Sort bounds by DefPathHash during astconv

cc #82920

The value of a `DefId` is not stable across compilation sessions. If we
sort by `DefIds`, and then include the sorted list as part of a query
result, then the query will no longer be a pure function of its input
(e.g. the `DefId` can change while the `DefPathHash` remains the same).

For reasons that are not yet clear, this issue lead to segfaults and
garbage slice index values when the project in the linked issue was
built with a particular incremental cache.

compiler/rustc_typeck/src/astconv/mod.rs

@@ -942,7 +942,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let mut bounds = Bounds::default();
 
         self.add_bounds(param_ty, ast_bounds, &mut bounds);
-        bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
+        // Sort by `DefPathHash` so that the order is stable across compilation sessions
+        bounds.trait_bounds.sort_by_key(|(t, _, _)| self.tcx().def_path_hash(t.def_id()));
 
         bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
             if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
@@ -1318,7 +1319,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
         // `dyn Trait + Send`.
-        auto_traits.sort_by_key(|i| i.trait_ref().def_id());
+        // Sort by `DefPathHash` so that the order is stable across compilation sessions
+        auto_traits.sort_by_key(|i| self.tcx().def_path_hash(i.trait_ref().def_id()));
         auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
         debug!("regular_traits: {:?}", regular_traits);
         debug!("auto_traits: {:?}", auto_traits);

src/test/ui/associated-type-bounds/bad-bounds-on-assoc-in-trait.stderr

@@ -10,38 +10,38 @@ help: consider further restricting the associated type
 LL | trait Case1 where <<Self as Case1>::C as Iterator>::Item: Iterator {
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0277]: `<<Self as Case1>::C as Iterator>::Item` cannot be sent between threads safely
-  --> $DIR/bad-bounds-on-assoc-in-trait.rs:27:36
+error[E0277]: `<<Self as Case1>::C as Iterator>::Item` cannot be shared between threads safely
+  --> $DIR/bad-bounds-on-assoc-in-trait.rs:27:93
    |
 LL |     type C: Clone + Iterator<Item: Send + Iterator<Item: for<'a> Lam<&'a u8, App: Debug>> + Sync>;
-   |                                    ^^^^ `<<Self as Case1>::C as Iterator>::Item` cannot be sent between threads safely
+   |                                                                                             ^^^^ `<<Self as Case1>::C as Iterator>::Item` cannot be shared between threads safely
    | 
   ::: $SRC_DIR/core/src/marker.rs:LL:COL
    |
-LL | pub unsafe auto trait Send {
-   | -------------------------- required by this bound in `Send`
+LL | pub unsafe auto trait Sync {
+   | -------------------------- required by this bound in `Sync`
    |
-   = help: the trait `Send` is not implemented for `<<Self as Case1>::C as Iterator>::Item`
+   = help: the trait `Sync` is not implemented for `<<Self as Case1>::C as Iterator>::Item`
 help: consider further restricting the associated type
    |
-LL | trait Case1 where <<Self as Case1>::C as Iterator>::Item: Send {
+LL | trait Case1 where <<Self as Case1>::C as Iterator>::Item: Sync {
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0277]: `<<Self as Case1>::C as Iterator>::Item` cannot be shared between threads safely
-  --> $DIR/bad-bounds-on-assoc-in-trait.rs:27:93
+error[E0277]: `<<Self as Case1>::C as Iterator>::Item` cannot be sent between threads safely
+  --> $DIR/bad-bounds-on-assoc-in-trait.rs:27:36
    |
 LL |     type C: Clone + Iterator<Item: Send + Iterator<Item: for<'a> Lam<&'a u8, App: Debug>> + Sync>;
-   |                                                                                             ^^^^ `<<Self as Case1>::C as Iterator>::Item` cannot be shared between threads safely
+   |                                    ^^^^ `<<Self as Case1>::C as Iterator>::Item` cannot be sent between threads safely
    | 
   ::: $SRC_DIR/core/src/marker.rs:LL:COL
    |
-LL | pub unsafe auto trait Sync {
-   | -------------------------- required by this bound in `Sync`
+LL | pub unsafe auto trait Send {
+   | -------------------------- required by this bound in `Send`
    |
-   = help: the trait `Sync` is not implemented for `<<Self as Case1>::C as Iterator>::Item`
+   = help: the trait `Send` is not implemented for `<<Self as Case1>::C as Iterator>::Item`
 help: consider further restricting the associated type
    |
-LL | trait Case1 where <<Self as Case1>::C as Iterator>::Item: Sync {
+LL | trait Case1 where <<Self as Case1>::C as Iterator>::Item: Send {
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 3 previous errors

