Rollup merge of #126682 - Zalathar:coverage-attr, r=lcnr

coverage: Overhaul validation of the `#[coverage(..)]` attribute

This PR makes sweeping changes to how the (currently-unstable) coverage attribute is validated:
- Multiple coverage attributes on the same item/expression are now treated as an error.
- The attribute must always be `#[coverage(off)]` or `#[coverage(on)]`, and the error messages for this are more consistent.
  -  A trailing comma is still allowed after off/on, since that's part of the normal attribute syntax.
- Some places that silently ignored a coverage attribute now produce an error instead.
  - These cases were all clearly bugs.
- Some places that ignored a coverage attribute (with a warning) now produce an error instead.
  - These were originally added as lints, but I don't think it makes much sense to knowingly allow new attributes to be used in meaningless places.
  - Some of these errors might soon disappear, if it's easy to extend recursive coverage attributes to things like modules and impl blocks.

---

One of the goals of this PR is to lay a more solid foundation for making the coverage attribute recursive, so that it applies to all nested functions/closures instead of just the one it is directly attached to.

Fixes #126658.

This PR incorporates #126659, which adds more tests for validation of the coverage attribute.

`@rustbot` label +A-code-coverage

compiler/rustc_codegen_ssa/messages.ftl

@@ -27,8 +27,6 @@ codegen_ssa_create_temp_dir = couldn't create a temp dir: {$error}
 
 codegen_ssa_error_creating_remark_dir = failed to create remark directory: {$error}
 
-codegen_ssa_expected_coverage_symbol = expected `coverage(off)` or `coverage(on)`
-
 codegen_ssa_expected_used_symbol = expected `used`, `used(compiler)` or `used(linker)`
 
 codegen_ssa_extern_funcs_not_found = some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -15,11 +15,7 @@ use rustc_span::{sym, Span};
 use rustc_target::spec::{abi, SanitizerSet};
 
 use crate::errors;
-use crate::target_features::from_target_feature;
-use crate::{
-    errors::{ExpectedCoverageSymbol, ExpectedUsedSymbol},
-    target_features::check_target_feature_trait_unsafe,
-};
+use crate::target_features::{check_target_feature_trait_unsafe, from_target_feature};
 
 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: LocalDefId, name: &str) -> Linkage {
     use rustc_middle::mir::mono::Linkage::*;
@@ -139,7 +135,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                         // coverage on a smaller scope within an excluded larger scope.
                     }
                     Some(_) | None => {
-                        tcx.dcx().emit_err(ExpectedCoverageSymbol { span: attr.span });
+                        tcx.dcx()
+                            .span_delayed_bug(attr.span, "unexpected value of coverage attribute");
                     }
                 }
             }
@@ -174,7 +171,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                         codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
                     }
                     Some(_) => {
-                        tcx.dcx().emit_err(ExpectedUsedSymbol { span: attr.span });
+                        tcx.dcx().emit_err(errors::ExpectedUsedSymbol { span: attr.span });
                     }
                     None => {
                         // Unfortunately, unconditionally using `llvm.used` causes

compiler/rustc_codegen_ssa/src/errors.rs

@@ -564,13 +564,6 @@ pub struct UnknownArchiveKind<'a> {
     pub kind: &'a str,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_expected_coverage_symbol)]
-pub struct ExpectedCoverageSymbol {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_expected_used_symbol)]
 pub struct ExpectedUsedSymbol {

