add support for proc macros

Author: beepster4096

compiler/rustc_expand/src/proc_macro_server.rs

@@ -375,6 +375,10 @@ impl server::Types for Rustc<'_, '_> {
 }
 
 impl server::FreeFunctions for Rustc<'_, '_> {
+    fn injected_env_var(&mut self, var: &str) -> Option<String> {
+        self.ecx.sess.opts.injected_env_vars.get(var).cloned()
+    }
+
     fn track_env_var(&mut self, var: &str, value: Option<&str>) {
         self.sess()
             .env_depinfo

library/proc_macro/src/bridge/mod.rs

@@ -54,6 +54,7 @@ macro_rules! with_api {
         $m! {
             FreeFunctions {
                 fn drop($self: $S::FreeFunctions);
+                fn injected_env_var(var: &str) -> Option<String>;
                 fn track_env_var(var: &str, value: Option<&str>);
                 fn track_path(path: &str);
                 fn literal_from_str(s: &str) -> Result<Literal<$S::Span, $S::Symbol>, ()>;

library/proc_macro/src/lib.rs

@@ -1505,7 +1505,10 @@ pub mod tracked_env {
     #[unstable(feature = "proc_macro_tracked_env", issue = "99515")]
     pub fn var<K: AsRef<OsStr> + AsRef<str>>(key: K) -> Result<String, VarError> {
         let key: &str = key.as_ref();
-        let value = env::var(key);
+        let injected_value = crate::bridge::client::FreeFunctions::injected_env_var(key);
+        let env_value = env::var(key);
+
+        let value = injected_value.map_or_else(env_value, Ok);
         crate::bridge::client::FreeFunctions::track_env_var(key, value.as_deref().ok());
         value
     }