src/test/ui/associated-types/defaults-unsound-62211-1.stderr

@@ -1,17 +1,16 @@
-error[E0277]: `Self` doesn't implement `std::fmt::Display`
+error[E0277]: the trait bound `Self: Copy` is not satisfied
   --> $DIR/defaults-unsound-62211-1.rs:20:5
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-------^^^^^^^^
-   |     |                                                                                |
-   |     |                                                                                required by this bound in `UncheckedCopy::Output`
-   |     `Self` cannot be formatted with the default formatter
+   |     ^^^^^^^^^^^^^----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     |            |
+   |     |            required by this bound in `UncheckedCopy::Output`
+   |     the trait `Copy` is not implemented for `Self`
    |
-   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 help: consider further restricting `Self`
    |
-LL | trait UncheckedCopy: Sized + std::fmt::Display {
-   |                            ^^^^^^^^^^^^^^^^^^^
+LL | trait UncheckedCopy: Sized + Copy {
+   |                            ^^^^^^
 
 error[E0277]: the trait bound `Self: Deref` is not satisfied
   --> $DIR/defaults-unsound-62211-1.rs:20:5
@@ -41,19 +40,20 @@ help: consider further restricting `Self`
 LL | trait UncheckedCopy: Sized + AddAssign<&'static str> {
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0277]: the trait bound `Self: Copy` is not satisfied
+error[E0277]: `Self` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-1.rs:20:5
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
-   |     ^^^^^^^^^^^^^----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |     |            |
-   |     |            required by this bound in `UncheckedCopy::Output`
-   |     the trait `Copy` is not implemented for `Self`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-------^^^^^^^^
+   |     |                                                                                |
+   |     |                                                                                required by this bound in `UncheckedCopy::Output`
+   |     `Self` cannot be formatted with the default formatter
    |
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 help: consider further restricting `Self`
    |
-LL | trait UncheckedCopy: Sized + Copy {
-   |                            ^^^^^^
+LL | trait UncheckedCopy: Sized + std::fmt::Display {
+   |                            ^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 4 previous errors
 

src/test/ui/associated-types/defaults-unsound-62211-2.stderr

@@ -1,17 +1,16 @@
-error[E0277]: `Self` doesn't implement `std::fmt::Display`
+error[E0277]: the trait bound `Self: Copy` is not satisfied
   --> $DIR/defaults-unsound-62211-2.rs:20:5
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-------^^^^^^^^
-   |     |                                                                                |
-   |     |                                                                                required by this bound in `UncheckedCopy::Output`
-   |     `Self` cannot be formatted with the default formatter
+   |     ^^^^^^^^^^^^^----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     |            |
+   |     |            required by this bound in `UncheckedCopy::Output`
+   |     the trait `Copy` is not implemented for `Self`
    |
-   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 help: consider further restricting `Self`
    |
-LL | trait UncheckedCopy: Sized + std::fmt::Display {
-   |                            ^^^^^^^^^^^^^^^^^^^
+LL | trait UncheckedCopy: Sized + Copy {
+   |                            ^^^^^^
 
 error[E0277]: the trait bound `Self: Deref` is not satisfied
   --> $DIR/defaults-unsound-62211-2.rs:20:5
@@ -41,19 +40,20 @@ help: consider further restricting `Self`
 LL | trait UncheckedCopy: Sized + AddAssign<&'static str> {
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0277]: the trait bound `Self: Copy` is not satisfied
+error[E0277]: `Self` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-2.rs:20:5
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
-   |     ^^^^^^^^^^^^^----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |     |            |
-   |     |            required by this bound in `UncheckedCopy::Output`
-   |     the trait `Copy` is not implemented for `Self`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-------^^^^^^^^
+   |     |                                                                                |
+   |     |                                                                                required by this bound in `UncheckedCopy::Output`
+   |     `Self` cannot be formatted with the default formatter
    |
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 help: consider further restricting `Self`
    |
-LL | trait UncheckedCopy: Sized + Copy {
-   |                            ^^^^^^
+LL | trait UncheckedCopy: Sized + std::fmt::Display {
+   |                            ^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 4 previous errors
 

src/test/ui/error-codes/E0225.stderr

@@ -13,17 +13,17 @@ error[E0225]: only auto traits can be used as additional traits in a trait objec
   --> $DIR/E0225.rs:8:20
    |
 LL | trait Foo = std::io::Read + std::io::Write;
-   |             -------------   -------------- additional non-auto trait
+   |             -------------   -------------- first non-auto trait
    |             |
-   |             first non-auto trait
+   |             additional non-auto trait
 ...
 LL |     let _: Box<dyn Foo>;
    |                    ^^^
    |                    |
    |                    trait alias used in trait object type (additional use)
    |                    trait alias used in trait object type (first use)
    |
-   = help: consider creating a new trait with all of these as super-traits and using that trait here instead: `trait NewTrait: std::io::Read + std::io::Write {}`
+   = help: consider creating a new trait with all of these as super-traits and using that trait here instead: `trait NewTrait: std::io::Write + std::io::Read {}`
    = note: auto-traits like `Send` and `Sync` are traits that have special properties; for more information on them, visit <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>
 
