[clang][Diags] Automatically format AP(S)Int values with separators (#161047)

This adds an `operator<<` overload for `StreamingDiagnostic` that takes
an `APInt`/`APSInt` and formats it with default options, including
adding separators.

This is still an opt-in mechanism since all callers that want to use
this feature need to be changed from

```c++
  Diag() << toString(MyInt, 10);
```

to

```c++
  Diag() << MyInt;
```

This patch contains one example of a diagnostic making use of this.

Author: tbaederr

clang/include/clang/Basic/Diagnostic.h

@@ -25,6 +25,7 @@
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Compiler.h"
 #include <cassert>
@@ -1366,6 +1367,22 @@ inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
   return DB;
 }
 
+inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
+                                             const llvm::APSInt &Int) {
+  DB.AddString(toString(Int, /*Radix=*/10, Int.isSigned(),
+                        /*formatAsCLiteral=*/false,
+                        /*UpperCase=*/true, /*InsertSeparators=*/true));
+  return DB;
+}
+
+inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
+                                             const llvm::APInt &Int) {
+  DB.AddString(toString(Int, /*Radix=*/10, /*Signed=*/false,
+                        /*formatAsCLiteral=*/false,
+                        /*UpperCase=*/true, /*InsertSeparators=*/true));
+  return DB;
+}
+
 inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
                                              int I) {
   DB.AddTaggedVal(I, DiagnosticsEngine::ak_sint);

clang/lib/Sema/SemaDecl.cpp

@@ -18909,8 +18909,7 @@ ExprResult Sema::VerifyBitField(SourceLocation FieldLoc,
     // 'bool'.
     if (BitfieldIsOverwide && !FieldTy->isBooleanType() && FieldName) {
       Diag(FieldLoc, diag::warn_bitfield_width_exceeds_type_width)
-          << FieldName << toString(Value, 10)
-          << (unsigned)TypeWidth;
+          << FieldName << Value << (unsigned)TypeWidth;
     }
   }
 

clang/test/SemaCXX/bitfield-layout.cpp

@@ -35,7 +35,7 @@ CHECK_SIZE(Test4, 8);
 CHECK_ALIGN(Test4, 8);
 
 struct Test5 {
-  char c : 0x100000001; // expected-warning {{width of bit-field 'c' (4294967297 bits) exceeds the width of its type; value will be truncated to 8 bits}}
+  char c : 0x100000001; // expected-warning {{width of bit-field 'c' (4'294'967'297 bits) exceeds the width of its type; value will be truncated to 8 bits}}
 };
 // Size and align don't really matter here, just make sure we don't crash.
 CHECK_SIZE(Test5, 1);