linker: Report linker flavors incompatible with the current target

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -23,7 +23,7 @@ use rustc_session::utils::NativeLibKind;
 use rustc_session::{filesearch, Session};
 use rustc_span::symbol::Symbol;
 use rustc_target::spec::crt_objects::{CrtObjects, LinkSelfContainedDefault};
-use rustc_target::spec::{Cc, LinkOutputKind, LinkerFlavor, LinkerFlavorCli, Lld, PanicStrategy};
+use rustc_target::spec::{Cc, LinkOutputKind, LinkerFlavor, Lld, PanicStrategy};
 use rustc_target::spec::{RelocModel, RelroLevel, SanitizerSet, SplitDebuginfo};
 
 use super::archive::{ArchiveBuilder, ArchiveBuilderBuilder};
@@ -1302,44 +1302,7 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
                 let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
                     sess.emit_fatal(errors::LinkerFileStem);
                 });
-
-                // Remove any version postfix.
-                let stem = stem
-                    .rsplit_once('-')
-                    .and_then(|(lhs, rhs)| rhs.chars().all(char::is_numeric).then_some(lhs))
-                    .unwrap_or(stem);
-
-                // GCC/Clang can have an optional target prefix.
-                let flavor = if stem == "emcc" {
-                    LinkerFlavor::EmCc
-                } else if stem == "gcc"
-                    || stem.ends_with("-gcc")
-                    || stem == "g++"
-                    || stem.ends_with("-g++")
-                    || stem == "clang"
-                    || stem.ends_with("-clang")
-                    || stem == "clang++"
-                    || stem.ends_with("-clang++")
-                {
-                    LinkerFlavor::from_cli(LinkerFlavorCli::Gcc, &sess.target)
-                } else if stem == "wasm-ld" || stem.ends_with("-wasm-ld") {
-                    LinkerFlavor::WasmLld(Cc::No)
-                } else if stem == "ld" || stem.ends_with("-ld") {
-                    LinkerFlavor::from_cli(LinkerFlavorCli::Ld, &sess.target)
-                } else if stem == "ld.lld" {
-                    LinkerFlavor::Gnu(Cc::No, Lld::Yes)
-                } else if stem == "link" {
-                    LinkerFlavor::Msvc(Lld::No)
-                } else if stem == "lld-link" {
-                    LinkerFlavor::Msvc(Lld::Yes)
-                } else if stem == "lld" || stem == "rust-lld" {
-                    let lld_flavor = sess.target.linker_flavor.lld_flavor();
-                    LinkerFlavor::from_cli(LinkerFlavorCli::Lld(lld_flavor), &sess.target)
-                } else {
-                    // fall back to the value in the target spec
-                    sess.target.linker_flavor
-                };
-
+                let flavor = sess.target.linker_flavor.with_linker_hints(stem);
                 Some((linker, flavor))
             }
             (None, None) => None,
@@ -1349,7 +1312,7 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
     // linker and linker flavor specified via command line have precedence over what the target
     // specification specifies
     let linker_flavor =
-        sess.opts.cg.linker_flavor.map(|flavor| LinkerFlavor::from_cli(flavor, &sess.target));
+        sess.opts.cg.linker_flavor.map(|flavor| sess.target.linker_flavor.with_cli_hints(flavor));
     if let Some(ret) = infer_from(sess, sess.opts.cg.linker.clone(), linker_flavor) {
         return ret;
     }

compiler/rustc_session/messages.ftl

@@ -27,6 +27,10 @@ session_feature_gate_error = {$explain}
 session_file_is_not_writeable = output file {$file} is not writeable -- check its permissions
 
 session_hexadecimal_float_literal_not_supported = hexadecimal float literal is not supported
+
+session_incompatible_linker_flavor = linker flavor `{$flavor}` is incompatible with the current target
+    .note = compatible flavors are: {$compatible_list}
+
 session_incorrect_cgu_reuse_type =
     CGU-reuse for `{$cgu_user_name}` is `{$actual_reuse}` but should be {$at_least ->
     [one] {"at least "}

compiler/rustc_session/src/config.rs

@@ -12,7 +12,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 
 use rustc_data_structures::stable_hasher::{StableOrd, ToStableHashKey};
 use rustc_target::abi::Align;
-use rustc_target::spec::{PanicStrategy, SanitizerSet, SplitDebuginfo};
+use rustc_target::spec::{LinkerFlavorCli, PanicStrategy, SanitizerSet, SplitDebuginfo};
 use rustc_target::spec::{Target, TargetTriple, TargetWarnings, TARGETS};
 
 use crate::parse::{CrateCheckConfig, CrateConfig};
@@ -2525,6 +2525,19 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         }
     }
 
