 48 -------------------
 .../proc_macro_unchanged.rs                   | 37 ++++++++++++++
 10 files changed, 71 insertions(+), 65 deletions(-)
 delete mode 100644 tests/incremental/derive_macro_expansion/item_changed.rs
 create mode 100644 tests/incremental/derive_macro_expansion/proc_macro_unchanged.rs

diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs
index 620171a38cb9b..6909f5e090227 100644
--- a/compiler/rustc_ast/src/tokenstream.rs
+++ b/compiler/rustc_ast/src/tokenstream.rs
@@ -141,10 +141,13 @@ impl fmt::Debug for LazyAttrTokenStream {
 }
 
 impl<S: SpanEncoder> Encodable<S> for LazyAttrTokenStream {
-    fn encode(&self, s: &mut S) {
-        // TODO(pr-time): welp, do we really want this impl? maybe newtype wrapper?
-        // TODO(pr-time): (also) `.flattened()` here?
-        self.to_attr_token_stream().encode(s)
+    fn encode(&self, _s: &mut S) {
+        // TODO(pr-time): Just a reminder that this exists/was tried out,
+        // but probably not necessary anymore (see below).
+        // self.to_attr_token_stream().encode(s)
+        // We should not need to anymore, now that we `flatten`?
+        // Yep, that seems to be true! :)
+        panic!("Attempted to encode LazyAttrTokenStream");
     }
 }
 
diff --git a/compiler/rustc_expand/src/derive_macro_expansion.rs b/compiler/rustc_expand/src/derive_macro_expansion.rs
index 2d79fca7a5d4e..aa77e5a8ba4be 100644
--- a/compiler/rustc_expand/src/derive_macro_expansion.rs
+++ b/compiler/rustc_expand/src/derive_macro_expansion.rs
@@ -2,6 +2,7 @@ use std::cell::Cell;
 use std::ptr;
 
 use rustc_ast::tokenstream::TokenStream;
+use rustc_data_structures::svh::Svh;
 use rustc_middle::ty::TyCtxt;
 use rustc_span::profiling::SpannedEventArgRecorder;
 use rustc_span::LocalExpnId;
@@ -11,9 +12,9 @@ use crate::errors;
 
 pub(super) fn provide_derive_macro_expansion<'tcx>(
     tcx: TyCtxt<'tcx>,
-    key: (LocalExpnId, &'tcx TokenStream),
+    key: (LocalExpnId, Svh, &'tcx TokenStream),
 ) -> Result<&'tcx TokenStream, ()> {
-    let (invoc_id, input) = key;
+    let (invoc_id, _macro_crate_hash, input) = key;
 
     let res = with_context(|(ecx, client)| {
         let span = invoc_id.expn_data().call_site;
diff --git a/compiler/rustc_expand/src/proc_macro.rs b/compiler/rustc_expand/src/proc_macro.rs
index dfb67a35e1988..9e10b8cc72195 100644
--- a/compiler/rustc_expand/src/proc_macro.rs
+++ b/compiler/rustc_expand/src/proc_macro.rs
@@ -130,10 +130,18 @@ impl MultiItemModifier for DeriveProcMacro {
             let input = tcx.arena.alloc(input.flattened()) as &TokenStream;
             let invoc_id = ecx.current_expansion.id;
 
+            // TODO(pr-time): Just using the crate hash to notice when the proc-macro code has
+            // changed. How to *correctly* depend on exactly the macro definition?
+            // I.e., depending on the crate hash is just a HACK (and leaves garbage in the
+            // incremental compilation dir).
+            let macro_def_id = invoc_id.expn_data().macro_def_id.unwrap();
+            let proc_macro_crate_hash = tcx.crate_hash(macro_def_id.krate);
+
             assert_eq!(invoc_id.expn_data().call_site, span);
 
             let res = crate::derive_macro_expansion::enter_context((ecx, self.client), move || {
-                let res = tcx.derive_macro_expansion((invoc_id, input)).cloned();
+                let res =
+                    tcx.derive_macro_expansion((invoc_id, proc_macro_crate_hash, input)).cloned();
                 res
             });
 
