Undo previous changes, keeping the release note and tests

Author: Sirraide

clang/docs/ReleaseNotes.rst

@@ -457,6 +457,8 @@ Bug Fixes to C++ Support
   containing outer unexpanded parameters were not correctly expanded. (#GH101754)
 - Fixed a bug in constraint expression comparison where the ``sizeof...`` expression was not handled properly
   in certain friend declarations. (#GH93099)
+- Clang no longer crashes when a lambda contains an invalid block declaration that contains an unexpanded
+  parameter pack. (#GH109148)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaExpr.cpp

@@ -16379,6 +16379,8 @@ ExprResult Sema::ActOnBlockStmtExpr(SourceLocation CaretLoc,
   if (getCurFunction())
     getCurFunction()->addBlock(BD);
 
+  // This can happen if the block's return type is deduced, but
+  // the return expression is invalid.
   if (BD->isInvalidDecl())
     return CreateRecoveryExpr(Result->getBeginLoc(), Result->getEndLoc(),
                               {Result}, Result->getType());

clang/test/SemaCXX/block-unexpanded-pack.cpp

@@ -0,0 +1,48 @@
+// RUN: %clang_cc1 -fblocks -triple x86_64-apple-darwin -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fblocks -triple x86_64-apple-darwin -fsyntax-only -verify %s -frecovery-ast -frecovery-ast-type
+
+// This checks that when a block is discarded, the enclosing lambda’s
+// unexpanded parameter pack flag is reset to what it was before the
+// block is parsed so we don't crash when trying to diagnose unexpanded
+// parameter packs in the lambda.
+
+template <typename ...Ts>
+void gh109148() {
+  (^Ts); // expected-error {{expected expression}} expected-error {{unexpanded parameter pack 'Ts'}}
+
+  [] {
+    (^Ts); // expected-error {{expected expression}}
+    ^Ts;   // expected-error {{expected expression}}
+    ^(Ts); // expected-error {{expected expression}}
+    ^ Ts); // expected-error {{expected expression}}
+  };
+
+  ([] {
+    (^Ts); // expected-error {{expected expression}}
+    ^Ts;   // expected-error {{expected expression}}
+    ^(Ts); // expected-error {{expected expression}}
+    ^ Ts); // expected-error {{expected expression}}
+  }, ...); // expected-error {{pack expansion does not contain any unexpanded parameter packs}}
+
+  [] { // expected-error {{unexpanded parameter pack 'Ts'}}
+    ^ (Ts) {};
+  };
+
+  [] { // expected-error {{unexpanded parameter pack 'Ts'}}
+    (void) ^ { Ts x; };
+  };
+
+  [] { // expected-error {{unexpanded parameter pack 'Ts'}}
+    Ts s;
+    (^Ts); // expected-error {{expected expression}}
+  };
+
+  ([] {
+    Ts s;
+    (^Ts); // expected-error {{expected expression}}
+  }, ...);
+
+  [] { // expected-error {{unexpanded parameter pack 'Ts'}}
+    ^ { Ts s; return not_defined; }; // expected-error {{use of undeclared identifier 'not_defined'}}
+  };
+}