From bf7e2b81e779713cc535c884e287ec6cf02fcfef Mon Sep 17 00:00:00 2001
From: Oleksandr Tarasiuk <oleksandr.tarasiuk@outlook.com>
Date: Wed, 28 Jan 2026 15:44:48 +0200
Subject: [PATCH] [Clang] prevent preprocessor crash on incomplete scoped
 __has_cpp_attribute arguments (#178273)

Fixes #178098

---

This patch addressed the issue when `__has_cpp_attribute` is expanded
with incomplete scoped attributes. The scoped name parsing can lex to
`eof`/`eod` at


https://github.com/llvm/llvm-project/blob/3f5a5d45d18a514f086f3e07c9676ca5fb95bbe9/clang/lib/Lex/PPMacroExpansion.cpp#L1877-L1881

and then proceed with


https://github.com/llvm/llvm-project/blob/3f5a5d45d18a514f086f3e07c9676ca5fb95bbe9/clang/lib/Lex/PPMacroExpansion.cpp#L1425-L1430


since `eof`/`eod` is not guarded at


https://github.com/llvm/llvm-project/blob/3f5a5d45d18a514f086f3e07c9676ca5fb95bbe9/clang/lib/Lex/PPMacroExpansion.cpp#L1367-L1372

this could lead to a preprocessor crash


https://github.com/llvm/llvm-project/blob/3f5a5d45d18a514f086f3e07c9676ca5fb95bbe9/clang/lib/Lex/PPMacroExpansion.cpp#L1370
---
 clang/docs/ReleaseNotes.rst                     |  1 +
 clang/lib/Lex/PPMacroExpansion.cpp              |  4 ++--
 .../test/Preprocessor/has_attribute_errors.cpp  | 17 +++++++++++++++++
 .../test/Preprocessor/has_c_attribute_errors.c  |  9 +++++++++
 4 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Preprocessor/has_c_attribute_errors.c

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index b5327c01fbb8..42a300ca9458 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -210,6 +210,7 @@ Bug Fixes in This Version
 - Fixed a failed assertion in the preprocessor when ``__has_embed`` parameters are missing parentheses. (#GH175088)
 
 - Fix lifetime extension of temporaries in for-range-initializers in templates. (#GH165182)
+- Fixed a preprocessor crash in ``__has_cpp_attribute`` on incomplete scoped attributes. (#GH178098)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 5efa4b5b3f87..350bd6c88eaa 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -1364,7 +1364,7 @@ static void EvaluateFeatureLikeBuiltinMacro(llvm::raw_svector_ostream& OS,
 
   Token ResultTok;
   bool SuppressDiagnostic = false;
-  while (true) {
+  while (Tok.isNoneOf(tok::eod, tok::eof)) {
     // Parse next token.
     if (ExpandArgs)
       PP.Lex(Tok);
@@ -1443,7 +1443,7 @@ already_lexed:
       PP.Diag(LParenLoc, diag::note_matching) << tok::l_paren;
       SuppressDiagnostic = true;
     }
-  }
+}
 }
 
 /// Helper function to return the IdentifierInfo structure of a Token
diff --git a/clang/test/Preprocessor/has_attribute_errors.cpp b/clang/test/Preprocessor/has_attribute_errors.cpp
index 1fc88d3f926f..199227e90f05 100644
--- a/clang/test/Preprocessor/has_attribute_errors.cpp
+++ b/clang/test/Preprocessor/has_attribute_errors.cpp
@@ -14,3 +14,20 @@ __has_cpp_attribute(__clang__::fallthrough) // expected-error {{missing ')' afte
                                             // expected-note {{to match this '('}} \
                                             // expected-error {{builtin feature check macro requires a parenthesized identifier}}
 
+namespace GH178098 {
+// expected-error@+2 {{builtin feature check macro requires a parenthesized identifier}}
+// expected-error@+1 {{expected value in expression}}
+#if __has_cpp_attribute(clang::
+#endif
+
+// expected-error@+4 {{unterminated function-like macro invocation}}
+// expected-error@+3 {{missing ')' after 'clang'}}
+// expected-error@+2 {{expected value in expression}}
+// expected-note@+1 {{to match this '('}}
+#if __has_attribute(clang::
+#endif
+
+// expected-error@+3 {{builtin feature check macro requires a parenthesized identifier}}
+// expected-error@+2 {{unterminated function-like macro invocation}}
+__has_cpp_attribute(clang::
+}
diff --git a/clang/test/Preprocessor/has_c_attribute_errors.c b/clang/test/Preprocessor/has_c_attribute_errors.c
new file mode 100644
index 000000000000..026c0bd37e7f
--- /dev/null
+++ b/clang/test/Preprocessor/has_c_attribute_errors.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown -Eonly -verify %s
+
+// expected-error@+2 {{builtin feature check macro requires a parenthesized identifier}}
+// expected-error@+1 {{expected value in expression}}
+#if __has_c_attribute(clang::
+#endif
+
+// expected-error@+1 {{builtin feature check macro requires a parenthesized identifier}}
+__has_c_attribute(clang::