[flang] [compiler-rt] [libunwind] [libcxx] [clang] [lld] [clang-tools-extra] [lldb] [libc] [llvm] Fix clang to recognize new C23 modifiers %w and %wf when printing (PR #71771)

[Aaron Ballman via cfe-commits]

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@@ -286,7 +286,33 @@ clang::analyze_format_string::ParseLengthModifier(FormatSpecifier &FS,
       lmKind = LengthModifier::AsInt3264;
       break;
     case 'w':
-      lmKind = LengthModifier::AsWide; ++I; break;
+      ++I;
+      if (I == E) return false;
+      if (*I == 'f') {
+        lmKind = LengthModifier::AsWideFast;
+        ++I;
+      } else {
+        lmKind = LengthModifier::AsWide;
+      }
+
+      if (I == E) return false;
+      int s = 0;
+      while (unsigned(*I - '0') <= 9) {
+        s = 10 * s + unsigned(*I - '0');
+        ++I;
+      }
+
+      // s == 0 is MSVCRT case, like l but only for c, C, s, S, or Z on windows
+      // s != 0 for b, d, i, o, u, x, or X when a size followed(like 8, 16, 32 or 64)
+      if (s != 0) {
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AaronBallman wrote:

Should we return false in the case `s == 0`?

It would be good to add test coverage for parsing failures.

https://github.com/llvm/llvm-project/pull/71771