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 918ff15e70c55..3a81f8f0167cf 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -114,7 +114,7 @@ macro_rules! arena_types {
             [decode] specialization_graph: rustc_middle::traits::specialization_graph::Graph,
             [] crate_inherent_impls: rustc_middle::ty::CrateInherentImpls,
             [] hir_owner_nodes: rustc_hir::OwnerNodes<'tcx>,
-            [] token_stream: rustc_ast::tokenstream::TokenStream,
+            [decode] token_stream: rustc_ast::tokenstream::TokenStream,
         ]);
     )
 }
diff --git a/compiler/rustc_middle/src/query/keys.rs b/compiler/rustc_middle/src/query/keys.rs
index 7d24f28169c87..470fe5ee69d80 100644
--- a/compiler/rustc_middle/src/query/keys.rs
+++ b/compiler/rustc_middle/src/query/keys.rs
@@ -1,6 +1,7 @@
 //! Defines the set of legal keys that can be used in queries.
 
 use rustc_ast::tokenstream::TokenStream;
+use rustc_data_structures::svh::Svh;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LocalModDefId, ModDefId, LOCAL_CRATE};
 use rustc_hir::hir_id::{HirId, OwnerId};
 use rustc_query_system::query::{DefIdCache, DefaultCache, SingleCache, VecCache};
@@ -576,7 +577,7 @@ impl Key for (LocalDefId, HirId) {
     }
 }
 
-impl<'tcx> Key for (LocalExpnId, &'tcx TokenStream) {
+impl<'tcx> Key for (LocalExpnId, Svh, &'tcx TokenStream) {
     type Cache<V> = DefaultCache<Self, V>;
 
     fn default_span(&self, _tcx: TyCtxt<'_>) -> Span {
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index b11dd41624d35..018e634696898 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -104,10 +104,11 @@ pub use plumbing::{IntoQueryParam, TyCtxtAt, TyCtxtEnsure, TyCtxtEnsureWithValue
 // Queries marked with `fatal_cycle` do not need the latter implementation,
 // as they will raise an fatal error on query cycles instead.
 rustc_queries! {
-    query derive_macro_expansion(key: (LocalExpnId, &'tcx TokenStream)) -> Result<&'tcx TokenStream, ()> {
-        eval_always
+    query derive_macro_expansion(key: (LocalExpnId, Svh, &'tcx TokenStream)) -> Result<&'tcx TokenStream, ()> {
+        // eval_always
         no_hash
         desc { "expanding a derive (proc) macro" }
+        cache_on_disk_if { true }
     }
 
     /// This exists purely for testing the interactions between delayed bugs and incremental.
diff --git a/compiler/rustc_middle/src/query/on_disk_cache.rs b/compiler/rustc_middle/src/query/on_disk_cache.rs
index ca52358218e92..da6bc33feaac0 100644
--- a/compiler/rustc_middle/src/query/on_disk_cache.rs
+++ b/compiler/rustc_middle/src/query/on_disk_cache.rs
@@ -790,6 +790,13 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>>
     }
 }
 
+impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx rustc_ast::tokenstream::TokenStream {
+    #[inline]
+    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Self {
+        RefDecodable::decode(d)
+    }
+}
+
 macro_rules! impl_ref_decoder {
     (<$tcx:tt> $($ty:ty,)*) => {
         $(impl<'a, $tcx> Decodable<CacheDecoder<'a, $tcx>> for &$tcx [$ty] {
diff --git a/tests/incremental/derive_macro_expansion/auxiliary/derive_nothing.rs b/tests/incremental/derive_macro_expansion/auxiliary/derive_nothing.rs
index cb572220aa197..a0fcadc463b8c 100644
--- a/tests/incremental/derive_macro_expansion/auxiliary/derive_nothing.rs
+++ b/tests/incremental/derive_macro_expansion/auxiliary/derive_nothing.rs
@@ -10,15 +10,11 @@ use proc_macro::TokenStream;
 pub fn derive(input: TokenStream) -> TokenStream {
     eprintln!("invoked");
 
