feat(cargo-codspeed): add test for target.rustflags in config

Author: not-matthias

crates/cargo-codspeed/tests/cargo_config.in/.cargo/config.toml

@@ -1,2 +1 @@
-[build]
-rustflags = ["--cfg", "custom_feature_flag"]
+# This will be generated by the test

crates/cargo-codspeed/tests/cargo_config.rs

@@ -1,12 +1,29 @@
-use std::process::Command;
+use std::{path::PathBuf, process::Command};
 
 mod helpers;
 use helpers::*;
 
-#[test]
-fn test_cargo_config_rustflags() {
+const BUILD_RUSTFLAGS: &str = r#"
+[build]
+rustflags = ["--cfg", "custom_feature_flag"]
+"#;
+
+const TARGET_RUSTFLAGS: &str = r#"
+[build]
+rustflags = ["--cfg", "this_will_be_overridden"]
+
+[target.'cfg(all())']
+rustflags = ["--cfg custom_feature_flag"]
+"#;
+
+fn build_and_run_cargo_bench_with_config(cargo_config: &str) {
+    // Create a temporary directory and write the .cargo/config
     let tmp_dir = setup("tests/cargo_config.in", Project::Simple);
 
+    let config_path = PathBuf::from(&tmp_dir).join(".cargo").join("config.toml");
+    std::fs::create_dir_all(config_path.parent().unwrap()).unwrap();
+    std::fs::write(config_path, cargo_config).unwrap();
+
     // Test that cargo bench works with the custom flag
     let output = Command::new("cargo")
         .arg("bench")
@@ -33,3 +50,13 @@ fn test_cargo_config_rustflags() {
 
     teardown(tmp_dir);
 }
+
+#[test]
+fn test_cargo_config_build_rustflags() {
+    build_and_run_cargo_bench_with_config(BUILD_RUSTFLAGS);
+}
+
+#[test]
+fn test_cargo_config_target_rustflags() {
+    build_and_run_cargo_bench_with_config(TARGET_RUSTFLAGS);
+}