Rollup merge of #118419 - compiler-errors:await-span2, r=cjgillot

Eagerly return `ExprKind::Err` on `yield`/`await` in wrong coroutine context

This PR does 2 things:
1. Refuses to lower `.await` or `yield` when we are outside of the right coroutine context for the operator. Instead, we lower to `hir::ExprKind::Err`, to silence subsequent redundant errors.
2. Reworks a bit of the span tracking in `LoweringContext` to fix a bad span when we have something like `let x = [0; async_fn().await]` where the `await` is inside of an anon const. The span for the "item" still kinda sucks, since it overlaps with the `await` span, but at least it's accurate.

2 files changed, 4 insertions, 14 deletions

diff --git a/compiler/rustc_passes/src/check_const.rs b/compiler/rustc_passes/src/check_const.rs
index de96746e215..76c7467346d 100644
--- a/compiler/rustc_passes/src/check_const.rs
+++ b/compiler/rustc_passes/src/check_const.rs
@@ -17,7 +17,7 @@ use rustc_middle::ty::TyCtxt;
 use rustc_session::parse::feature_err;
 use rustc_span::{sym, Span, Symbol};
 
-use crate::errors::{ExprNotAllowedInContext, SkippingConstChecks};
+use crate::errors::SkippingConstChecks;
 
 /// An expression that is not *always* legal in a const context.
 #[derive(Clone, Copy)]
@@ -138,11 +138,10 @@ impl<'tcx> CheckConstVisitor<'tcx> {
 
         match missing_gates.as_slice() {
             [] => {
-                tcx.sess.emit_err(ExprNotAllowedInContext {
+                span_bug!(
                     span,
-                    expr: expr.name(),
-                    context: const_kind.keyword_name(),
-                });
+                    "we should not have reached this point, since `.await` is denied earlier"
+                );
             }
 
             [missing_primary, ref missing_secondary @ ..] => {
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index 411c9410195..58127445322 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -1005,15 +1005,6 @@ pub struct FeaturePreviouslyDeclared<'a, 'b> {
     pub prev_declared: &'b str,
 }
 
-#[derive(Diagnostic)]
-#[diag(passes_expr_not_allowed_in_context, code = "E0744")]
-pub struct ExprNotAllowedInContext<'a> {
-    #[primary_span]
-    pub span: Span,
-    pub expr: String,
-    pub context: &'a str,
-}
-
 pub struct BreakNonLoop<'a> {
     pub span: Span,
     pub head: Option<Span>,