-    r#"
+    return r#"
         pub mod nothing_mod {
-            // #[cfg(cfail1)]
             pub fn nothing() {
                 eprintln!("nothing");
             }
-
-            // #[cfg(cfail2)]
-            // fn nothingx() {}
         }
-    "#.parse().unwrap()
+    "#.parse().unwrap();
 }
diff --git a/tests/incremental/derive_macro_expansion/item_changed.rs b/tests/incremental/derive_macro_expansion/item_changed.rs
deleted file mode 100644
index c89a3d1c24d33..0000000000000
--- a/tests/incremental/derive_macro_expansion/item_changed.rs
+++ /dev/null
@@ -1,48 +0,0 @@
-//@ aux-build:derive_nothing.rs
-//@ revisions:cfail1 cfail2
-//@ compile-flags: -Z query-dep-graph
-//@ check-pass (FIXME(62277): could be check-pass?)
-
-// TODO(pr-time): do these revisions make sense? only "check" required?
-
-#![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
-#![allow(dead_code)]
-#![crate_type = "rlib"]
-
-#![rustc_partition_codegened(module="item_changed-foo", cfg="cfail1")]
-// #![rustc_partition_reused(module="item_changed-foo", cfg="cfail2")]
-#![rustc_partition_reused(module="item_changed-foo-nothing_mod", cfg="cfail2")]
-
- #[macro_use]
- extern crate derive_nothing;
-
-pub mod foo {
-    // #[rustc_clean(cfg="cfail2")]
-     #[derive(Nothing)]
-    pub struct Foo;
-
-    #[cfg(cfail2)]
-    pub fn second_fn() {
-        eprintln!("just forcing codegen");
-    }
-
-    pub fn use_foo(_f: Foo) {
-        // #[cfg(cfail1)]
-        nothing_mod::nothing();
-
-        // #[cfg(cfail2)]
-        // nothingx();
-
-        eprintln!("foo used");
-    }
-}
-
-// fn main() {
-//     Foo;
-//
-//     nothing();
-//
-//     #[cfg(rpass2)]
-//     Bar;
-// }
diff --git a/tests/incremental/derive_macro_expansion/proc_macro_unchanged.rs b/tests/incremental/derive_macro_expansion/proc_macro_unchanged.rs
new file mode 100644
index 0000000000000..151c9af29c2b5
--- /dev/null
+++ b/tests/incremental/derive_macro_expansion/proc_macro_unchanged.rs
@@ -0,0 +1,37 @@
+// This test tests that derive-macro execution is cached.
+// HOWEVER, this test can currently only be checked manually,
+// by running it (through compiletest) with `-- --nocapture --verbose`.
+// The proc-macro (for `Nothing`) prints a message to stderr when invoked,
+// and this message should only be present during the second invocation
+// (which has `cfail2` set via cfg).
+// TODO(pr-time): Properly have the test check this, but how? UI-test that tests for `.stderr`?
+
+//@ aux-build:derive_nothing.rs
+//@ revisions:cfail1 cfail2
+//@ compile-flags: -Z query-dep-graph
+//@ build-pass
+
+#![feature(rustc_attrs)]
+#![feature(stmt_expr_attributes)]
+#![allow(dead_code)]
+#![crate_type = "rlib"]
+
+#![rustc_partition_codegened(module="proc_macro_unchanged-foo", cfg="cfail1")]
+#![rustc_partition_codegened(module="proc_macro_unchanged-foo", cfg="cfail2")]
+
+// `foo::nothing_mod` is created by the derive macro and doesn't change
+#![rustc_partition_reused(module="proc_macro_unchanged-foo", cfg="cfail2")]
+
+ #[macro_use]
+ extern crate derive_nothing;
+
+pub mod foo {
+    #[derive(Nothing)]
+    pub struct Foo;
+
+    pub fn use_foo(_f: Foo) {
+        nothing_mod::nothing();
+
+        eprintln!("foo used");
+    }
+}

From 10657b6422ffefa0d4b687300285b29669ae0edd Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 22:23:18 +0200
Subject: [PATCH 09/14] chore: Adjust timing outputs

