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Improve error messages

This commit is contained in:
Ryan Levick 2021-01-12 14:58:51 +01:00 committed by Ryan Levick
parent 316e9db0cf
commit 49f32e0c8e
2 changed files with 25 additions and 21 deletions
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18
compiler/rustc_lint/src/noop_method_call.rs
View File

@ -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(&note)
.emit()
});
}

28
src/test/ui/lint/noop-method-call.stderr
View File

@ -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<u32> = 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<u32>` 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<u32> = 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<u32>` 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<u32> = 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<u32>` 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<u32>` 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