Rollup merge of rust-lang#131024 - compiler-errors:deref-sugg, r=estebank

Don't give method suggestions when method probe fails due to bad implementation of `Deref`

If we have a bad `Deref` impl, we used to bail with `MethodError::NoMatch`, which makes the error reporting code think that there was no applicable method (and thus try to suggest importing something, even if it's in scope).

Suppress this error, which fixes rust-lang#131003.

Author: matthiaskrgr

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -18,8 +18,8 @@ use rustc_middle::ty::{
     self, GenericArgs, GenericArgsRef, GenericParamDefKind, Ty, TypeVisitableExt,
 };
 use rustc_middle::{bug, span_bug};
-use rustc_span::Span;
 use rustc_span::symbol::Ident;
+use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_trait_selection::traits::{self, NormalizeExt};
 use tracing::{debug, instrument};
@@ -46,26 +46,29 @@ pub(crate) struct MethodCallee<'tcx> {
 
 #[derive(Debug)]
 pub(crate) enum MethodError<'tcx> {
-    // Did not find an applicable method, but we did find various near-misses that may work.
+    /// Did not find an applicable method, but we did find various near-misses that may work.
     NoMatch(NoMatchData<'tcx>),
 
-    // Multiple methods might apply.
+    /// Multiple methods might apply.
     Ambiguity(Vec<CandidateSource>),
 
-    // Found an applicable method, but it is not visible. The third argument contains a list of
-    // not-in-scope traits which may work.
+    /// Found an applicable method, but it is not visible. The third argument contains a list of
+    /// not-in-scope traits which may work.
     PrivateMatch(DefKind, DefId, Vec<DefId>),
 
-    // Found a `Self: Sized` bound where `Self` is a trait object.
+    /// Found a `Self: Sized` bound where `Self` is a trait object.
     IllegalSizedBound {
         candidates: Vec<DefId>,
         needs_mut: bool,
         bound_span: Span,
         self_expr: &'tcx hir::Expr<'tcx>,
     },
 
-    // Found a match, but the return type is wrong
+    /// Found a match, but the return type is wrong
     BadReturnType,
+
+    /// Error has already been emitted, no need to emit another one.
+    ErrorReported(ErrorGuaranteed),
 }
 
 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
@@ -120,6 +123,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             Err(PrivateMatch(..)) => false,
             Err(IllegalSizedBound { .. }) => true,
             Err(BadReturnType) => false,
+            Err(ErrorReported(_)) => false,
         }
     }
 

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -446,13 +446,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     _ => bug!("unexpected bad final type in method autoderef"),
                 };
                 self.demand_eqtype(span, ty, Ty::new_error(self.tcx, guar));
-                return Err(MethodError::NoMatch(NoMatchData {
-                    static_candidates: Vec::new(),
-                    unsatisfied_predicates: Vec::new(),
-                    out_of_scope_traits: Vec::new(),
-                    similar_candidate: None,
-                    mode,
-                }));
+                return Err(MethodError::ErrorReported(guar));
             }
         }
 

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -229,20 +229,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         match error {
-            MethodError::NoMatch(mut no_match_data) => {
-                return self.report_no_match_method_error(
-                    span,
-                    rcvr_ty,
-                    item_name,
-                    call_id,
-                    source,
-                    args,
-                    sugg_span,
-                    &mut no_match_data,
-                    expected,
-                    trait_missing_method,
-                );
-            }
+            MethodError::NoMatch(mut no_match_data) => self.report_no_match_method_error(
+                span,
+                rcvr_ty,
+                item_name,
+                call_id,
+                source,
+                args,
+                sugg_span,
+                &mut no_match_data,
+                expected,
+                trait_missing_method,
+            ),
 
             MethodError::Ambiguity(mut sources) => {
                 let mut err = struct_span_code_err!(
@@ -263,7 +261,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     &mut sources,
                     Some(sugg_span),
                 );
-                return err.emit();
+                err.emit()
             }
 
             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
@@ -284,7 +282,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .unwrap_or_else(|| self.tcx.def_span(def_id));
                 err.span_label(sp, format!("private {kind} defined here"));
                 self.suggest_valid_traits(&mut err, item_name, out_of_scope_traits, true);
-                return err.emit();
+                err.emit()
             }
 
             MethodError::IllegalSizedBound { candidates, needs_mut, bound_span, self_expr } => {
@@ -383,9 +381,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         }
                     }
                 }
-                return err.emit();
+                err.emit()
             }
 
+            MethodError::ErrorReported(guar) => guar,
+
             MethodError::BadReturnType => bug!("no return type expectations but got BadReturnType"),
         }
     }

tests/ui/methods/dont-suggest-import-on-deref-err.rs

@@ -0,0 +1,13 @@
+use std::clone::Clone;
+use std::ops::Deref;
+
+#[derive(Clone)]
+pub struct Foo {}
+
+impl Deref for Foo {}
+//~^ ERROR not all trait items implemented
+
+pub fn main() {
+    let f = Foo {};
+    let _ = f.clone();
+}

tests/ui/methods/dont-suggest-import-on-deref-err.stderr

@@ -0,0 +1,12 @@
+error[E0046]: not all trait items implemented, missing: `Target`, `deref`
+  --> $DIR/dont-suggest-import-on-deref-err.rs:7:1
+   |
+LL | impl Deref for Foo {}
+   | ^^^^^^^^^^^^^^^^^^ missing `Target`, `deref` in implementation
+   |
+   = help: implement the missing item: `type Target = /* Type */;`
+   = help: implement the missing item: `fn deref(&self) -> &<Self as Deref>::Target { todo!() }`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0046`.