compiler/rustc_feature/src/builtin_attrs.rs

@@ -105,6 +105,9 @@ pub struct AttributeTemplate {
     pub word: bool,
     /// If `Some`, the attribute is allowed to take a list of items like `#[allow(..)]`.
     pub list: Option<&'static str>,
+    /// If non-empty, the attribute is allowed to take a list containing exactly
+    /// one of the listed words, like `#[coverage(off)]`.
+    pub one_of: &'static [Symbol],
     /// If `Some`, the attribute is allowed to be a name/value pair where the
     /// value is a string, like `#[must_use = "reason"]`.
     pub name_value_str: Option<&'static str>,
@@ -165,19 +168,20 @@ pub enum AttributeDuplicates {
 /// E.g., `template!(Word, List: "description")` means that the attribute
 /// supports forms `#[attr]` and `#[attr(description)]`.
 macro_rules! template {
-    (Word) => { template!(@ true, None, None) };
-    (List: $descr: expr) => { template!(@ false, Some($descr), None) };
-    (NameValueStr: $descr: expr) => { template!(@ false, None, Some($descr)) };
-    (Word, List: $descr: expr) => { template!(@ true, Some($descr), None) };
-    (Word, NameValueStr: $descr: expr) => { template!(@ true, None, Some($descr)) };
+    (Word) => { template!(@ true, None, &[], None) };
+    (List: $descr: expr) => { template!(@ false, Some($descr), &[], None) };
+    (OneOf: $one_of: expr) => { template!(@ false, None, $one_of, None) };
+    (NameValueStr: $descr: expr) => { template!(@ false, None, &[], Some($descr)) };
+    (Word, List: $descr: expr) => { template!(@ true, Some($descr), &[], None) };
+    (Word, NameValueStr: $descr: expr) => { template!(@ true, None, &[], Some($descr)) };
     (List: $descr1: expr, NameValueStr: $descr2: expr) => {
-        template!(@ false, Some($descr1), Some($descr2))
+        template!(@ false, Some($descr1), &[], Some($descr2))
     };
     (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
-        template!(@ true, Some($descr1), Some($descr2))
+        template!(@ true, Some($descr1), &[], Some($descr2))
     };
-    (@ $word: expr, $list: expr, $name_value_str: expr) => { AttributeTemplate {
-        word: $word, list: $list, name_value_str: $name_value_str
+    (@ $word: expr, $list: expr, $one_of: expr, $name_value_str: expr) => { AttributeTemplate {
+        word: $word, list: $list, one_of: $one_of, name_value_str: $name_value_str
     } };
 }
 
@@ -478,8 +482,8 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::No, experimental!(no_sanitize)
     ),
     gated!(
-        coverage, Normal, template!(Word, List: "on|off"),
-        WarnFollowing, EncodeCrossCrate::No,
+        coverage, Normal, template!(OneOf: &[sym::off, sym::on]),
+        ErrorPreceding, EncodeCrossCrate::No,
         coverage_attribute, experimental!(coverage)
     ),
 

compiler/rustc_parse/src/validate_attr.rs

@@ -4,8 +4,10 @@ use crate::{errors, parse_in};
 
 use rustc_ast::token::Delimiter;
 use rustc_ast::tokenstream::DelimSpan;
-use rustc_ast::MetaItemKind;
-use rustc_ast::{self as ast, AttrArgs, AttrArgsEq, Attribute, DelimArgs, MetaItem, Safety};
+use rustc_ast::{
+    self as ast, AttrArgs, AttrArgsEq, Attribute, DelimArgs, MetaItem, MetaItemKind,
+    NestedMetaItem, Safety,
+};
 use rustc_errors::{Applicability, FatalError, PResult};
 use rustc_feature::{
     AttributeSafety, AttributeTemplate, BuiltinAttribute, Features, BUILTIN_ATTRIBUTE_MAP,
@@ -184,9 +186,13 @@ pub(super) fn check_cfg_attr_bad_delim(psess: &ParseSess, span: DelimSpan, delim
 
 /// Checks that the given meta-item is compatible with this `AttributeTemplate`.
 fn is_attr_template_compatible(template: &AttributeTemplate, meta: &ast::MetaItemKind) -> bool {
+    let is_one_allowed_subword = |items: &[NestedMetaItem]| match items {
+        [item] => item.is_word() && template.one_of.iter().any(|&word| item.has_name(word)),
+        _ => false,
+    };
     match meta {
         MetaItemKind::Word => template.word,
-        MetaItemKind::List(..) => template.list.is_some(),
+        MetaItemKind::List(items) => template.list.is_some() || is_one_allowed_subword(items),
         MetaItemKind::NameValue(lit) if lit.kind.is_str() => template.name_value_str.is_some(),
         MetaItemKind::NameValue(..) => false,
     }
@@ -230,6 +236,7 @@ fn emit_malformed_attribute(
     if let Some(descr) = template.list {
         suggestions.push(format!("#{inner}[{name}({descr})]"));
     }
+    suggestions.extend(template.one_of.iter().map(|&word| format!("#{inner}[{name}({word})]")));
     if let Some(descr) = template.name_value_str {
         suggestions.push(format!("#{inner}[{name} = \"{descr}\"]"));
     }

