Fix ICE in normalizing inherent associated consts with #[type_const]

Author: lapla-cogito

compiler/rustc_trait_selection/src/traits/project.rs

@@ -586,7 +586,13 @@ pub fn compute_inherent_assoc_term_args<'a, 'b, 'tcx>(
 
     // Infer the generic parameters of the impl by unifying the
     // impl type with the self type of the projection.
-    let mut self_ty = alias_term.self_ty();
+    // For inherent associated consts, the args may not have a Self type at position 0.
+    // In that case, we use the impl_ty directly instead of calling self_ty().
+    let mut self_ty = if alias_term.args.is_empty() || alias_term.args[0].as_type().is_none() {
+        impl_ty
+    } else {
+        alias_term.self_ty()
+    };
     if !selcx.infcx.next_trait_solver() {
         self_ty = normalize_with_depth_to(
             selcx,

tests/ui/associated-types/type-const-inherent-impl-normalize.rs

@@ -0,0 +1,14 @@
+struct S<const N: usize>;
+impl<const N: usize> S<N> {
+    #[type_const]
+    //~^ ERROR: the `#[type_const]` attribute is an experimental feature
+    const LEN: usize = 1;
+    fn arr() {
+        [8; Self::LEN]
+        //~^ ERROR: constant expression depends on a generic parameter
+        //~| ERROR: constant expression depends on a generic parameter
+        //~| ERROR: mismatched types
+    }
+}
+
+pub fn main() {}

tests/ui/associated-types/type-const-inherent-impl-normalize.stderr

@@ -0,0 +1,38 @@
+error[E0658]: the `#[type_const]` attribute is an experimental feature
+  --> $DIR/type-const-inherent-impl-normalize.rs:3:5
+   |
+LL |     #[type_const]
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #132980 <https://github.com/rust-lang/rust/issues/132980> for more information
+   = help: add `#![feature(min_generic_const_args)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: constant expression depends on a generic parameter
+  --> $DIR/type-const-inherent-impl-normalize.rs:7:13
+   |
+LL |         [8; Self::LEN]
+   |             ^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
+error: constant expression depends on a generic parameter
+  --> $DIR/type-const-inherent-impl-normalize.rs:7:9
+   |
+LL |         [8; Self::LEN]
+   |         ^^^^^^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
+error[E0308]: mismatched types
+  --> $DIR/type-const-inherent-impl-normalize.rs:7:9
+   |
+LL |     fn arr() {
+   |             - help: try adding a return type: `-> [i32; Self::LEN]`
+LL |         [8; Self::LEN]
+   |         ^^^^^^^^^^^^^^ expected `()`, found `[{integer}; Self::LEN]`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0308, E0658.
+For more information about an error, try `rustc --explain E0308`.