---
 compiler/rustc_expand/src/derive_macro_expansion.rs | 8 +++++---
 compiler/rustc_expand/src/proc_macro.rs             | 7 +++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_expand/src/derive_macro_expansion.rs b/compiler/rustc_expand/src/derive_macro_expansion.rs
index aa77e5a8ba4be..33349816f3afc 100644
--- a/compiler/rustc_expand/src/derive_macro_expansion.rs
+++ b/compiler/rustc_expand/src/derive_macro_expansion.rs
@@ -18,10 +18,12 @@ pub(super) fn provide_derive_macro_expansion<'tcx>(
 
     let res = with_context(|(ecx, client)| {
         let span = invoc_id.expn_data().call_site;
-        let _timer =
-            ecx.sess.prof.generic_activity_with_arg_recorder("expand_proc_macro", |recorder| {
+        let _timer = ecx.sess.prof.generic_activity_with_arg_recorder(
+            "expand_derive_proc_macro_inner",
+            |recorder| {
                 recorder.record_arg_with_span(ecx.sess.source_map(), ecx.expansion_descr(), span);
-            });
+            },
+        );
         let proc_macro_backtrace = ecx.ecfg.proc_macro_backtrace;
         let strategy = crate::proc_macro::exec_strategy(ecx);
         let server = crate::proc_macro_server::Rustc::new(ecx);
diff --git a/compiler/rustc_expand/src/proc_macro.rs b/compiler/rustc_expand/src/proc_macro.rs
index 9e10b8cc72195..055a306438d84 100644
--- a/compiler/rustc_expand/src/proc_macro.rs
+++ b/compiler/rustc_expand/src/proc_macro.rs
@@ -115,6 +115,13 @@ impl MultiItemModifier for DeriveProcMacro {
         item: Annotatable,
         _is_derive_const: bool,
     ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
+        let _timer = ecx.sess.prof.generic_activity_with_arg_recorder(
+            "expand_derive_proc_macro_outer",
+            |recorder| {
+                recorder.record_arg_with_span(ecx.sess.source_map(), ecx.expansion_descr(), span);
+            },
+        );
+
         // We need special handling for statement items
         // (e.g. `fn foo() { #[derive(Debug)] struct Bar; }`)
         let is_stmt = matches!(item, Annotatable::Stmt(..));

From 6296fcb27ca45163948d63ae7c5bdf9bf17bb0ab Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 22:23:39 +0200
Subject: [PATCH 10/14] feat: Add `-Zcache-all-derive-macros` to use/bypass
 cache

---
 compiler/rustc_expand/src/proc_macro.rs | 9 ++++++---
 compiler/rustc_session/src/options.rs   | 2 ++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_expand/src/proc_macro.rs b/compiler/rustc_expand/src/proc_macro.rs
index 055a306438d84..f22525c0ceedc 100644
--- a/compiler/rustc_expand/src/proc_macro.rs
+++ b/compiler/rustc_expand/src/proc_macro.rs
@@ -147,9 +147,12 @@ impl MultiItemModifier for DeriveProcMacro {
             assert_eq!(invoc_id.expn_data().call_site, span);
 
             let res = crate::derive_macro_expansion::enter_context((ecx, self.client), move || {
-                let res =
-                    tcx.derive_macro_expansion((invoc_id, proc_macro_crate_hash, input)).cloned();
-                res
+                let key = (invoc_id, proc_macro_crate_hash, input);
+                if tcx.sess.opts.unstable_opts.cache_all_derive_macros {
+                    tcx.derive_macro_expansion(key).cloned()
+                } else {
+                    crate::derive_macro_expansion::provide_derive_macro_expansion(tcx, key).cloned()
+                }
             });
 
             res
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index a57dc80b3168d..4e76241430beb 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1654,6 +1654,8 @@ options! {
         "emit noalias metadata for box (default: yes)"),
     branch_protection: Option<BranchProtection> = (None, parse_branch_protection, [TRACKED],
         "set options for branch target identification and pointer authentication on AArch64"),
+    cache_all_derive_macros: bool = (false, parse_bool, [UNTRACKED],
+        "cache the results of ALL derive macro invocations (potentially unsound!) (default: no)"),
     cf_protection: CFProtection = (CFProtection::None, parse_cfprotection, [TRACKED],
         "instrument control-flow architecture protection"),
     check_cfg_all_expected: bool = (false, parse_bool, [UNTRACKED],

From 14cb620ba3efe28d59e77f6415577291dce95734 Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 12 Aug 2024 23:43:41 +0200
Subject: [PATCH 11/14] wip: try also hashing query output

