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 <edwin0cheng@gmail.com>

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 propagate 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_hir_ty/src/tests/regression.rs

@@ -453,3 +453,34 @@ pub mod str {
     // should be Option<char>, but currently not because of Chalk ambiguity problem
     assert_eq!("(Option<{unknown}>, Option<{unknown}>)", super::type_at_pos(&db, pos));
 }
+
+#[test]
+fn issue_3642_bad_macro_stackover() {
+    let (db, pos) = TestDB::with_position(
+        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
+        }
+    };
+}"#,
+    );
+
+    assert_eq!("()", super::type_at_pos(&db, pos));
+}

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`.