+    if let Some(flavor) = cg.linker_flavor {
+        if matches!(flavor, LinkerFlavorCli::BpfLinker | LinkerFlavorCli::PtxLinker)
+            && !nightly_options::is_unstable_enabled(matches)
+        {
+            let msg = format!(
+                "linker flavor `{}` is unstable, `-Z unstable-options` \
+                 flag must also be passed to explicitly use it",
+                flavor.desc()
+            );
+            early_error(error_format, msg);
+        }
+    }
+
     let prints = collect_print_requests(&mut cg, &mut unstable_opts, matches, error_format);
 
     let cg = cg;

compiler/rustc_session/src/errors.rs

@@ -422,3 +422,11 @@ pub fn report_lit_error(sess: &ParseSess, err: LitError, lit: token::Lit, span:
 pub struct OptimisationFuelExhausted {
     pub msg: String,
 }
+
+#[derive(Diagnostic)]
+#[diag(session_incompatible_linker_flavor)]
+#[note]
+pub struct IncompatibleLinkerFlavor {
+    pub flavor: &'static str,
+    pub compatible_list: String,
+}

compiler/rustc_session/src/session.rs

@@ -1675,6 +1675,13 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
     if sess.opts.unstable_opts.instrument_xray.is_some() && !sess.target.options.supports_xray {
         sess.emit_err(errors::InstrumentationNotSupported { us: "XRay".to_string() });
     }
+
+    if let Some(flavor) = sess.opts.cg.linker_flavor {
+        if let Some(compatible_list) = sess.target.linker_flavor.check_compatibility(flavor) {
+            let flavor = flavor.desc();
+            sess.emit_err(errors::IncompatibleLinkerFlavor { flavor, compatible_list });
+        }
+    }
 }
 
 /// Holds data on the current incremental compilation session, if there is one.

compiler/rustc_target/src/lib.rs

@@ -11,6 +11,7 @@
 #![feature(assert_matches)]
 #![feature(associated_type_bounds)]
 #![feature(exhaustive_patterns)]
+#![feature(iter_intersperse)]
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]

compiler/rustc_target/src/spec/mod.rs

@@ -205,15 +205,11 @@ impl ToJson for LldFlavor {
 }
 
 impl LinkerFlavor {
-    pub fn from_cli(cli: LinkerFlavorCli, target: &TargetOptions) -> LinkerFlavor {
-        Self::from_cli_impl(cli, target.linker_flavor.lld_flavor(), target.linker_flavor.is_gnu())
-    }
-
-    /// The passed CLI flavor is preferred over other args coming from the default target spec,
-    /// so this function can produce a flavor that is incompatible with the current target.
-    /// FIXME: Produce errors when `-Clinker-flavor` is set to something incompatible
-    /// with the current target.
-    fn from_cli_impl(cli: LinkerFlavorCli, lld_flavor: LldFlavor, is_gnu: bool) -> LinkerFlavor {
+    /// At this point the target's reference linker flavor doesn't yet exist and we need to infer
+    /// it. The inference always succeds and gives some result, and we don't report any flavor
+    /// incompatibility errors for json target specs. The CLI flavor is used as the main source
+    /// of truth, other flags are used in case of ambiguities.
+    fn from_cli_json(cli: LinkerFlavorCli, lld_flavor: LldFlavor, is_gnu: bool) -> LinkerFlavor {
         match cli {
             LinkerFlavorCli::Gcc => match lld_flavor {
                 LldFlavor::Ld if is_gnu => LinkerFlavor::Gnu(Cc::Yes, Lld::No),
@@ -257,6 +253,85 @@ impl LinkerFlavor {
         }
     }
 
