From 49f32e0c8e78948210654299a8c19b2e0f0cbfa9 Mon Sep 17 00:00:00 2001 From: Ryan Levick Date: Tue, 12 Jan 2021 14:58:51 +0100 Subject: [PATCH] Improve error messages --- compiler/rustc_lint/src/noop_method_call.rs | 18 +++++++++---- src/test/ui/lint/noop-method-call.stderr | 28 +++++++++------------ 2 files changed, 25 insertions(+), 21 deletions(-) diff --git a/compiler/rustc_lint/src/noop_method_call.rs b/compiler/rustc_lint/src/noop_method_call.rs index e91dd37d8aa..1aa4a986cd1 100644 --- a/compiler/rustc_lint/src/noop_method_call.rs +++ b/compiler/rustc_lint/src/noop_method_call.rs @@ -39,7 +39,7 @@ declare_lint_pass!(NoopMethodCall => [NOOP_METHOD_CALL]); impl<'tcx> LateLintPass<'tcx> for NoopMethodCall { fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { // We only care about method calls - if let ExprKind::MethodCall(call, ..) = expr.kind { + if let ExprKind::MethodCall(call, _, elements, _) = expr.kind { // Get the `DefId` only when dealing with an `AssocFn` if let Some((DefKind::AssocFn, did)) = cx.typeck_results().type_dependent_def(expr.hir_id) @@ -70,15 +70,23 @@ impl<'tcx> LateLintPass<'tcx> for NoopMethodCall { .iter() .any(|s| cx.tcx.is_diagnostic_item(*s, i.def_id())) { + let method = &call.ident.name; + let receiver = &elements[0]; + let receiver_ty = cx.typeck_results().expr_ty(receiver); let expr_span = expr.span; + let note = format!( + "the type `{:?}` which `{}` is being called on is the same as the type returned from `{}`, \ + so the method call does not do anything and can be removed.", + receiver_ty, method, method + ); - cx.struct_span_lint(NOOP_METHOD_CALL, expr_span, |lint| { + let span = expr_span.with_lo(receiver.span.hi()); + cx.struct_span_lint(NOOP_METHOD_CALL, span, |lint| { let method = &call.ident.name; let message = format!("call to `.{}()` on a reference in this situation does nothing", &method); lint.build(&message) - .span_label(expr_span, "unnecessary method call") - .note("the type the method is being called on and the return type are functionally equivalent.") - .note("therefore, the method call doesn't actually do anything and can be removed.") + .span_label(span, "unnecessary method call") + .note(¬e) .emit() }); } diff --git a/src/test/ui/lint/noop-method-call.stderr b/src/test/ui/lint/noop-method-call.stderr index f9cc9735d54..7e27bf3abf9 100644 --- a/src/test/ui/lint/noop-method-call.stderr +++ b/src/test/ui/lint/noop-method-call.stderr @@ -1,39 +1,35 @@ warning: call to `.clone()` on a reference in this situation does nothing - --> $DIR/noop-method-call.rs:24:32 + --> $DIR/noop-method-call.rs:24:35 | LL | let foo_clone: &Foo = foo.clone(); - | ^^^^^^^^^^^ unnecessary method call + | ^^^^^^^^ unnecessary method call | = note: `#[warn(noop_method_call)]` on by default - = note: the type the method is being called on and the return type are functionally equivalent. - = note: therefore, the method call doesn't actually do anything and can be removed. + = note: the type `&Foo` which `clone` is being called on is the same as the type returned from `clone`, so the method call does not do anything and can be removed. warning: call to `.deref()` on a reference in this situation does nothing - --> $DIR/noop-method-call.rs:31:39 + --> $DIR/noop-method-call.rs:31:44 | LL | let derefed: &DerefExample = deref.deref(); - | ^^^^^^^^^^^^^ unnecessary method call + | ^^^^^^^^ unnecessary method call | - = note: the type the method is being called on and the return type are functionally equivalent. - = note: therefore, the method call doesn't actually do anything and can be removed. + = note: the type `&&DerefExample` which `deref` is being called on is the same as the type returned from `deref`, so the method call does not do anything and can be removed. warning: call to `.borrow()` on a reference in this situation does nothing - --> $DIR/noop-method-call.rs:38:31 + --> $DIR/noop-method-call.rs:38:32 | LL | let borrowed: &Foo = a.borrow(); - | ^^^^^^^^^^ unnecessary method call + | ^^^^^^^^^ unnecessary method call | - = note: the type the method is being called on and the return type are functionally equivalent. - = note: therefore, the method call doesn't actually do anything and can be removed. + = note: the type `&&Foo` which `borrow` is being called on is the same as the type returned from `borrow`, so the method call does not do anything and can be removed. warning: call to `.clone()` on a reference in this situation does nothing - --> $DIR/noop-method-call.rs:47:5 + --> $DIR/noop-method-call.rs:47:8 | LL | foo.clone(); - | ^^^^^^^^^^^ unnecessary method call + | ^^^^^^^^ unnecessary method call | - = note: the type the method is being called on and the return type are functionally equivalent. - = note: therefore, the method call doesn't actually do anything and can be removed. + = note: the type `&Foo` which `clone` is being called on is the same as the type returned from `clone`, so the method call does not do anything and can be removed. warning: 4 warnings emitted