---
 compiler/rustc_middle/src/query/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 018e634696898..9e31ea726f82a 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -106,7 +106,7 @@ pub use plumbing::{IntoQueryParam, TyCtxtAt, TyCtxtEnsure, TyCtxtEnsureWithValue
 rustc_queries! {
     query derive_macro_expansion(key: (LocalExpnId, Svh, &'tcx TokenStream)) -> Result<&'tcx TokenStream, ()> {
         // eval_always
-        no_hash
+        // no_hash
         desc { "expanding a derive (proc) macro" }
         cache_on_disk_if { true }
     }

From ae181445b1d927eb73dbdbdf58a3c29c39dc1329 Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Wed, 14 Aug 2024 18:49:21 +0200
Subject: [PATCH 12/14] prepare for PR (tidy should pass, caching=yes by
 default for rustc-perf)

---
 compiler/rustc_ast/src/tokenstream.rs                       | 2 +-
 compiler/rustc_expand/src/derive_macro_expansion.rs         | 6 +++---
 compiler/rustc_expand/src/proc_macro.rs                     | 4 ++--
 compiler/rustc_session/src/options.rs                       | 4 ++--
 .../derive_macro_expansion/proc_macro_unchanged.rs          | 2 +-
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs
index 6909f5e090227..25479fabe8154 100644
--- a/compiler/rustc_ast/src/tokenstream.rs
+++ b/compiler/rustc_ast/src/tokenstream.rs
@@ -142,7 +142,7 @@ impl fmt::Debug for LazyAttrTokenStream {
 
 impl<S: SpanEncoder> Encodable<S> for LazyAttrTokenStream {
     fn encode(&self, _s: &mut S) {
-        // TODO(pr-time): Just a reminder that this exists/was tried out,
+        // FIXME(pr-time): Just a reminder that this exists/was tried out,
         // but probably not necessary anymore (see below).
         // self.to_attr_token_stream().encode(s)
         // We should not need to anymore, now that we `flatten`?
diff --git a/compiler/rustc_expand/src/derive_macro_expansion.rs b/compiler/rustc_expand/src/derive_macro_expansion.rs
index 33349816f3afc..9f1b95eb9cf91 100644
--- a/compiler/rustc_expand/src/derive_macro_expansion.rs
+++ b/compiler/rustc_expand/src/derive_macro_expansion.rs
@@ -28,7 +28,7 @@ pub(super) fn provide_derive_macro_expansion<'tcx>(
         let strategy = crate::proc_macro::exec_strategy(ecx);
         let server = crate::proc_macro_server::Rustc::new(ecx);
         let res = match client.run(&strategy, server, input.clone(), proc_macro_backtrace) {
-            // TODO(pr-time): without flattened some (weird) tests fail, but no idea if it's correct/enough
+            // FIXME(pr-time): without flattened some (weird) tests fail, but no idea if it's correct/enough
             Ok(stream) => Ok(tcx.arena.alloc(stream.flattened()) as &TokenStream),
             Err(e) => {
                 ecx.dcx().emit_err({
@@ -102,11 +102,11 @@ where
     } else {
         // We could get an `CONTEXT` pointer from another thread.
         // Ensure that `CONTEXT` is `DynSync`.
-        // TODO(pr-time): we should not be able to?
+        // FIXME(pr-time): we should not be able to?
         // sync::assert_dyn_sync::<CONTEXT<'_>>();
 
         // prevent double entering, as that would allow creating two `&mut ExtCtxt`s
-        // TODO(pr-time): probably use a RefCell instead (which checks this properly)?
+        // FIXME(pr-time): probably use a RefCell instead (which checks this properly)?
         enter_context_erased((ptr::null_mut(), None), || unsafe {
             let ectx = downcast(ectx);
             f(Some(&mut (ectx, client_opt.unwrap())))
diff --git a/compiler/rustc_expand/src/proc_macro.rs b/compiler/rustc_expand/src/proc_macro.rs
index f22525c0ceedc..69ce831361c33 100644
--- a/compiler/rustc_expand/src/proc_macro.rs
+++ b/compiler/rustc_expand/src/proc_macro.rs
@@ -133,11 +133,11 @@ impl MultiItemModifier for DeriveProcMacro {
         crate::base::ann_pretty_printing_compatibility_hack(&item, &ecx.sess);
         let input = item.to_tokens();
         let res = ty::tls::with(|tcx| {
-            // TODO(pr-time): without flattened some (weird) tests fail, but no idea if it's correct/enough
+            // FIXME(pr-time): without flattened some (weird) tests fail, but no idea if it's correct/enough
             let input = tcx.arena.alloc(input.flattened()) as &TokenStream;
             let invoc_id = ecx.current_expansion.id;
 
