rust-project: Warn on unowned files

Summary: Log a warning message if we can't determine the owner of a file passed to `develop`, but _is_ in fbsource (i.e., we already log if buck can't determine an owner because it's outside of the repo, but now we also log if it's in the repo but unowned).

Reviewed By: Wilfred

Differential Revision: D57947948

fbshipit-source-id: 1fd06b41341503b58e39748e994cd14f18880a6c

integrations/rust-project/src/cli/develop.rs

@@ -169,7 +169,7 @@ impl Develop {
     }
 
     pub fn resolve_file_owners(&self, files: &[PathBuf]) -> FxHashMap<PathBuf, Vec<Target>> {
-        match self.buck.query_owner(&files) {
+        let owners = match self.buck.query_owner(&files) {
             Ok(owners) => owners,
             Err(_) => {
                 let mut owners = FxHashMap::default();
@@ -187,7 +187,15 @@ impl Develop {
 
                 owners
             }
+        };
+
+        for (file, targets) in owners.iter() {
+            if targets.is_empty() {
+                warn!(file = ?file, "Buck returned zero targets for this file.");
+            }
         }
+
+        owners
     }
 
     pub(crate) fn run(&self, targets: Vec<Target>) -> Result<JsonProject, anyhow::Error> {