Add #[coverage(off)] to closures introduced by #[test]/#[bench]

Author: Zalathar

compiler/rustc_builtin_macros/src/lib.rs

@@ -6,6 +6,7 @@
 #![doc(rust_logo)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(array_windows)]
+#![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(decl_macro)]
 #![feature(if_let_guard)]

compiler/rustc_builtin_macros/src/test.rs

@@ -9,6 +9,7 @@ use rustc_errors::{Applicability, DiagnosticBuilder, Level};
 use rustc_expand::base::*;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{ErrorGuaranteed, FileNameDisplayPreference, Span};
+use std::assert_matches::assert_matches;
 use std::iter;
 use thin_vec::{thin_vec, ThinVec};
 
@@ -182,6 +183,16 @@ pub fn expand_test_or_bench(
     // creates $name: $expr
     let field = |name, expr| cx.field_imm(sp, Ident::from_str_and_span(name, sp), expr);
 
+    // Adds `#[coverage(off)]` to a closure, so it won't be instrumented in
+    // `-Cinstrument-coverage` builds.
+    // This requires `#[allow_internal_unstable(coverage_attribute)]` on the
+    // corresponding macro declaration in `core::macros`.
+    let coverage_off = |mut expr: P<ast::Expr>| {
+        assert_matches!(expr.kind, ast::ExprKind::Closure(_));
+        expr.attrs.push(cx.attr_nested_word(sym::coverage, sym::off, sp));
+        expr
+    };
+
     let test_fn = if is_bench {
         // A simple ident for a lambda
         let b = Ident::from_str_and_span("b", attr_sp);
@@ -190,8 +201,9 @@ pub fn expand_test_or_bench(
             sp,
             cx.expr_path(test_path("StaticBenchFn")),
             thin_vec![
+                // #[coverage(off)]
                 // |b| self::test::assert_test_result(
-                cx.lambda1(
+                coverage_off(cx.lambda1(
                     sp,
                     cx.expr_call(
                         sp,
@@ -206,16 +218,17 @@ pub fn expand_test_or_bench(
                         ],
                     ),
                     b,
-                ), // )
+                )), // )
             ],
         )
     } else {
         cx.expr_call(
             sp,
             cx.expr_path(test_path("StaticTestFn")),
             thin_vec![
+                // #[coverage(off)]
                 // || {
-                cx.lambda0(
+                coverage_off(cx.lambda0(
                     sp,
                     // test::assert_test_result(
                     cx.expr_call(
@@ -230,7 +243,7 @@ pub fn expand_test_or_bench(
                             ), // )
                         ],
                     ), // }
-                ), // )
+                )), // )
             ],
         )
     };

library/core/src/macros/mod.rs

@@ -1596,7 +1596,7 @@ pub(crate) mod builtin {
     ///
     /// [the reference]: ../../../reference/attributes/testing.html#the-test-attribute
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[allow_internal_unstable(test, rustc_attrs)]
+    #[allow_internal_unstable(test, rustc_attrs, coverage_attribute)]
     #[rustc_builtin_macro]
     pub macro test($item:item) {
         /* compiler built-in */
@@ -1609,7 +1609,7 @@ pub(crate) mod builtin {
         soft,
         reason = "`bench` is a part of custom test frameworks which are unstable"
     )]
-    #[allow_internal_unstable(test, rustc_attrs)]
+    #[allow_internal_unstable(test, rustc_attrs, coverage_attribute)]
     #[rustc_builtin_macro]
     pub macro bench($item:item) {
         /* compiler built-in */

tests/coverage/bench.cov-map

@@ -6,11 +6,3 @@ Number of expressions: 0
 Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 8, 1) to (start + 0, 39)
 
-Function name: bench::my_bench::{closure#0}
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 07, 01, 00, 09]
-Number of files: 1
-- file 0 => global file 1
-Number of expressions: 0
-Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 7, 1) to (start + 0, 9)
-

tests/coverage/bench.coverage

@@ -4,6 +4,6 @@
    LL|       |
    LL|       |extern crate test;
    LL|       |
-   LL|      1|#[bench]
+   LL|       |#[bench]
    LL|      1|fn my_bench(_b: &mut test::Bencher) {}
 

tests/coverage/test_harness.cov-map

@@ -6,14 +6,6 @@ Number of expressions: 0
 Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 10, 1) to (start + 0, 16)
 
-Function name: test_harness::my_test::{closure#0}
-Raw bytes (9): 0x[01, 01, 00, 01, 01, 09, 01, 00, 08]
-Number of files: 1
-- file 0 => global file 1
-Number of expressions: 0
-Number of file 0 mappings: 1
-- Code(Counter(0)) at (prev + 9, 1) to (start + 0, 8)
-
 Function name: test_harness::unused (unused)
 Raw bytes (9): 0x[01, 01, 00, 01, 00, 07, 01, 00, 0f]
 Number of files: 1

tests/coverage/test_harness.coverage

@@ -6,6 +6,6 @@
    LL|       |#[allow(dead_code)]
    LL|      0|fn unused() {}
    LL|       |
-   LL|      1|#[test]
+   LL|       |#[test]
    LL|      1|fn my_test() {}