fix: enable linux shared-library-safe v8 tls mode by default

Author: mplemay

README.md

@@ -157,6 +157,18 @@ is recommended.
 Arguments can be passed to `gn` by setting the `$GN_ARGS` environmental
 variable.
 
+For Linux targets, `rusty_v8` now defaults to defining
+`V8_TLS_USED_IN_LIBRARY` via GN args when building from source so the produced
+static archive can be linked into downstream `cdylib`/shared-library targets.
+The default injected argument is:
+
+```bash
+GN_ARGS='extra_cflags=["-DV8_TLS_USED_IN_LIBRARY"]'
+```
+
+Linux prebuilt release archives published by this repository are built with
+this shared-library-compatible TLS mode.
+
 Env vars used in when building from source: `SCCACHE`, `CCACHE`, `GN`, `NINJA`,
 `CLANG_BASE_PATH`, `GN_ARGS`
 

build.rs

@@ -346,11 +346,20 @@ fn build_v8(is_asan: bool) {
     println!("cargo:warning=Not using sccache or ccache");
   }
 
+  // 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());
+  }
   // cross-compilation setup
   if target_arch == "aarch64" {
     gn_args.push(r#"target_cpu="arm64""#.to_string());