Merge #3671

3671: Add identity expansion checking in ill-form expansion  r=flodiebold a=edwin0cheng

This PR try to add more checking code in error case in macro expansion. The bug in #3642 is introduced by  #3580 , which allow ill-form macro expansion in *all* kind of macro expansions. 

In general we should separate hypothetical macro expansion and the actual macro expansion call. However, currently the `Semantic`  workflow we are using only support single macro expansion type, we might want to review it and make it works in both ways. (Maybe add a field in `MacroCallLoc` for differentiation) 

Fix #3642

Co-authored-by: Edwin Cheng <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/algo.rs b/crates/ra_syntax/src/algo.rs
index 344cf0fbe..ffdbdc767 100644
--- a/crates/ra_syntax/src/algo.rs
+++ b/crates/ra_syntax/src/algo.rs
@@ -95,6 +95,10 @@ impl TreeDiff {
             builder.replace(from.text_range(), to.to_string())
         }
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.replacements.is_empty()
+    }
 }
 
 /// Finds minimal the diff, which, applied to `from`, will result in `to`.