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
-    fn check_coverage(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
+    /// Checks that `#[coverage(..)]` is applied to a function or closure.
+    fn check_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 {
     pub defn_span: Span,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(passes_coverage_ignored_function_prototype)]
-pub struct IgnoredCoverageFnProto;
-
-#[derive(LintDiagnostic)]
-#[diag(passes_coverage_propagate)]
-pub struct IgnoredCoveragePropagate;
-
-#[derive(LintDiagnostic)]
-#[diag(passes_coverage_fn_defn)]
-pub struct IgnoredCoverageFnDefn;
-
 #[derive(Diagnostic)]
-#[diag(passes_coverage_not_coverable, code = E0788)]
-pub struct IgnoredCoverageNotCoverable {
+#[diag(passes_coverage_not_fn_or_closure, code = E0788)]
+pub struct CoverageNotFnOrClosure {
     #[primary_span]
     pub attr_span: Span,
     #[label]

tests/ui/coverage-attr/bad-syntax.rs

@@ -1,58 +1,45 @@
 #![feature(coverage_attribute)]
+//@ edition: 2021
 
 // Tests the error messages produced (or not produced) by various unusual
 // uses of the `#[coverage(..)]` attribute.
 
-// FIXME(#126658): Multiple coverage attributes with the same value are useless,
-// and should probably produce a diagnostic.
-#[coverage(off)]
+#[coverage(off)] //~ ERROR multiple `coverage` attributes
 #[coverage(off)]
 fn multiple_consistent() {}
 
-// FIXME(#126658): When there are multiple inconsistent coverage attributes,
-// it's unclear which one will prevail.
-#[coverage(off)]
+#[coverage(off)] //~ ERROR multiple `coverage` attributes
 #[coverage(on)]
 fn multiple_inconsistent() {}
 
-#[coverage] //~ ERROR expected `coverage(off)` or `coverage(on)`
+#[coverage] //~ ERROR malformed `coverage` attribute input
 fn bare_word() {}
 
-// FIXME(#126658): This shows as multiple different errors, one of which suggests
-// writing bare `#[coverage]`, which is not allowed.
-#[coverage = true]
-//~^ ERROR expected `coverage(off)` or `coverage(on)`
-//~| ERROR malformed `coverage` attribute input
-//~| HELP the following are the possible correct uses
-//~| SUGGESTION #[coverage(on|off)]
+#[coverage = true] //~ ERROR malformed `coverage` attribute input
 fn key_value() {}
 
-#[coverage()] //~ ERROR expected `coverage(off)` or `coverage(on)`
+#[coverage()] //~ ERROR malformed `coverage` attribute input
 fn list_empty() {}
 
-#[coverage(off, off)] //~ ERROR expected `coverage(off)` or `coverage(on)`
+#[coverage(off, off)] //~ ERROR malformed `coverage` attribute input
 fn list_consistent() {}
 
-#[coverage(off, on)] //~ ERROR expected `coverage(off)` or `coverage(on)`
+#[coverage(off, on)] //~ ERROR malformed `coverage` attribute input
 fn list_inconsistent() {}
 
-#[coverage(bogus)] //~ ERROR expected `coverage(off)` or `coverage(on)`
+#[coverage(bogus)] //~ ERROR malformed `coverage` attribute input
 fn bogus_word() {}
 
-#[coverage(bogus, off)] //~ ERROR expected `coverage(off)` or `coverage(on)`
+#[coverage(bogus, off)] //~ ERROR malformed `coverage` attribute input
 fn bogus_word_before() {}
 
-#[coverage(off, bogus)] //~ ERROR expected `coverage(off)` or `coverage(on)`
+#[coverage(off, bogus)] //~ ERROR malformed `coverage` attribute input
 fn bogus_word_after() {}
 
-#[coverage(off,)]
+#[coverage(off,)] // (OK!)
 fn comma_after() {}
 
-// FIXME(#126658): This shows as multiple different errors.
-#[coverage(,off)]
-//~^ ERROR expected identifier, found `,`
-//~| HELP remove this comma
-//~| ERROR expected `coverage(off)` or `coverage(on)`
+#[coverage(,off)] //~ ERROR expected identifier, found `,`
 fn comma_before() {}
 
 fn main() {}