Set current working directory for procedural macros

crates/proc_macro_api/src/lib.rs

@@ -156,12 +156,18 @@ pub fn expand(
         attr: Option<&Subtree>,
         env: Vec<(String, String)>,
     ) -> Result<Result<Subtree, PanicMessage>, ServerError> {
+        let current_dir = env
+            .iter()
+            .find(|(name, _)| name == "CARGO_MANIFEST_DIR")
+            .map(|(_, value)| value.clone());
+
         let task = ExpandMacro {
             macro_body: FlatTree::new(subtree),
             macro_name: self.name.to_string(),
             attributes: attr.map(FlatTree::new),
             lib: self.dylib_path.to_path_buf().into(),
             env,
+            current_dir,
         };
 
         let request = msg::Request::ExpandMacro(task);

crates/proc_macro_api/src/msg.rs

@@ -48,6 +48,8 @@ pub struct ExpandMacro {
 
     /// Environment variables to set during macro expansion.
     pub env: Vec<(String, String)>,
+
+    pub current_dir: Option<String>,
 }
 
 pub trait Message: Serialize + DeserializeOwned {
@@ -143,6 +145,7 @@ fn test_proc_macro_rpc_works() {
             attributes: None,
             lib: std::env::current_dir().unwrap(),
             env: Default::default(),
+            current_dir: Default::default(),
         };
 
         let json = serde_json::to_string(&task).unwrap();

crates/proc_macro_srv/src/lib.rs

@@ -43,6 +43,16 @@ pub fn expand(&mut self, task: ExpandMacro) -> Result<FlatTree, PanicMessage> {
             prev_env.insert(k.as_str(), env::var_os(k));
             env::set_var(k, v);
         }
+        let prev_working_dir = match task.current_dir {
+            Some(dir) => {
+                let prev_working_dir = std::env::current_dir().ok();
+                if let Err(err) = std::env::set_current_dir(&dir) {
+                    eprintln!("Failed to set the current working dir to {}. Error: {:?}", dir, err)
+                }
+                prev_working_dir
+            }
+            None => None,
+        };
 
         let macro_body = task.macro_body.to_subtree();
         let attributes = task.attributes.map(|it| it.to_subtree());
@@ -56,6 +66,15 @@ pub fn expand(&mut self, task: ExpandMacro) -> Result<FlatTree, PanicMessage> {
                 None => env::remove_var(k),
             }
         }
+        if let Some(dir) = prev_working_dir {
+            if let Err(err) = std::env::set_current_dir(&dir) {
+                eprintln!(
+                    "Failed to set the current working dir to {}. Error: {:?}",
+                    dir.display(),
+                    err
+                )
+            }
+        }
 
         result.map_err(PanicMessage)
     }