 error: aborting due to 2 previous errors

src/test/ui/issues/issue-40827.stderr

@@ -1,27 +1,27 @@
-error[E0277]: `Rc<Foo>` cannot be sent between threads safely
+error[E0277]: `Rc<Foo>` cannot be shared between threads safely
   --> $DIR/issue-40827.rs:14:5
    |
 LL | fn f<T: Send>(_: T) {}
    |         ---- required by this bound in `f`
 ...
 LL |     f(Foo(Arc::new(Bar::B(None))));
-   |     ^ `Rc<Foo>` cannot be sent between threads safely
+   |     ^ `Rc<Foo>` cannot be shared between threads safely
    |
-   = help: within `Bar`, the trait `Send` is not implemented for `Rc<Foo>`
+   = help: within `Bar`, the trait `Sync` is not implemented for `Rc<Foo>`
    = note: required because it appears within the type `Bar`
    = note: required because of the requirements on the impl of `Send` for `Arc<Bar>`
    = note: required because it appears within the type `Foo`
 
-error[E0277]: `Rc<Foo>` cannot be shared between threads safely
+error[E0277]: `Rc<Foo>` cannot be sent between threads safely
   --> $DIR/issue-40827.rs:14:5
    |
 LL | fn f<T: Send>(_: T) {}
    |         ---- required by this bound in `f`
 ...
 LL |     f(Foo(Arc::new(Bar::B(None))));
-   |     ^ `Rc<Foo>` cannot be shared between threads safely
+   |     ^ `Rc<Foo>` cannot be sent between threads safely
    |
-   = help: within `Bar`, the trait `Sync` is not implemented for `Rc<Foo>`
+   = help: within `Bar`, the trait `Send` is not implemented for `Rc<Foo>`
    = note: required because it appears within the type `Bar`
    = note: required because of the requirements on the impl of `Send` for `Arc<Bar>`
    = note: required because it appears within the type `Foo`

src/test/ui/suggestions/missing-trait-bounds-for-method-call.stderr

@@ -8,10 +8,10 @@ LL |         self.foo();
    |              ^^^ method cannot be called on `&Foo<T>` due to unsatisfied trait bounds
    |
    = note: the following trait bounds were not satisfied:
-           `T: Bar`
-           which is required by `Foo<T>: Bar`
            `T: Default`
            which is required by `Foo<T>: Bar`
+           `T: Bar`
+           which is required by `Foo<T>: Bar`
 help: consider restricting the type parameters to satisfy the trait bounds
    |
 LL | struct Foo<T> where T: Bar, T: Default {

src/test/ui/traits/alias/cross-crate.stderr

@@ -1,24 +1,24 @@
-error[E0277]: `Rc<u32>` cannot be sent between threads safely
+error[E0277]: `Rc<u32>` cannot be shared between threads safely
   --> $DIR/cross-crate.rs:14:17
    |
 LL | fn use_alias<T: SendSync>() {}
    |                 -------- required by this bound in `use_alias`
 ...
 LL |     use_alias::<Rc<u32>>();
-   |                 ^^^^^^^ `Rc<u32>` cannot be sent between threads safely
+   |                 ^^^^^^^ `Rc<u32>` cannot be shared between threads safely
    |
-   = help: the trait `Send` is not implemented for `Rc<u32>`
+   = help: the trait `Sync` is not implemented for `Rc<u32>`
 
-error[E0277]: `Rc<u32>` cannot be shared between threads safely
+error[E0277]: `Rc<u32>` cannot be sent between threads safely
   --> $DIR/cross-crate.rs:14:17
    |
 LL | fn use_alias<T: SendSync>() {}
    |                 -------- required by this bound in `use_alias`
 ...
 LL |     use_alias::<Rc<u32>>();
-   |                 ^^^^^^^ `Rc<u32>` cannot be shared between threads safely
+   |                 ^^^^^^^ `Rc<u32>` cannot be sent between threads safely
    |
-   = help: the trait `Sync` is not implemented for `Rc<u32>`
+   = help: the trait `Send` is not implemented for `Rc<u32>`
 
 error: aborting due to 2 previous errors
 

src/test/ui/traits/item-privacy.stderr

@@ -116,8 +116,8 @@ LL |     C::A;
    |     ^^^^ `assoc_const::C` cannot be made into an object
    |
    = help: consider moving `C` to another trait
-   = help: consider moving `B` to another trait
    = help: consider moving `A` to another trait
+   = help: consider moving `B` to another trait
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> $DIR/item-privacy.rs:25:15
    |