Use target.rustflags instead of build.rustflags

CHANGELOG.md

@@ -1,3 +1,11 @@
+# Dev
+## Changes
+
+- Use `target.rustflags` for passing PGO flags instead
+  of `build.rustflags` (https://github.com/Kobzol/cargo-pgo/issues/56).
+  This should make it less likely that PGO flags will be overridden by users' `.cargo/config.toml` files.
+  On the other hand, `cargo pgo` will now override `build.rustflags` set in `config.toml`.
+
 # 0.2.8 (28. 3. 2024)
 ## Fixes
 

src/build.rs

@@ -93,10 +93,13 @@ pub fn cargo_command_with_rustflags(
         (true, _) => {
             // If there's no RUSTFLAGS, and Cargo supports `--config`, use it.
             // The user might have some flags in their config.toml file(s), and
-            // `--config build.rustflags` will append to it instead of overwriting it.
+            // `--config target.*.rustflags` will append to it instead of overwriting it.
+            // We use target RUSTFLAGS instead of e.g. build rustflags, because it has a higher
+            // precedence. See https://github.com/Kobzol/cargo-pgo/issues/56 for more details.
             final_cargo_args.push("--config".to_string());
 
-            let mut flags = String::from("build.rustflags=[");
+            // `cfg(all())` should match any target.
+            let mut flags = String::from("target.'cfg(all())'.rustflags=[");
             for (index, flag) in rustflags.into_iter().enumerate() {
                 if index > 0 {
                     flags.push(',');

tests/integration/pgo.rs

@@ -282,7 +282,7 @@ fn test_respect_existing_rustflags() -> anyhow::Result<()> {
 
 /// This only works for Rust 1.63+.
 #[test]
-fn test_respect_existing_rustflags_from_config() -> anyhow::Result<()> {
+fn test_override_build_rustflags_from_config() -> anyhow::Result<()> {
     if !version_check::is_min_version("1.63.0").unwrap_or(false) {
         return Ok(());
     }
@@ -296,6 +296,34 @@ rustflags = ["-Ctarget-cpu=native"]
 "#,
     );
 
+    let output = project.cmd(&["build", "--", "-v"]).run()?;
+    println!("{}", output.stderr());
+    assert!(!output.stderr().contains("-Ctarget-cpu=native"));
+    assert!(output.stderr().contains("-Cprofile-generate"));
+    output.assert_ok();
+
+    Ok(())
+}
+
+#[test]
+fn test_respect_existing_target_rustflags_from_config() -> anyhow::Result<()> {
+    if !version_check::is_min_version("1.63.0").unwrap_or(false) {
+        return Ok(());
+    }
+
+    let target = get_default_target()?;
+
+    let mut project = init_cargo_project()?;
+    project.file(
+        ".cargo/config.toml",
+        &format!(
+            r#"
+[target.{target}]
+rustflags = ["-Ctarget-cpu=native"]
+"#
+        ),
+    );
+
     let output = project.cmd(&["build", "--", "-v"]).run()?;
     println!("{}", output.stderr());
     assert!(output.stderr().contains("-Ctarget-cpu=native"));