+    fn infer_cli_hints(cli: LinkerFlavorCli) -> (Option<Cc>, Option<Lld>) {
+        match cli {
+            LinkerFlavorCli::Gcc | LinkerFlavorCli::Em => (Some(Cc::Yes), None),
+            LinkerFlavorCli::Lld(_) => (Some(Cc::No), Some(Lld::Yes)),
+            LinkerFlavorCli::Ld | LinkerFlavorCli::Msvc => (Some(Cc::No), Some(Lld::No)),
+            LinkerFlavorCli::BpfLinker | LinkerFlavorCli::PtxLinker => (None, None),
+        }
+    }
+
+    fn infer_linker_hints(linker_stem: &str) -> (Option<Cc>, Option<Lld>) {
+        // Remove any version postfix.
+        let stem = linker_stem
+            .rsplit_once('-')
+            .and_then(|(lhs, rhs)| rhs.chars().all(char::is_numeric).then_some(lhs))
+            .unwrap_or(linker_stem);
+
+        // GCC/Clang can have an optional target prefix.
+        if stem == "emcc"
+            || stem == "gcc"
+            || stem.ends_with("-gcc")
+            || stem == "g++"
+            || stem.ends_with("-g++")
+            || stem == "clang"
+            || stem.ends_with("-clang")
+            || stem == "clang++"
+            || stem.ends_with("-clang++")
+        {
+            (Some(Cc::Yes), None)
+        } else if stem == "wasm-ld"
+            || stem.ends_with("-wasm-ld")
+            || stem == "ld.lld"
+            || stem == "lld"
+            || stem == "rust-lld"
+            || stem == "lld-link"
+        {
+            (Some(Cc::No), Some(Lld::Yes))
+        } else if stem == "ld" || stem.ends_with("-ld") || stem == "link" {
+            (Some(Cc::No), Some(Lld::No))
+        } else {
+            (None, None)
+        }
+    }
+
+    fn with_hints(self, (cc_hint, lld_hint): (Option<Cc>, Option<Lld>)) -> LinkerFlavor {
+        match self {
+            LinkerFlavor::Gnu(cc, lld) => {
+                LinkerFlavor::Gnu(cc_hint.unwrap_or(cc), lld_hint.unwrap_or(lld))
+            }
+            LinkerFlavor::Darwin(cc, lld) => {
+                LinkerFlavor::Darwin(cc_hint.unwrap_or(cc), lld_hint.unwrap_or(lld))
+            }
+            LinkerFlavor::WasmLld(cc) => LinkerFlavor::WasmLld(cc_hint.unwrap_or(cc)),
+            LinkerFlavor::Unix(cc) => LinkerFlavor::Unix(cc_hint.unwrap_or(cc)),
+            LinkerFlavor::Msvc(lld) => LinkerFlavor::Msvc(lld_hint.unwrap_or(lld)),
+            LinkerFlavor::EmCc | LinkerFlavor::Bpf | LinkerFlavor::Ptx => self,
+        }
+    }
+
+    pub fn with_cli_hints(self, cli: LinkerFlavorCli) -> LinkerFlavor {
+        self.with_hints(LinkerFlavor::infer_cli_hints(cli))
+    }
+
+    pub fn with_linker_hints(self, linker_stem: &str) -> LinkerFlavor {
+        self.with_hints(LinkerFlavor::infer_linker_hints(linker_stem))
+    }
+
+    pub fn check_compatibility(self, cli: LinkerFlavorCli) -> Option<String> {
+        // The CLI flavor should be compatible with the target if it survives this roundtrip.
+        let compatible = |cli| cli == self.with_cli_hints(cli).to_cli();
+        (!compatible(cli)).then(|| {
+            LinkerFlavorCli::all()
+                .iter()
+                .filter(|cli| compatible(**cli))
+                .map(|cli| cli.desc())
+                .intersperse(", ")
+                .collect()
+        })
+    }
+
     pub fn lld_flavor(self) -> LldFlavor {
         match self {
             LinkerFlavor::Gnu(..)
@@ -278,6 +353,10 @@ impl LinkerFlavor {
 macro_rules! linker_flavor_cli_impls {
     ($(($($flavor:tt)*) $string:literal)*) => (
         impl LinkerFlavorCli {
+            const fn all() -> &'static [LinkerFlavorCli] {
+                &[$($($flavor)*,)*]
+            }
+
             pub const fn one_of() -> &'static str {
                 concat!("one of: ", $($string, " ",)*)
             }
@@ -289,8 +368,8 @@ macro_rules! linker_flavor_cli_impls {
                 })
             }
 