-            // TODO(pr-time): Just using the crate hash to notice when the proc-macro code has
+            // FIXME(pr-time): Just using the crate hash to notice when the proc-macro code has
             // changed. How to *correctly* depend on exactly the macro definition?
             // I.e., depending on the crate hash is just a HACK (and leaves garbage in the
             // incremental compilation dir).
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 4e76241430beb..14e188965497b 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1654,8 +1654,8 @@ options! {
         "emit noalias metadata for box (default: yes)"),
     branch_protection: Option<BranchProtection> = (None, parse_branch_protection, [TRACKED],
         "set options for branch target identification and pointer authentication on AArch64"),
-    cache_all_derive_macros: bool = (false, parse_bool, [UNTRACKED],
-        "cache the results of ALL derive macro invocations (potentially unsound!) (default: no)"),
+    cache_all_derive_macros: bool = (true, parse_bool, [UNTRACKED],
+        "cache the results of ALL derive macro invocations (potentially unsound!) (default: YES -- for rustc-perf)"),
     cf_protection: CFProtection = (CFProtection::None, parse_cfprotection, [TRACKED],
         "instrument control-flow architecture protection"),
     check_cfg_all_expected: bool = (false, parse_bool, [UNTRACKED],
diff --git a/tests/incremental/derive_macro_expansion/proc_macro_unchanged.rs b/tests/incremental/derive_macro_expansion/proc_macro_unchanged.rs
index 151c9af29c2b5..3b1505b171443 100644
--- a/tests/incremental/derive_macro_expansion/proc_macro_unchanged.rs
+++ b/tests/incremental/derive_macro_expansion/proc_macro_unchanged.rs
@@ -4,7 +4,7 @@
 // The proc-macro (for `Nothing`) prints a message to stderr when invoked,
 // and this message should only be present during the second invocation
 // (which has `cfail2` set via cfg).
-// TODO(pr-time): Properly have the test check this, but how? UI-test that tests for `.stderr`?
+// FIXME(pr-time): Properly have the test check this, but how? UI-test that tests for `.stderr`?
 
 //@ aux-build:derive_nothing.rs
 //@ revisions:cfail1 cfail2

From 55289311280831090db8e4cf4a2476fdb5cc9d6d Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 19 Aug 2024 14:53:04 +0200
Subject: [PATCH 13/14] wip: Undo unnecessary refactoring

---
 compiler/rustc_expand/src/expand.rs | 36 ++++++++++++++---------------
 1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index 4da74befed4d9..0d56a005f159e 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -488,7 +488,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             self.cx.force_mode = force;
 
             let fragment_kind = invoc.fragment_kind;
-            match self.expand_invoc(invoc, &ext) {
+            match self.expand_invoc(invoc, &ext.kind) {
                 ExpandResult::Ready(fragment) => {
                     let mut derive_invocations = Vec::new();
                     let derive_placeholders = self
@@ -650,7 +650,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     fn expand_invoc(
         &mut self,
         invoc: Invocation,
-        ext: &Lrc<SyntaxExtension>,
+        ext: &SyntaxExtensionKind,
     ) -> ExpandResult<AstFragment, Invocation> {
         let recursion_limit = match self.cx.reduced_recursion_limit {
             Some((limit, _)) => limit,
@@ -671,7 +671,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
 
