[clang][Sema] Add fixit for scoped enum format error

This helps transition code bases to handle the new warning added in 3632e2f

Before:
```
clang/test/FixIt/format.cpp:10:16: warning: format specifies type 'int' but the argument has type 'N::E' [-Wformat]
   10 |   printf("%d", N::E::One); // expected-warning{{format specifies type 'int' but the argument has type 'N::E'}}
      |           ~~   ^~~~~~~~~
      |           %d
```
After:
```
clang/test/FixIt/format.cpp:10:16: warning: format specifies type 'int' but the argument has type 'N::E' [-Wformat]
   10 |   printf("%d", N::E::One); // expected-warning{{format specifies type 'int' but the argument has type 'N::E'}}
      |           ~~   ^~~~~~~~~
      |                static_cast<int>( )
```

Differential Revision: https://reviews.llvm.org/D153623

Author: abrachet

clang/docs/ReleaseNotes.rst

@@ -417,6 +417,9 @@ Improvements to Clang's diagnostics
          ^            ~~~~~~
 - ``-Wformat`` cast fix-its will now suggest ``static_cast`` instead of C-style casts
   for C++ code.
+- ``-Wformat`` will no longer suggest a no-op fix-it for fixing scoped enum format
+  warnings. Instead, it will suggest casting the enum object to the type specified
+  in the format string.
 
 Bug Fixes in This Version
 -------------------------

clang/lib/Sema/SemaChecking.cpp

@@ -11077,12 +11077,15 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
   assert(Match != ArgType::MatchPromotion);
   // Look through unscoped enums to their underlying type.
   bool IsEnum = false;
+  bool IsScopedEnum = false;
   if (auto EnumTy = ExprTy->getAs<EnumType>()) {
     if (EnumTy->isUnscopedEnumerationType()) {
       ExprTy = EnumTy->getDecl()->getIntegerType();
       // 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;
+    } else {
+      IsScopedEnum = true;
     }
   }
 
@@ -11148,7 +11151,7 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
 
     CharSourceRange SpecRange = getSpecifierRange(StartSpecifier, SpecifierLen);
 
-    if (IntendedTy == ExprTy && !ShouldNotPrintDirectly) {
+    if (IntendedTy == ExprTy && !ShouldNotPrintDirectly && !IsScopedEnum) {
       unsigned Diag;
       switch (Match) {
       case ArgType::Match:
@@ -11185,11 +11188,17 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
       SmallString<16> CastBuf;
       llvm::raw_svector_ostream CastFix(CastBuf);
       CastFix << (S.LangOpts.CPlusPlus ? "static_cast<" : "(");
-      IntendedTy.print(CastFix, S.Context.getPrintingPolicy());
+      if (IsScopedEnum) {
+        CastFix << AT.getRepresentativeType(S.Context).getAsString(
+            S.Context.getPrintingPolicy());
+      } else {
+        IntendedTy.print(CastFix, S.Context.getPrintingPolicy());
+      }
       CastFix << (S.LangOpts.CPlusPlus ? ">" : ")");
 
       SmallVector<FixItHint,4> Hints;
-      if (!AT.matchesType(S.Context, IntendedTy) || ShouldNotPrintDirectly)
+      if ((!AT.matchesType(S.Context, IntendedTy) && !IsScopedEnum) ||
+          ShouldNotPrintDirectly)
         Hints.push_back(FixItHint::CreateReplacement(SpecRange, os.str()));
 
       if (const CStyleCastExpr *CCast = dyn_cast<CStyleCastExpr>(E)) {

clang/test/FixIt/format.cpp

@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -fsyntax-only -fdiagnostics-parseable-fixits -Wformat %s 2>&1 | FileCheck %s
+
+extern "C" int printf(const char *, ...);
+
+namespace N {
+  enum class E { One };
+}
+
+void a() {
+  printf("%d", N::E::One); // expected-warning{{format specifies type 'int' but the argument has type 'N::E'}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:16-[[@LINE-1]]:16}:"static_cast<int>("
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-2]]:25-[[@LINE-2]]:25}:")"
+
+  printf("%hd", N::E::One);
+  // CHECK: "static_cast<short>("
+
+  printf("%hu", N::E::One);
+  // CHECK: "static_cast<unsigned short>("
+}