Auto merge of #127635 - matthiaskrgr:rollup-foopajr, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #127164 (match lowering: Clarify the main loop of the algorithm)
 - #127422 (as_simd: fix doc comment to be in line with align_to)
 - #127596 (More suggestion for converting `Option<&Vec<T>>` to `Option<&[T]>`)
 - #127607 (compiletest: Better error message for bad `normalize-*` headers)
 - #127622 (Mark `builtin_syntax` as internal)
 - #127625 (Revert accidental comment deletion)

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_borrowck/src/lib.rs

@@ -821,6 +821,8 @@ impl<'a, 'mir, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'mir, 'tcx, R>
             | TerminatorKind::Return
             | TerminatorKind::TailCall { .. }
             | TerminatorKind::CoroutineDrop => {
+                // Returning from the function implicitly kills storage for all locals and statics.
+                // Often, the storage will already have been killed by an explicit
                 // StorageDead, but we don't always emit those (notably on unwind paths),
                 // so this "extra check" serves as a kind of backup.
                 let borrow_set = self.borrow_set.clone();

compiler/rustc_feature/src/unstable.rs

@@ -248,6 +248,8 @@ declare_features! (
     (unstable, auto_traits, "1.50.0", Some(13231)),
     /// Allows using `box` in patterns (RFC 469).
     (unstable, box_patterns, "1.0.0", Some(29641)),
+    /// Allows builtin # foo() syntax
+    (internal, builtin_syntax, "1.71.0", Some(110680)),
     /// Allows `#[doc(notable_trait)]`.
     /// Renamed from `doc_spotlight`.
     (unstable, doc_notable_trait, "1.52.0", Some(45040)),
@@ -361,8 +363,6 @@ declare_features! (
     (unstable, async_fn_track_caller, "1.73.0", Some(110011)),
     /// Allows `for await` loops.
     (unstable, async_for_loop, "1.77.0", Some(118898)),
-    /// Allows builtin # foo() syntax
-    (unstable, builtin_syntax, "1.71.0", Some(110680)),
     /// Allows using C-variadics.
     (unstable, c_variadic, "1.34.0", Some(44930)),
     /// Allows the use of `#[cfg(overflow_checks)` to check if integer overflow behaviour.

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -466,21 +466,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     borrow_removal_span,
                 });
                 return true;
-            } else if let Some((deref_ty, _)) =
-                self.autoderef(expr.span, found_ty_inner).silence_errors().nth(1)
-                && self.can_eq(self.param_env, deref_ty, peeled)
-                && error_tys_equate_as_ref
-            {
-                let sugg = prefix_wrap(".as_deref()");
-                err.subdiagnostic(errors::SuggestConvertViaMethod {
-                    span: expr.span.shrink_to_hi(),
-                    sugg,
-                    expected,
-                    found,
-                    borrow_removal_span,
-                });
-                return true;
-            } else if let ty::Adt(adt, _) = found_ty_inner.peel_refs().kind()
+            } else if let ty::Ref(_, peeled_found_ty, _) = found_ty_inner.kind()
+                && let ty::Adt(adt, _) = peeled_found_ty.peel_refs().kind()
                 && self.tcx.is_lang_item(adt.did(), LangItem::String)
                 && peeled.is_str()
                 // `Result::map`, conversely, does not take ref of the error type.
@@ -496,12 +483,47 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     Applicability::MachineApplicable,
                 );
                 return true;
+            } else {
+                if !error_tys_equate_as_ref {
+                    return false;
+                }
+                let mut steps = self.autoderef(expr.span, found_ty_inner).silence_errors();
+                if let Some((deref_ty, _)) = steps.nth(1)
+                    && self.can_eq(self.param_env, deref_ty, peeled)
+                {
+                    let sugg = prefix_wrap(".as_deref()");
+                    err.subdiagnostic(errors::SuggestConvertViaMethod {
+                        span: expr.span.shrink_to_hi(),
+                        sugg,
+                        expected,
+                        found,
+                        borrow_removal_span,
+                    });
+                    return true;
+                }
+                for (deref_ty, n_step) in steps {
+                    if self.can_eq(self.param_env, deref_ty, peeled) {
+                        let explicit_deref = "*".repeat(n_step);
+                        let sugg = prefix_wrap(&format!(".map(|v| &{explicit_deref}v)"));
+                        err.subdiagnostic(errors::SuggestConvertViaMethod {
+                            span: expr.span.shrink_to_hi(),
+                            sugg,
+                            expected,
+                            found,
+                            borrow_removal_span,
+                        });
+                        return true;
+                    }
+                }
             }
         }
 
         false
     }
 
+    /// If `ty` is `Option<T>`, returns `T, T, None`.
+    /// If `ty` is `Result<T, E>`, returns `T, T, Some(E, E)`.
+    /// Otherwise, returns `None`.
     fn deconstruct_option_or_result(
         &self,
         found_ty: Ty<'tcx>,