[Sema] Use underlying type of scoped enum for -Wformat diagnostics (#67378)

Right now, `-Wformat` for a scoped enum will suggest a cast based on the
format specifier being used. This can lead to incorrect results, e.g.
attempting to format a scoped enum with `%s` would suggest casting to
`char *` instead of fixing the specifier. Change the logic to treat the
scoped enum's underlying type as the intended type to be printed, and
suggest format specifier changes and casts based on that.

1 files changed, 12 insertions, 13 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 0b9bee4..3b0cc15 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -11356,12 +11356,15 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
       ImplicitMatch == ArgType::NoMatchTypeConfusion)
     Match = ImplicitMatch;
   assert(Match != ArgType::MatchPromotion);
+
   // Look through unscoped enums to their underlying type.
   bool IsEnum = false;
   bool IsScopedEnum = false;
+  QualType IntendedTy = ExprTy;
   if (auto EnumTy = ExprTy->getAs<EnumType>()) {
+    IntendedTy = EnumTy->getDecl()->getIntegerType();
     if (EnumTy->isUnscopedEnumerationType()) {
-      ExprTy = EnumTy->getDecl()->getIntegerType();
+      ExprTy = IntendedTy;
       // This controls whether we're talking about the underlying type or not,
       // which we only want to do when it's an unscoped enum.
       IsEnum = true;
@@ -11373,7 +11376,6 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
   // %C in an Objective-C context prints a unichar, not a wchar_t.
   // If the argument is an integer of some kind, believe the %C and suggest
   // a cast instead of changing the conversion specifier.
-  QualType IntendedTy = ExprTy;
   if (isObjCContext() &&
       FS.getConversionSpecifier().getKind() == ConversionSpecifier::CArg) {
     if (ExprTy->isIntegralOrUnscopedEnumerationType() &&
@@ -11409,8 +11411,10 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
     std::tie(CastTy, CastTyName) = shouldNotPrintDirectly(S.Context, IntendedTy, E);
     if (!CastTy.isNull()) {
       // %zi/%zu and %td/%tu are OK to use for NSInteger/NSUInteger of type int
-      // (long in ASTContext). Only complain to pedants.
-      if ((CastTyName == "NSInteger" || CastTyName == "NSUInteger") &&
+      // (long in ASTContext). Only complain to pedants or when they're the
+      // underlying type of a scoped enum (which always needs a cast).
+      if (!IsScopedEnum &&
+          (CastTyName == "NSInteger" || CastTyName == "NSUInteger") &&
           (AT.isSizeT() || AT.isPtrdiffT()) &&
           AT.matchesType(S.Context, CastTy))
         Match = ArgType::NoMatchPedantic;
@@ -11465,20 +11469,15 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
       // should be printed as 'long' for 64-bit compatibility.)
       // Rather than emitting a normal format/argument mismatch, we want to
       // add a cast to the recommended type (and correct the format string
-      // if necessary).
+      // if necessary). We should also do so for scoped enumerations.
       SmallString<16> CastBuf;
       llvm::raw_svector_ostream CastFix(CastBuf);
       CastFix << (S.LangOpts.CPlusPlus ? "static_cast<" : "(");
-      if (IsScopedEnum) {
-        CastFix << AT.getRepresentativeType(S.Context).getAsString(
-            S.Context.getPrintingPolicy());
-      } else {
-        IntendedTy.print(CastFix, S.Context.getPrintingPolicy());
-      }
+      IntendedTy.print(CastFix, S.Context.getPrintingPolicy());
       CastFix << (S.LangOpts.CPlusPlus ? ">" : ")");
 
       SmallVector<FixItHint,4> Hints;
-      if ((!AT.matchesType(S.Context, IntendedTy) && !IsScopedEnum) ||
+      if (AT.matchesType(S.Context, IntendedTy) != ArgType::Match ||
           ShouldNotPrintDirectly)
         Hints.push_back(FixItHint::CreateReplacement(SpecRange, os.str()));
 
@@ -11506,7 +11505,7 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
         Hints.push_back(FixItHint::CreateInsertion(After, ")"));
       }
 
-      if (ShouldNotPrintDirectly) {
+      if (ShouldNotPrintDirectly && !IsScopedEnum) {
         // The expression has a type that should not be printed directly.
         // We extract the name from the typedef because we don't want to show
         // the underlying type in the diagnostic.