Set cfg(coverage) to easily use #[no_coverage]

CHANGELOG.md

@@ -10,6 +10,8 @@ Note: In this file, do not use the hard wrap in the middle of a sentence for com
 
 ## [Unreleased]
 
+- [Set `cfg(coverage)` to easily use `#[no_coverage]`.](https://github.com/taiki-e/cargo-llvm-cov/pull/72)
+
 - [Add `--quiet`, `--doc`, and `--jobs` options.](https://github.com/taiki-e/cargo-llvm-cov/pull/70)
 
 ## [0.1.1] - 2021-08-25

README.md

@@ -18,6 +18,7 @@ This is a wrapper around rustc [`-Z instrument-coverage`][instrument-coverage] a
 
 - [Usage](#usage)
   - [Continuous Integration](#continuous-integration)
+  - [Exclude function from coverage](#exclude-function-from-coverage)
 - [Installation](#installation)
 - [Known limitations](#known-limitations)
 - [License](#license)
@@ -269,6 +270,7 @@ cargo llvm-cov --no-report --features b
 cargo llvm-cov --no-run --lcov
 ```
 
+
 ### Continuous Integration
 
 Here is an example of GitHub Actions workflow that uploads coverage to [Codecov].
@@ -299,6 +301,21 @@ jobs:
 
 **NOTE:** Currently, only line coverage is available on Codecov. This is because `-Z instrument-coverage` does not support branch coverage and Codecov does not support region coverage. See also [#8], [#12], and [#20].
 
+### Exclude function from coverage
+
+To exclude the specific function from coverage, use the [`#[no_coverage]` attribute][rust-lang/rust#84605].
+
+Since `#[no_coverage]` is unstable, it is recommended to use it together with `cfg(coverage)` set by cargo-llvm-cov.
+
+```rust
+#![cfg_attr(coverage, feature(no_coverage))]
+
+#[cfg_attr(coverage, no_coverage)]
+fn exclude_from_coverage() {
+    // ...
+}
+```
+
 ## Installation
 
 <!-- omit in toc -->
@@ -357,6 +374,7 @@ See also [the code-coverage-related issues reported in rust-lang/rust](https://g
 [instrument-coverage]: https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/instrument-coverage.html
 [rust-lang/rust#79417]: https://github.com/rust-lang/rust/issues/79417
 [rust-lang/rust#79649]: https://github.com/rust-lang/rust/issues/79649
+[rust-lang/rust#84605]: https://github.com/rust-lang/rust/issues/84605
 [rust-lang/rust#86177]: https://github.com/rust-lang/rust/issues/86177
 
 ## License

src/main.rs

@@ -115,11 +115,9 @@ fn run_test(cx: &Context) -> Result<()> {
     let llvm_profile_file = cx.target_dir.join(format!("{}-%m.profraw", cx.package_name));
 
     let rustflags = &mut cx.env.rustflags.clone().unwrap_or_default();
+    rustflags.push(" -Z instrument-coverage --cfg coverage");
     // --remap-path-prefix is needed because sometimes macros are displayed with absolute path
-    rustflags.push(format!(
-        " -Z instrument-coverage --remap-path-prefix {}/=",
-        cx.metadata.workspace_root
-    ));
+    rustflags.push(format!(" --remap-path-prefix {}/=", cx.metadata.workspace_root));
     if cx.target.is_none() {
         rustflags.push(" --cfg trybuild_no_target");
     }

tests/auxiliary/json.rs

@@ -146,7 +146,7 @@ mod tests {
         .unwrap()
         .filter_map(Result::ok)
         .collect();
-        assert_eq!(files.len(), 38);
+        assert_eq!(files.len(), 40);
 
         for file in files {
             let s = fs::read_to_string(file).unwrap();