         let (fragment_kind, span) = (invoc.fragment_kind, invoc.span());
         ExpandResult::Ready(match invoc.kind {
-            InvocationKind::Bang { mac, span } => match &ext.kind {
+            InvocationKind::Bang { mac, span } => match ext {
                 SyntaxExtensionKind::Bang(expander) => {
                     match expander.expand(self.cx, span, mac.args.tokens.clone()) {
                         Ok(tok_result) => {
@@ -701,7 +701,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 }
                 _ => unreachable!(),
             },
-            InvocationKind::Attr { attr, pos, mut item, derives } => match &ext.kind {
+            InvocationKind::Attr { attr, pos, mut item, derives } => match ext {
                 SyntaxExtensionKind::Attr(expander) => {
                     self.gate_proc_macro_input(&item);
                     self.gate_proc_macro_attr_item(span, &item);
@@ -780,10 +780,10 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 }
                 _ => unreachable!(),
             },
-            InvocationKind::Derive { path, item, is_const } => match &ext.kind {
+            InvocationKind::Derive { path, item, is_const } => match ext {
                 SyntaxExtensionKind::Derive(expander)
                 | SyntaxExtensionKind::LegacyDerive(expander) => {
-                    if let SyntaxExtensionKind::Derive(..) = ext.kind {
+                    if let SyntaxExtensionKind::Derive(..) = ext {
                         self.gate_proc_macro_input(&item);
                     }
                     // The `MetaItem` representing the trait to derive can't
@@ -794,7 +794,6 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         span,
                         path,
                     };
-                    invoc.expansion_data.id.expn_data();
                     let items = match expander.expand(self.cx, span, &meta, item, is_const) {
                         ExpandResult::Ready(items) => items,
                         ExpandResult::Retry(item) => {
@@ -811,19 +810,18 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             },
             InvocationKind::GlobDelegation { item } => {
                 let AssocItemKind::DelegationMac(deleg) = &item.kind else { unreachable!() };
-                let suffixes = match &ext.kind {
-                    SyntaxExtensionKind::GlobDelegation(expander) => {
-                        match expander.expand(self.cx) {
-                            ExpandResult::Ready(suffixes) => suffixes,
-                            ExpandResult::Retry(()) => {
-                                // Reassemble the original invocation for retrying.
-                                return ExpandResult::Retry(Invocation {
-                                    kind: InvocationKind::GlobDelegation { item },
-                                    ..invoc
-                                });
-                            }
+                let suffixes = match ext {
+                    SyntaxExtensionKind::GlobDelegation(expander) => match expander.expand(self.cx)
+                    {
+                        ExpandResult::Ready(suffixes) => suffixes,
+                        ExpandResult::Retry(()) => {
+                            // Reassemble the original invocation for retrying.
+                            return ExpandResult::Retry(Invocation {
+                                kind: InvocationKind::GlobDelegation { item },
+                                ..invoc
+                            });
                         }
-                    }
+                    },
                     SyntaxExtensionKind::LegacyBang(..) => {
                         let msg = "expanded a dummy glob delegation";
                         let guar = self.cx.dcx().span_delayed_bug(span, msg);

From 267a5c4518442c2028c8741d3230670b963712ba Mon Sep 17 00:00:00 2001
From: Felix Rath <felixm.rath@gmail.com>
Date: Mon, 9 Sep 2024 14:56:27 +0200
Subject: [PATCH 14/14] rebase + fix unreachable pub-items, inline some
 CONTEXT-things

---
 .../src/derive_macro_expansion.rs             | 75 +++++++------------
 compiler/rustc_expand/src/lib.rs              |  2 +-
 2 files changed, 27 insertions(+), 50 deletions(-)

diff --git a/compiler/rustc_expand/src/derive_macro_expansion.rs b/compiler/rustc_expand/src/derive_macro_expansion.rs
index 9f1b95eb9cf91..e93779819a967 100644
--- a/compiler/rustc_expand/src/derive_macro_expansion.rs
+++ b/compiler/rustc_expand/src/derive_macro_expansion.rs
@@ -1,5 +1,5 @@
 use std::cell::Cell;
-use std::ptr;
+use std::ptr::{self, NonNull};
 
 use rustc_ast::tokenstream::TokenStream;
 use rustc_data_structures::svh::Svh;
@@ -56,21 +56,14 @@ thread_local! {
     static TLV: Cell<(*mut (), Option<CLIENT>)> = const { Cell::new((ptr::null_mut(), None)) };
 }
 
+/// Sets `context` as the new current `CONTEXT` for the duration of the function `f`.
 #[inline]
-fn erase(context: &mut ExtCtxt<'_>) -> *mut () {
-    context as *mut _ as *mut ()
-}
-
-#[inline]
-unsafe fn downcast<'a>(context: *mut ()) -> &'a mut ExtCtxt<'a> {
-    unsafe { &mut *(context as *mut ExtCtxt<'a>) }
-}
-
-#[inline]
-fn enter_context_erased<F, R>(erased: (*mut (), Option<CLIENT>), f: F) -> R
+pub(crate) fn enter_context<'a, F, R>(context: (&mut ExtCtxt<'a>, CLIENT), f: F) -> R
 where
     F: FnOnce() -> R,
 {
+    let (ectx, client) = context;
+    let erased = (ectx as *mut _ as *mut (), Some(client));
     TLV.with(|tlv| {
         let old = tlv.replace(erased);
         let _reset = rustc_data_structures::defer(move || tlv.set(old));
@@ -78,48 +71,32 @@ where
     })
 }
 
