typeck: Fix ICE for blocks in repeat expr count.

This commit extends the work in rust-lang#61698 to get the `DefId` of const
parameters from block that resolve to a const parameter (as well as
const parameters directly, as it was previously).

Author: davidtwco

src/librustc_typeck/astconv.rs

@@ -2157,6 +2157,14 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
 
     /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
     pub fn const_param_def_id(&self, expr: &hir::Expr) -> Option<DefId> {
+        // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
+        // currently have to be wrapped in curly brackets, so it's necessary to special-case.
+        let expr = match &expr.node {
+            ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() =>
+                block.expr.as_ref().unwrap(),
+            _ => expr,
+        };
+
         match &expr.node {
             ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
                 Res::Def(DefKind::ConstParam, did) => Some(did),
@@ -2184,18 +2192,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
             ty,
         };
 
-        let mut expr = &tcx.hir().body(ast_const.body).value;
-
-        // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
-        // currently have to be wrapped in curly brackets, so it's necessary to special-case.
-        if let ExprKind::Block(block, _) = &expr.node {
-            if block.stmts.is_empty() {
-                if let Some(trailing) = &block.expr {
-                    expr = &trailing;
-                }
-            }
-        }
-
+        let expr = &tcx.hir().body(ast_const.body).value;
         if let Some(def_id) = self.const_param_def_id(expr) {
             // Find the name and index of the const parameter by indexing the generics of the
             // parent item and construct a `ParamConst`.

src/test/ui/const-generics/issue-61336-2.rs

@@ -0,0 +1,16 @@
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+fn f<T: Copy, const N: usize>(x: T) -> [T; N] {
+    [x; {N}]
+}
+
+fn g<T, const N: usize>(x: T) -> [T; N] {
+    [x; {N}]
+    //~^ ERROR the trait bound `T: std::marker::Copy` is not satisfied [E0277]
+}
+
+fn main() {
+    let x: [u32; 5] = f::<u32, 5>(3);
+    assert_eq!(x, [3u32; 5]);
+}

src/test/ui/const-generics/issue-61336-2.stderr

@@ -0,0 +1,18 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-61336-2.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `T: std::marker::Copy` is not satisfied
+  --> $DIR/issue-61336-2.rs:9:5
+   |
+LL |     [x; {N}]
+   |     ^^^^^^^^ the trait `std::marker::Copy` is not implemented for `T`
+   |
+   = help: consider adding a `where T: std::marker::Copy` bound
+   = note: the `Copy` trait is required because the repeated element will be copied
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.