coverage: Always error on #[coverage(..)] in unexpected places

This upgrades some warnings to errors, and also catches cases where the
attribute was silently ignored.

Author: Zalathar

compiler/rustc_passes/messages.ftl

@@ -103,18 +103,9 @@ passes_continue_labeled_block =
 .label = labeled blocks cannot be `continue`'d
 .block_label = labeled block the `continue` points to
 
-passes_coverage_fn_defn =
- `#[coverage]` may only be applied to function definitions
-
-passes_coverage_ignored_function_prototype =
- `#[coverage]` is ignored on function prototypes
-
-passes_coverage_not_coverable =
- `#[coverage]` must be applied to coverable code
-.label = not coverable code
-
-passes_coverage_propagate =
- `#[coverage]` does not propagate into items and must be applied to the contained functions directly
+passes_coverage_not_fn_or_closure =
+ attribute should be applied to a function definition or closure
+.label = not a function or closure
 
 passes_dead_codes =
 {$multiple->

compiler/rustc_passes/src/check_attr.rs

@@ -122,7 +122,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
 self.check_diagnostic_on_unimplemented(attr.span, hir_id, target)
 }
 [sym::inline] => self.check_inline(hir_id, attr, span, target),
-[sym::coverage] => self.check_coverage(hir_id,attr, span, target),
+[sym::coverage] => self.check_coverage(attr, span, target),
 [sym::non_exhaustive] => self.check_non_exhaustive(hir_id, attr, span, target),
 [sym::marker] => self.check_marker(hir_id, attr, span, target),
 [sym::target_feature] => {
@@ -369,47 +369,15 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
 }
 }
 
-/// Checks if a `#[coverage]` is applied directly to a function
-fncheck_coverage(&self,hir_id:HirId,attr:&Attribute,span:Span,target:Target) -> bool{
+/// Checks that `#[coverage(..)]` is applied to a function or closure.
+fncheck_coverage(&self,attr:&Attribute,span:Span,target:Target) -> bool{
 match target {
-// #[coverage] on function is fine
+// #[coverage(..)] on function is fine
 Target::Fn
  | Target::Closure
  | Target::Method(MethodKind::Trait{body:true} | MethodKind::Inherent) => true,
-
-// function prototypes can't be covered
-Target::Method(MethodKind::Trait{body:false}) | Target::ForeignFn => {
-self.tcx.emit_node_span_lint(
-UNUSED_ATTRIBUTES,
- hir_id,
- attr.span,
- errors::IgnoredCoverageFnProto,
-);
-true
-}
-
-Target::Mod | Target::ForeignMod | Target::Impl | Target::Trait => {
-self.tcx.emit_node_span_lint(
-UNUSED_ATTRIBUTES,
- hir_id,
- attr.span,
- errors::IgnoredCoveragePropagate,
-);
-true
-}
-
-Target::Expression | Target::Statement | Target::Arm => {
-self.tcx.emit_node_span_lint(
-UNUSED_ATTRIBUTES,
- hir_id,
- attr.span,
- errors::IgnoredCoverageFnDefn,
-);
-true
-}
-
  _ => {
-self.dcx().emit_err(errors::IgnoredCoverageNotCoverable{
+self.dcx().emit_err(errors::CoverageNotFnOrClosure{
 attr_span: attr.span,
 defn_span: span,
 });

compiler/rustc_passes/src/errors.rs

@@ -60,21 +60,9 @@ pub struct InlineNotFnOrClosure {
 pubdefn_span:Span,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(passes_coverage_ignored_function_prototype)]
-pubstructIgnoredCoverageFnProto;
-
-#[derive(LintDiagnostic)]
-#[diag(passes_coverage_propagate)]
-pubstructIgnoredCoveragePropagate;
-
-#[derive(LintDiagnostic)]
-#[diag(passes_coverage_fn_defn)]
-pubstructIgnoredCoverageFnDefn;
-
 #[derive(Diagnostic)]
-#[diag(passes_coverage_not_coverable, code = E0788)]
-pubstructIgnoredCoverageNotCoverable{
+#[diag(passes_coverage_not_fn_or_closure, code = E0788)]
+pubstructCoverageNotFnOrClosure{
 #[primary_span]
 pubattr_span:Span,
 #[label]