adds feature gating of no_coverage at either crate- or function-level

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -16,10 +16,19 @@ pub fn expand_deriving_eq(
     push: &mut dyn FnMut(Annotatable),
 ) {
     let inline = cx.meta_word(span, sym::inline);
+    let no_coverage_ident =
+        rustc_ast::attr::mk_nested_word_item(Ident::new(sym::no_coverage, span));
+    let no_coverage_feature =
+        rustc_ast::attr::mk_list_item(Ident::new(sym::feature, span), vec![no_coverage_ident]);
     let no_coverage = cx.meta_word(span, sym::no_coverage);
     let hidden = rustc_ast::attr::mk_nested_word_item(Ident::new(sym::hidden, span));
     let doc = rustc_ast::attr::mk_list_item(Ident::new(sym::doc, span), vec![hidden]);
-    let attrs = vec![cx.attribute(inline), cx.attribute(no_coverage), cx.attribute(doc)];
+    let attrs = vec![
+        cx.attribute(inline),
+        cx.attribute(no_coverage_feature),
+        cx.attribute(no_coverage),
+        cx.attribute(doc),
+    ];
     let trait_def = TraitDef {
         span,
         attributes: Vec::new(),

compiler/rustc_feature/src/active.rs

@@ -649,6 +649,10 @@ declare_features! (
     /// Allows `extern "wasm" fn`
     (active, wasm_abi, "1.53.0", Some(83788), None),
 
+    /// Allows function attribute `#[no_coverage]`, to bypass coverage
+    /// instrumentation of that function.
+    (active, no_coverage, "1.53.0", Some(84605), None),
+
     /// Allows trait bounds in `const fn`.
     (active, const_fn_trait_bound, "1.53.0", Some(57563), None),
 

compiler/rustc_feature/src/builtin_attrs.rs

@@ -264,7 +264,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     // Code generation:
     ungated!(inline, AssumedUsed, template!(Word, List: "always|never")),
-    ungated!(no_coverage, AssumedUsed, template!(Word)),
     ungated!(cold, AssumedUsed, template!(Word)),
     ungated!(no_builtins, AssumedUsed, template!(Word)),
     ungated!(target_feature, AssumedUsed, template!(List: r#"enable = "name""#)),
@@ -274,6 +273,13 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         template!(List: "address, memory, thread"),
         experimental!(no_sanitize)
     ),
+    ungated!(
+        // Not exclusively gated at the crate level (though crate-level is
+        // supported). The feature can alternatively be enabled on individual
+        // functions.
+        no_coverage, AssumedUsed,
+        template!(Word),
+    ),
 
     // FIXME: #14408 assume docs are used since rustdoc looks at them.
     ungated!(doc, AssumedUsed, template!(List: "hidden|inline|...", NameValueStr: "string")),

compiler/rustc_typeck/src/collect.rs

@@ -2661,6 +2661,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
     let mut inline_span = None;
     let mut link_ordinal_span = None;
     let mut no_sanitize_span = None;
+    let mut no_coverage_feature_enabled = false;
+    let mut no_coverage_attr = None;
     for attr in attrs.iter() {
         if tcx.sess.check_name(attr, sym::cold) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
@@ -2724,8 +2726,15 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
         } else if tcx.sess.check_name(attr, sym::no_mangle) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
+        } else if attr.has_name(sym::feature) {
+            if let Some(list) = attr.meta_item_list() {
+                if list.iter().any(|nested_meta_item| nested_meta_item.has_name(sym::no_coverage)) {
+                    tcx.sess.mark_attr_used(attr);
+                    no_coverage_feature_enabled = true;
+                }
+            }
         } else if tcx.sess.check_name(attr, sym::no_coverage) {
-            codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_COVERAGE;
+            no_coverage_attr = Some(attr);
         } else if tcx.sess.check_name(attr, sym::rustc_std_internal_symbol) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
         } else if tcx.sess.check_name(attr, sym::used) {
@@ -2936,6 +2945,23 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
         }
     }
 
