[Clang] Recurse into parsing when using pack-indexing as a specifier

[zyn0217]

Pack indexing type that introduces a scope, e.g. T...[0]::value would be annotated as annot_cxxscope. This is something we didn't handle in ParseCastExpression, causing it to mistakely fall through to the logic for raw_identifier.

We should recurse into parsing the following specifiers for such cases.

Closes #119072

[llvmbot]

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

Changes

Closes #119072

---

Full diff: https://github.com/llvm/llvm-project/pull/119123.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+1)
• (modified) clang/lib/Parse/ParseExpr.cpp (+1-1)
• (modified) clang/test/Parser/cxx2c-pack-indexing.cpp (+9)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 20bd27ad52f577..57fcca04fc53ca 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -763,6 +763,7 @@ Bug Fixes to C++ Support
 - Fixed a bug where bounds of partially expanded pack indexing expressions were checked too early. (#GH116105)
 - Fixed an assertion failure caused by using ``consteval`` in condition in consumed analyses. (#GH117385)
 - Fix a crash caused by incorrect argument position in merging deduced template arguments. (#GH113659)
+- Fixed a parser crash when using pack indexing as a nested name specifier. (#GH119072) 
 - Fixed an assertion failure caused by mangled names with invalid identifiers. (#GH112205)
 
 Bug Fixes to AST Handling
diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index 736484ded8383c..8dd72db8f5b4a2 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -1199,7 +1199,7 @@ ExprResult Parser::ParseCastExpression(CastParseKind ParseKind,
         // If the token is not annotated, then it might be an expression pack
         // indexing
         if (!TryAnnotateTypeOrScopeToken() &&
-            Tok.is(tok::annot_pack_indexing_type))
+            Tok.isOneOf(tok::annot_pack_indexing_type, tok::annot_cxxscope))
           return ParseCastExpression(ParseKind, isAddressOfOperand, isTypeCast,
                                      isVectorLiteral, NotPrimaryExpression);
       }
diff --git a/clang/test/Parser/cxx2c-pack-indexing.cpp b/clang/test/Parser/cxx2c-pack-indexing.cpp
index c279bdd7af8c44..99347a2f8f1571 100644
--- a/clang/test/Parser/cxx2c-pack-indexing.cpp
+++ b/clang/test/Parser/cxx2c-pack-indexing.cpp
@@ -74,3 +74,12 @@ struct SS {
     }
 };
 }
+
+namespace GH119072 {
+
+template<typename... Ts>
+void foo() {
+  decltype(Ts...[0]::t) value;
+}
+
+}

[cor3ntin]

the commit message could use more details, otherwise LGTM.
Thanks for fixing that