diff --git a/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs b/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs index 333ac0738d45b..0467bf76afecc 100644 --- a/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs +++ b/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs @@ -376,15 +376,18 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> { opt_assignment_rhs_span.and_then(|span| span.desugaring_kind()); match opt_desugaring_kind { // on for loops, RHS points to the iterator part - Some(DesugaringKind::ForLoop(_)) => Some(( - false, - opt_assignment_rhs_span.unwrap(), - format!( - "this iterator yields `{SIGIL}` {DESC}s", - SIGIL = pointer_sigil, - DESC = pointer_desc - ), - )), + Some(DesugaringKind::ForLoop(_)) => { + self.suggest_similar_mut_method_for_for_loop(&mut err); + Some(( + false, + opt_assignment_rhs_span.unwrap(), + format!( + "this iterator yields `{SIGIL}` {DESC}s", + SIGIL = pointer_sigil, + DESC = pointer_desc + ), + )) + } // don't create labels for compiler-generated spans Some(_) => None, None => { @@ -537,6 +540,79 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> { ); } + // Attempt to search similar mutable assosiated items for suggestion. + // In the future, attempt in all path but initially for RHS of for_loop + fn suggest_similar_mut_method_for_for_loop(&self, err: &mut DiagnosticBuilder<'_>) { + let hir = self.infcx.tcx.hir(); + let node = hir.item(self.mir_hir_id()); + use hir::{ + Expr, + ExprKind::{Block, Call, DropTemps, Match, MethodCall}, + }; + if let hir::ItemKind::Fn(_, _, body_id) = node.kind { + if let Block( + hir::Block { + expr: + Some(Expr { + kind: + DropTemps(Expr { + kind: + Match( + Expr { + kind: + Call( + _, + [Expr { + kind: MethodCall(path_segment, ..), + hir_id, + .. + }, ..], + ), + .. + }, + .., + ), + .. + }), + .. + }), + .. + }, + _, + ) = hir.body(body_id).value.kind + { + let opt_suggestions = path_segment + .hir_id + .map(|path_hir_id| self.infcx.tcx.typeck(path_hir_id.owner)) + .and_then(|typeck| typeck.type_dependent_def_id(*hir_id)) + .and_then(|def_id| self.infcx.tcx.impl_of_method(def_id)) + .map(|def_id| self.infcx.tcx.associated_items(def_id)) + .map(|assoc_items| { + assoc_items + .in_definition_order() + .map(|assoc_item_def| assoc_item_def.ident) + .filter(|&ident| { + let original_method_ident = path_segment.ident; + original_method_ident != ident + && ident + .as_str() + .starts_with(&original_method_ident.name.to_string()) + }) + .map(|ident| format!("{}()", ident)) + }); + + if let Some(suggestions) = opt_suggestions { + err.span_suggestions( + path_segment.ident.span, + &format!("use mutable method"), + suggestions, + Applicability::MaybeIncorrect, + ); + } + } + }; + } + /// Targeted error when encountering an `FnMut` closure where an `Fn` closure was expected. fn expected_fn_found_fn_mut_call(&self, err: &mut DiagnosticBuilder<'_>, sp: Span, act: &str) { err.span_label(sp, format!("cannot {}", act));