[clang-format] Don't format already formatted integer literals

[owenpan]

Summary

Fixes a bug in IntegerLiteralSeparatorFixer::checkSeparator() so that only unformatted integer literals will be formatted.

[MyDeveloperDay]

Do we have any unit tests for this that we can pump a shed load of examples at?

[owenpan]

In D146501#4209026, @MyDeveloperDay wrote:

Do we have any unit tests for this that we can pump a shed load of examples at?

I would need to make checkSeparator() public to add unit tests for it. Even then, the tests would be redundant to the added assertion (assert(Formatted != Text); on line 146), which would have caught the bug.

[owenpan]

Simplifies the fix.

[owenpan]

This patch is effectively NFC.

clang/lib/Format/IntegerLiteralSeparatorFixer.cpp

for (bool Skip = false; !Lex.LexFromRawLexer(Tok);) {
     }
     auto DigitsPerGroup = Decimal;
     if (IsBase2)
       DigitsPerGroup = Binary;
     else if (IsBase16)
       DigitsPerGroup = Hex;
     if (DigitsPerGroup > 0 && checkSeparator(Text, DigitsPerGroup))
       continue;
+    const auto &Formatted = format(Text, DigitsPerGroup);
+    assert(Formatted != Text);
     if (Start > 0)
       Location = Location.getLocWithOffset(Start);
-    if (const auto &Formatted = format(Text, DigitsPerGroup);
-        Formatted != Text) {
-      cantFail(Result.add(
-          tooling::Replacement(SourceMgr, Location, Length, Formatted)));
-    }
-  }
 
   return {Result, 0};
 }
 
 bool IntegerLiteralSeparatorFixer::checkSeparator(
     const StringRef IntegerLiteral, int DigitsPerGroup) const {
   assert(DigitsPerGroup > 0);
 
   int I = 0;
   for (auto C : llvm::reverse(IntegerLiteral)) {
     if (C == Separator) {
       if (I < DigitsPerGroup)
         return false;
       I = 0;
     } else {
-      ++I;
       if (I == DigitsPerGroup)
         return false;
+      ++I;
     }
   }
 
   return true;
 }
 
 std::string IntegerLiteralSeparatorFixer::format(const StringRef IntegerLiteral,
                                                  int DigitsPerGroup) const {