1 files changed, 32 insertions, 0 deletions
diff --git a/src/libsyntax/codemap.rs b/src/libsyntax/codemap.rs
index 042a1bd0781..5eac6546c6b 100644
--- a/src/libsyntax/codemap.rs
+++ b/src/libsyntax/codemap.rs
@@ -568,6 +568,38 @@ impl CodeMap {
             ExpnId(i) => f(Some(&(*self.expansions.borrow())[i as uint]))
         }
     }
+
+    /// Check if a span is "internal" to a macro. This means that it is entirely generated by a
+    /// macro expansion and contains no code that was passed in as an argument.
+    pub fn span_is_internal(&self, span: Span) -> bool {
+        // first, check if the given expression was generated by a macro or not
+        // we need to go back the expn_info tree to check only the arguments
+        // of the initial macro call, not the nested ones.
+        let mut is_internal = false;
+        let mut expnid = span.expn_id;
+        while self.with_expn_info(expnid, |expninfo| {
+            match expninfo {
+                Some(ref info) => {
+                    // save the parent expn_id for next loop iteration
+                    expnid = info.call_site.expn_id;
+                    if info.callee.span.is_none() {
+                        // it's a compiler built-in, we *really* don't want to mess with it
+                        // so we skip it, unless it was called by a regular macro, in which case
+                        // we will handle the caller macro next turn
+                        is_internal = true;
+                        true // continue looping
+                    } else {
+                        // was this expression from the current macro arguments ?
+                        is_internal = !( span.lo > info.call_site.lo &&
+                                         span.hi < info.call_site.hi );
+                        true // continue looping
+                    }
+                },
+                _ => false // stop looping
+            }
+        }) { /* empty while loop body */ }
+        return is_internal;
+    }
 }
 
 #[cfg(test)]