-/// Sets `context` as the new current `CONTEXT` for the duration of the function `f`.
-#[inline]
-pub fn enter_context<'a, F, R>(context: (&mut ExtCtxt<'a>, CLIENT), f: F) -> R
-where
-    F: FnOnce() -> R,
-{
-    let (ectx, client) = context;
-    let erased = (erase(ectx), Some(client));
-    enter_context_erased(erased, f)
-}
-
-/// Allows access to the current `CONTEXT` in a closure if one is available.
+/// Allows access to the current `CONTEXT`.
+/// Panics if there is no `CONTEXT` available.
 #[inline]
 #[track_caller]
-pub fn with_context_opt<F, R>(f: F) -> R
+fn with_context<F, R>(f: F) -> R
 where
-    F: for<'a, 'b> FnOnce(Option<&'b mut (&mut ExtCtxt<'a>, CLIENT)>) -> R,
+    F: for<'a, 'b> FnOnce(&'b mut (&mut ExtCtxt<'a>, CLIENT)) -> R,
 {
     let (ectx, client_opt) = TLV.get();
-    if ectx.is_null() {
-        f(None)
-    } else {
-        // We could get an `CONTEXT` pointer from another thread.
-        // Ensure that `CONTEXT` is `DynSync`.
-        // FIXME(pr-time): we should not be able to?
-        // sync::assert_dyn_sync::<CONTEXT<'_>>();
+    let ectx = NonNull::new(ectx).expect("no CONTEXT stored in tls");
 
-        // prevent double entering, as that would allow creating two `&mut ExtCtxt`s
-        // FIXME(pr-time): probably use a RefCell instead (which checks this properly)?
-        enter_context_erased((ptr::null_mut(), None), || unsafe {
-            let ectx = downcast(ectx);
-            f(Some(&mut (ectx, client_opt.unwrap())))
-        })
-    }
-}
+    // We could get an `CONTEXT` pointer from another thread.
+    // Ensure that `CONTEXT` is `DynSync`.
+    // FIXME(pr-time): we should not be able to?
+    // sync::assert_dyn_sync::<CONTEXT<'_>>();
 
-/// Allows access to the current `CONTEXT`.
-/// Panics if there is no `CONTEXT` available.
-#[inline]
-pub fn with_context<F, R>(f: F) -> R
-where
-    F: for<'a, 'b> FnOnce(&'b mut (&mut ExtCtxt<'a>, CLIENT)) -> R,
-{
-    with_context_opt(|opt_context| f(opt_context.expect("no CONTEXT stored in tls")))
+    // prevent double entering, as that would allow creating two `&mut ExtCtxt`s
+    // FIXME(pr-time): probably use a RefCell instead (which checks this properly)?
+    TLV.with(|tlv| {
+        let old = tlv.replace((ptr::null_mut(), None));
+        let _reset = rustc_data_structures::defer(move || tlv.set(old));
+        let ectx = {
+            let mut casted = ectx.cast::<ExtCtxt<'_>>();
+            unsafe { casted.as_mut() }
+        };
+
+        f(&mut (ectx, client_opt.unwrap()))
+    })
 }
diff --git a/compiler/rustc_expand/src/lib.rs b/compiler/rustc_expand/src/lib.rs
index 587784e7e5a87..8f66605d705a6 100644
--- a/compiler/rustc_expand/src/lib.rs
+++ b/compiler/rustc_expand/src/lib.rs
@@ -29,7 +29,7 @@ mod proc_macro_server;
 pub use mbe::macro_rules::compile_declarative_macro;
 pub mod base;
 pub mod config;
-pub(crate) mod derive_macro_expansion;
+mod derive_macro_expansion;
 pub mod expand;
 pub mod module;
 // FIXME(Nilstrieb) Translate proc_macro diagnostics