fix: preserve raw gn args for linux tls override

Author: mplemay

build.rs

@@ -348,18 +348,12 @@ fn build_v8(is_asan: bool) {
 
   // Use the shared-library-safe TLS mode by default on Linux so downstream
   // cdylibs can link rusty_v8 archives.
-  let mut has_tls_library_mode_define = false;
-  if let Ok(args) = env::var("GN_ARGS") {
-    for arg in args.split_whitespace() {
-      if arg.contains("V8_TLS_USED_IN_LIBRARY") {
-        has_tls_library_mode_define = true;
-      }
-      gn_args.push(arg.to_string());
-    }
-  }
-  if target_os == "linux" && !has_tls_library_mode_define {
-    gn_args.push(r#"extra_cflags=["-DV8_TLS_USED_IN_LIBRARY"]"#.to_string());
-  }
+  let raw_gn_args = env::var("GN_ARGS").ok();
+  add_user_gn_args_and_linux_tls_default(
+    &mut gn_args,
+    target_os,
+    raw_gn_args.as_deref(),
+  );
   // cross-compilation setup
   if target_arch == "aarch64" {
     gn_args.push(r#"target_cpu="arm64""#.to_string());
@@ -443,6 +437,24 @@ fn build_v8(is_asan: bool) {
   build("rusty_v8", None);
 }
 
+fn add_user_gn_args_and_linux_tls_default(
+  gn_args: &mut Vec<String>,
+  target_os: &str,
+  raw_gn_args: Option<&str>,
+) {
+  let raw_gn_args = raw_gn_args.filter(|args| !args.trim().is_empty());
+  let has_tls_library_mode_define =
+    raw_gn_args.is_some_and(|args| args.contains("V8_TLS_USED_IN_LIBRARY"));
+
+  if let Some(args) = raw_gn_args {
+    gn_args.push(args.to_string());
+  }
+
+  if target_os == "linux" && !has_tls_library_mode_define {
+    gn_args.push(r#"extra_cflags=["-DV8_TLS_USED_IN_LIBRARY"]"#.to_string());
+  }
+}
+
 fn print_gn_args(gn_out_dir: &Path) {
   assert!(
     Command::new(gn())
@@ -1240,4 +1252,60 @@ edge [fontsize=10]
     assert!(files.contains("../../../example/src/count_bytes.py"));
     assert!(!files.contains("obj/hello/hello.o"));
   }
+
+  #[test]
+  fn test_linux_tls_override_detected_in_spaced_array() {
+    let mut gn_args = Vec::new();
+
+    add_user_gn_args_and_linux_tls_default(
+      &mut gn_args,
+      "linux",
+      Some(r#"extra_cflags=[ "-O2", "-DV8_TLS_USED_IN_LIBRARY" ]"#),
+    );
+
+    assert_eq!(
+      gn_args,
+      vec![r#"extra_cflags=[ "-O2", "-DV8_TLS_USED_IN_LIBRARY" ]"#.to_string()]
+    );
+  }
+
+  #[test]
+  fn test_quoted_whitespace_gn_args_preserved_and_tls_default_injected() {
+    let mut gn_args = Vec::new();
+
+    add_user_gn_args_and_linux_tls_default(
+      &mut gn_args,
+      "linux",
+      Some(r#"clang_base_path="/tmp/clang with spaces""#),
+    );
+
+    assert_eq!(
+      gn_args,
+      vec![
+        r#"clang_base_path="/tmp/clang with spaces""#.to_string(),
+        r#"extra_cflags=["-DV8_TLS_USED_IN_LIBRARY"]"#.to_string(),
+      ]
+    );
+  }
+
+  #[test]
+  fn test_whitespace_only_gn_args_skipped() {
+    let mut gn_args = Vec::new();
+
+    add_user_gn_args_and_linux_tls_default(&mut gn_args, "macos", Some("   "));
+
+    assert!(gn_args.is_empty());
+  }
+
+  #[test]
+  fn test_linux_tls_default_injected_without_override() {
+    let mut gn_args = Vec::new();
+
+    add_user_gn_args_and_linux_tls_default(&mut gn_args, "linux", None);
+
+    assert_eq!(
+      gn_args,
+      vec![r#"extra_cflags=["-DV8_TLS_USED_IN_LIBRARY"]"#.to_string()]
+    );
+  }
 }