-            pub fn desc(&self) -> &str {
-                match *self {
+            pub fn desc(self) -> &'static str {
+                match self {
                     $($($flavor)* => $string,)*
                 }
             }
@@ -1801,7 +1880,7 @@ impl TargetOptions {
     }
 
     fn update_from_cli(&mut self) {
-        self.linker_flavor = LinkerFlavor::from_cli_impl(
+        self.linker_flavor = LinkerFlavor::from_cli_json(
             self.linker_flavor_json,
             self.lld_flavor_json,
             self.linker_is_gnu_json,
@@ -1815,12 +1894,7 @@ impl TargetOptions {
         ] {
             args.clear();
             for (flavor, args_json) in args_json {
-                // Cannot use `from_cli` due to borrow checker.
-                let linker_flavor = LinkerFlavor::from_cli_impl(
-                    *flavor,
-                    self.lld_flavor_json,
-                    self.linker_is_gnu_json,
-                );
+                let linker_flavor = self.linker_flavor.with_cli_hints(*flavor);
                 // Normalize to no lld to avoid asserts.
                 let linker_flavor = match linker_flavor {
                     LinkerFlavor::Gnu(cc, _) => LinkerFlavor::Gnu(cc, Lld::No),

tests/ui/linkage-attr/incompatible-flavor.rs

@@ -0,0 +1,6 @@
+// compile-flags: --target=x86_64-unknown-linux-gnu -C linker-flavor=msvc --crate-type=rlib
+// error-pattern: linker flavor `msvc` is incompatible with the current target
+// needs-llvm-components:
+
+#![feature(no_core)]
+#![no_core]

tests/ui/linkage-attr/incompatible-flavor.stderr

@@ -0,0 +1,6 @@
+error: linker flavor `msvc` is incompatible with the current target
+   |
+   = note: compatible flavors are: gcc, ld, ld.lld
+
+error: aborting due to previous error
+

tests/ui/linkage-attr/issue-10755.rs

@@ -1,6 +1,6 @@
 // build-fail
 // dont-check-compiler-stderr
-// compile-flags: -C linker=llllll -C linker-flavor=ld
+// compile-flags: -C linker=llllll
 // error-pattern: `llllll`
 
 // Before, the error-pattern checked for "not found". On WSL with appendWindowsPath=true, running

tests/ui/linkage-attr/unstable-flavor.bpf.stderr

@@ -0,0 +1,2 @@
+error: linker flavor `bpf-linker` is unstable, `-Z unstable-options` flag must also be passed to explicitly use it
+

tests/ui/linkage-attr/unstable-flavor.ptx.stderr

@@ -0,0 +1,2 @@
+error: linker flavor `ptx-linker` is unstable, `-Z unstable-options` flag must also be passed to explicitly use it
+

tests/ui/linkage-attr/unstable-flavor.rs

@@ -0,0 +1,10 @@
+// revisions: bpf ptx
+// [bpf] compile-flags: --target=bpfel-unknown-none -C linker-flavor=bpf-linker --crate-type=rlib
+// [bpf] error-pattern: linker flavor `bpf-linker` is unstable, `-Z unstable-options` flag
+// [bpf] needs-llvm-components:
+// [ptx] compile-flags: --target=nvptx64-nvidia-cuda -C linker-flavor=ptx-linker --crate-type=rlib
+// [ptx] error-pattern: linker flavor `ptx-linker` is unstable, `-Z unstable-options` flag
+// [ptx] needs-llvm-components:
+
+#![feature(no_core)]
+#![no_core]