[clang] Don't crash when -Wformat-signedness specified

clang/docs/ReleaseNotes.rst

@@ -440,6 +440,7 @@ Bug Fixes to C++ Support
   ``__builtin_addressof``, and related issues with builtin arguments. (#GH154034)
 - Fix an assertion failure when taking the address on a non-type template parameter argument of
   object type. (#GH151531)
+- Fix an assertion failure of format string signedness check when ``-Wformat-signedness`` (#GH161075).
 - Suppress ``-Wdouble-promotion`` when explicitly asked for with C++ list initialization (#GH33409).
 - Fix the result of `__builtin_is_implicit_lifetime` for types with a user-provided constructor. (#GH160610)
 - Correctly deduce return types in ``decltype`` expressions. (#GH160497) (#GH56652) (#GH116319) (#GH161196)

clang/lib/Sema/SemaChecking.cpp

@@ -8811,8 +8811,10 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
       case ArgType::Match:
       case ArgType::MatchPromotion:
       case ArgType::NoMatchPromotionTypeConfusion:
-      case ArgType::NoMatchSignedness:
         llvm_unreachable("expected non-matching");
+      case ArgType::NoMatchSignedness:
+        Diag = diag::warn_format_conversion_argument_type_mismatch_signedness;
+        break;
       case ArgType::NoMatchPedantic:
         Diag = diag::warn_format_conversion_argument_type_mismatch_pedantic;
         break;

clang/test/Sema/format-strings-signedness.cpp

@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only -verify -Wformat -Wformat-signedness %s
+// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only -verify -Wformat -Wformat-signedness %s
+
+// Verify that -Wformat-signedness alone (without -Wformat) trigger the
+// warnings. Note in gcc this will not trigger the signedness warnings as
+// -Wformat is default off in gcc.
+// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only -verify -Wformat-signedness %s
+// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only -verify -Wformat-signedness %s
+
+// Verify that -Wformat-signedness warnings are not reported with only -Wformat
+// (gcc compat).
+// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only -Wformat -verify=okay %s
+
+// Verify that -Wformat-signedness with -Wno-format are not reported (gcc compat).
+// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only -Wformat-signedness -Wno-format -verify=okay %s
+// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only -Wno-format -Wformat-signedness -verify=okay %s
+// okay-no-diagnostics
+
+// Ignore 'GCC requires a function with the 'format' attribute to be variadic'.
+#pragma GCC diagnostic ignored "-Wgcc-compat"
+namespace GH161075 {
+template <typename... Args>
+void format(const char *fmt, Args &&...args)
+    __attribute__((format(printf, 1, 2)));
+
+void do_format() {
+  bool b = false;
+  format("%hhi %hhu %hi %hu %i %u", b, b, b, b, b, b);  // expected-warning {{format specifies type 'unsigned char' but the argument has type 'bool', which differs in signedness}}
+}
+} // namespace GH161075