Add identity expansion checking

crates/ra_hir_expand/src/db.rs

@@ -6,7 +6,7 @@ use mbe::{ExpandResult, MacroRules};
 use ra_db::{salsa, SourceDatabase};
 use ra_parser::FragmentKind;
 use ra_prof::profile;
-use ra_syntax::{AstNode, Parse, SyntaxKind::*, SyntaxNode};
+use ra_syntax::{algo::diff, AstNode, Parse, SyntaxKind::*, SyntaxNode};
 
 use crate::{
     ast_id_map::AstIdMap, BuiltinDeriveExpander, BuiltinFnLikeExpander, EagerCallLoc, EagerMacroId,
@@ -238,7 +238,7 @@ pub fn parse_macro_with_arg(
     } else {
         db.macro_expand(macro_call_id)
     };
-    if let Some(err) = err {
+    if let Some(err) = &err {
         // Note:
         // The final goal we would like to make all parse_macro success,
         // such that the following log will not call anyway.
@@ -272,7 +272,25 @@ pub fn parse_macro_with_arg(
     let fragment_kind = to_fragment_kind(db, macro_call_id);
 
     let (parse, rev_token_map) = mbe::token_tree_to_syntax_node(&tt, fragment_kind).ok()?;
-    Some((parse, Arc::new(rev_token_map)))
+
+    if err.is_none() {
+        Some((parse, Arc::new(rev_token_map)))
+    } else {
+        // FIXME:
+        // In future, we should proprate the actual error with recovery information
+        // instead of ignore the error here.
+
+        // Safe check for recurisve identity macro
+        let node = parse.syntax_node();
+        let file: HirFileId = macro_file.into();
+        let call_node = file.call_node(db)?;
+
+        if !diff(&node, &call_node.value).is_empty() {
+            Some((parse, Arc::new(rev_token_map)))
+        } else {
+            None
+        }
+    }
 }
 
 /// Given a `MacroCallId`, return what `FragmentKind` it belongs to.

crates/ra_ide/src/diagnostics.rs

@@ -715,4 +715,34 @@ fn main() {
             check_struct_shorthand_initialization,
         );
     }
+
+    #[test]
+    fn test_bad_macro_stackover() {
+        check_no_diagnostic(
+            r#"
+                //- /main.rs
+    #[macro_export]
+    macro_rules! match_ast {
+        (match $node:ident { $($tt:tt)* }) => { match_ast!(match ($node) { $($tt)* }) };
+
+        (match ($node:expr) {
+            $( ast::$ast:ident($it:ident) => $res:expr, )*
+            _ => $catch_all:expr $(,)?
+        }) => {{
+            $( if let Some($it) = ast::$ast::cast($node.clone()) { $res } else )*
+            { $catch_all }
+        }};
+    }
+
+    fn main() {
+        let anchor = match_ast! {
+            match parent {
+                as => {},
+                _ => return None
+            }
+        };
+    }
+            "#,
+        );
+    }
 }

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`.