Default to linking against release v8 builds (#783)

Unless $V8_FORCE_DEBUG=true to speedup CI for main deno repo

README.md

@@ -42,6 +42,13 @@ from github to get the static lib. To disable this build using the
 When making changes to rusty_v8 itself, it should be tested by build from
 source. The CI always builds from source.
 
+## The `V8_FORCE_DEBUG` environment variable
+
+By default `rusty_v8` will link against release builds of `v8`, if you want to
+use a debug build of `v8` set `V8_FORCE_DEBUG=true`.
+
+We default to release builds of `v8` due to performance & CI reasons in `deno`.
+
 ## The `RUSTY_V8_MIRROR` environment variable
 
 Tells the build script where to get binary builds from. Understands

build.rs

@@ -206,14 +206,24 @@ fn static_lib_url() -> String {
     env::var("RUSTY_V8_MIRROR").unwrap_or_else(|_| default_base.into());
   let version = env::var("CARGO_PKG_VERSION").unwrap();
   let target = env::var("TARGET").unwrap();
+
+  // Note: we always use the release build on windows.
   if cfg!(target_os = "windows") {
-    // Note: we always use the release build on windows.
+    return format!("{}/v{}/rusty_v8_release_{}.lib", base, version, target);
-    format!("{}/v{}/rusty_v8_release_{}.lib", base, version, target)
-  } else {
-    let profile = env::var("PROFILE").unwrap();
-    assert!(profile == "release" || profile == "debug");
-    format!("{}/v{}/librusty_v8_{}_{}.a", base, version, profile, target)
   }
+  // Use v8 in release mode unless $V8_FORCE_DEBUG=true
+  let profile = match env_bool("V8_FORCE_DEBUG") {
+    true => "debug",
+    _ => "release",
+  };
+  format!("{}/v{}/librusty_v8_{}_{}.a", base, version, profile, target)
+}
+
+fn env_bool(key: &str) -> bool {
+  matches!(
+    env::var(key).unwrap_or_default().as_str(),
+    "true" | "1" | "yes"
+  )
 }
 
 fn static_lib_name() -> &'static str {