+    if let Some(no_coverage_attr) = no_coverage_attr {
+        if tcx.sess.features_untracked().no_coverage || no_coverage_feature_enabled {
+            codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_COVERAGE
+        } else {
+            let mut err = feature_err(
+                &tcx.sess.parse_sess,
+                sym::no_coverage,
+                no_coverage_attr.span,
+                "the `#[no_coverage]` attribute is an experimental feature",
+            );
+            if tcx.sess.parse_sess.unstable_features.is_nightly_build() {
+                err.help("or, alternatively, add `#[feature(no_coverage)]` to the function");
+            }
+            err.emit();
+        }
+    }
+
     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
         if !attr.has_name(sym::inline) {
             return ia;

library/core/src/cmp.rs

@@ -274,6 +274,7 @@ pub trait Eq: PartialEq<Self> {
     //
     // This should never be implemented by hand.
     #[doc(hidden)]
+    #[cfg_attr(not(bootstrap), feature(no_coverage))]
     #[cfg_attr(not(bootstrap), no_coverage)]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]

src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.no_cov_crate.txt

@@ -0,0 +1,18 @@
+    1|       |// Enables `no_coverage` on the entire crate
+    2|       |#![feature(no_coverage)]
+    3|       |
+    4|       |#[no_coverage]
+    5|       |fn do_not_add_coverage_1() {
+    6|       |    println!("called but not covered");
+    7|       |}
+    8|       |
+    9|       |#[no_coverage]
+   10|       |fn do_not_add_coverage_2() {
+   11|       |    println!("called but not covered");
+   12|       |}
+   13|       |
+   14|      1|fn main() {
+   15|      1|    do_not_add_coverage_1();
+   16|      1|    do_not_add_coverage_2();
+   17|      1|}
+

src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.no_cov_func.txt

@@ -0,0 +1,19 @@
+    1|       |// Enables `no_coverage` on individual functions
+    2|       |
+    3|       |#[feature(no_coverage)]
+    4|       |#[no_coverage]
+    5|       |fn do_not_add_coverage_1() {
+    6|       |    println!("called but not covered");
+    7|       |}
+    8|       |
+    9|       |#[no_coverage]
+   10|       |#[feature(no_coverage)]
+   11|       |fn do_not_add_coverage_2() {
+   12|       |    println!("called but not covered");
+   13|       |}
+   14|       |
+   15|      1|fn main() {
+   16|      1|    do_not_add_coverage_1();
+   17|      1|    do_not_add_coverage_2();
+   18|      1|}
+

src/test/run-make-fulldeps/coverage/no_cov_crate.rs

@@ -0,0 +1,17 @@
+// Enables `no_coverage` on the entire crate
+#![feature(no_coverage)]
+
+#[no_coverage]
+fn do_not_add_coverage_1() {
+    println!("called but not covered");
+}
+
+#[no_coverage]
+fn do_not_add_coverage_2() {
+    println!("called but not covered");
+}
+
+fn main() {
+    do_not_add_coverage_1();
+    do_not_add_coverage_2();
+}

src/test/run-make-fulldeps/coverage/no_cov_func.rs

@@ -0,0 +1,18 @@
+// Enables `no_coverage` on individual functions
+
+#[feature(no_coverage)]
+#[no_coverage]
+fn do_not_add_coverage_1() {
+    println!("called but not covered");
+}
+
+#[no_coverage]
+#[feature(no_coverage)]
+fn do_not_add_coverage_2() {
+    println!("called but not covered");
+}
+
+fn main() {
+    do_not_add_coverage_1();
+    do_not_add_coverage_2();
+}

src/test/ui/feature-gates/feature-gate-no_coverage.rs

@@ -0,0 +1,8 @@
+#![crate_type = "lib"]
+
+#[no_coverage]
+#[feature(no_coverage)] // does not have to be enabled before `#[no_coverage]`
+fn no_coverage_is_enabled_on_this_function() {}
+
+#[no_coverage] //~ ERROR the `#[no_coverage]` attribute is an experimental feature
+fn requires_feature_no_coverage() {}

src/test/ui/feature-gates/feature-gate-no_coverage.stderr

@@ -0,0 +1,13 @@
+error[E0658]: the `#[no_coverage]` attribute is an experimental feature
+  --> $DIR/feature-gate-no_coverage.rs:7:1
+   |
+LL | #[no_coverage]
+   | ^^^^^^^^^^^^^^
+   |
+   = note: see issue #84605 <https://github.com/rust-lang/rust/issues/84605> for more information
+   = help: add `#![feature(no_coverage)]` to the crate attributes to enable
+   = help: or, alternatively, add `#[feature(no_coverage)]` to the function
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.