Rollup merge of #128171 - compiler-errors:arg-compat, r=oli-obk

Make sure that args are compatible in `resolve_associated_item`

Implements a similar check to the one that we have in projection for GATs (#102488, #123240), where we check that the args of an impl item are compatible before returning it. This is done in `resolve_assoc_item`, which is backing `Instance::resolve`, so this is conceptually generalizing the check from GATs to methods/assoc consts. This is important to make sure that the inliner will only visit and substitute MIR bodies that are compatible w/ their trait definitions.

This shouldn't happen in codegen, but there are a few ways to get the inliner to be invoked (via calls to `optimized_mir`) before codegen, namely polymorphization and CTFE.

Fixes #121957
Fixes #120792
Fixes #120793
Fixes #121063

Author: matthiaskrgr

compiler/rustc_ty_utils/src/instance.rs

@@ -191,11 +191,22 @@ fn resolve_associated_item<'tcx>(
 
             // Any final impl is required to define all associated items.
             if !leaf_def.item.defaultness(tcx).has_value() {
-                let guard = tcx.dcx().span_delayed_bug(
+                let guar = tcx.dcx().span_delayed_bug(
                     tcx.def_span(leaf_def.item.def_id),
                     "missing value for assoc item in impl",
                 );
-                return Err(guard);
+                return Err(guar);
+            }
+
+            // Make sure that we're projecting to an item that has compatible args.
+            // This may happen if we are resolving an instance before codegen, such
+            // as during inlining. This check is also done in projection.
+            if !tcx.check_args_compatible(leaf_def.item.def_id, args) {
+                let guar = tcx.dcx().span_delayed_bug(
+                    tcx.def_span(leaf_def.item.def_id),
+                    "missing value for assoc item in impl",
+                );
+                return Err(guar);
             }
 
             let args = tcx.erase_regions(args);

tests/crashes/120792.rs

@@ -0,0 +1,27 @@
+// This test demonstrates an ICE that may occur when we try to resolve the instance
+// of a impl that has different generics than the trait it's implementing. This ensures
+// we first check that the args are compatible before resolving the body, just like
+// we do in projection before substituting a GAT.
+//
+// When polymorphization is enabled, we check the optimized MIR for unused parameters.
+// This will invoke the inliner, leading to this ICE.
+
+//@ compile-flags: -Zpolymorphize=on -Zinline-mir=yes
+
+trait Trait {
+    fn foo<'a, K: 'a>(self, _: K);
+}
+
+impl Trait for () {
+    #[inline]
+    fn foo<K>(self, _: K) {
+        //~^ ERROR lifetime parameters or bounds on method `foo` do not match the trait declaration
+        todo!();
+    }
+}
+
+pub fn qux<T>() {
+    ().foo(());
+}
+
+fn main() {}

tests/crashes/120793-2.rs

@@ -0,0 +1,15 @@
+error[E0195]: lifetime parameters or bounds on method `foo` do not match the trait declaration
+  --> $DIR/inline-incorrect-early-bound.rs:17:11
+   |
+LL |     fn foo<'a, K: 'a>(self, _: K);
+   |           -----------
+   |           |       |
+   |           |       this bound might be missing in the impl
+   |           lifetimes in impl do not match this method in trait
+...
+LL |     fn foo<K>(self, _: K) {
+   |           ^^^ lifetimes do not match method in trait
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0195`.

tests/crashes/120793.rs

@@ -0,0 +1,32 @@
+// This test demonstrates an ICE that may occur when we try to resolve the instance
+// of a impl that has different generics than the trait it's implementing. This ensures
+// we first check that the args are compatible before resolving the body, just like
+// we do in projection before substituting a GAT.
+//
+// Const traits aren't the only way to achieve this ICE, but it's a convenient way
+// to ensure the inliner is called.
+
+//@ compile-flags: -Znext-solver -Zinline-mir=yes
+
+#![feature(const_trait_impl, effects)]
+//~^ WARN the feature `effects` is incomplete
+
+trait Trait {
+    fn foo(self);
+}
+
+impl Trait for () {
+    #[inline]
+    fn foo<T>(self) {
+        //~^ ERROR  method `foo` has 1 type parameter but its trait declaration has 0 type parameters
+        todo!();
+    }
+}
+
+const fn foo() {
+    ().foo();
+}
+
+const UWU: () = foo();
+
+fn main() {}

tests/crashes/121063.rs

@@ -0,0 +1,21 @@
+warning: the feature `effects` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/inline-incorrect-early-bound-in-ctfe.rs:11:30
+   |
+LL | #![feature(const_trait_impl, effects)]
+   |                              ^^^^^^^
+   |
+   = note: see issue #102090 <https://github.com/rust-lang/rust/issues/102090> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0049]: method `foo` has 1 type parameter but its trait declaration has 0 type parameters
+  --> $DIR/inline-incorrect-early-bound-in-ctfe.rs:20:12
+   |
+LL |     fn foo(self);
+   |           - expected 0 type parameters
+...
+LL |     fn foo<T>(self) {
+   |            ^ found 1 type parameter
+
+error: aborting due to 1 previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0049`.