[clang-format] Restrict the special handling for K&R C to C/C++

[owenpan]

Summary

Commits 58494c856a15, f6bc614546e1, and 0fc27ef19670 added special handlings for K&R C function definitions and caused some JavaScript/TypeScript regressions which were addressed in D107267, D108538, and D108620. This patch could have prevented these known regressions and will fix any unknown ones.

clang/lib/Format/TokenAnnotator.cpp

else if (Line.startsWith(TT_ObjCProperty))
     Line.Type = LT_ObjCProperty;
 
   Line.First->SpacesRequiredBefore = 1;
   Line.First->CanBreakBefore = Line.First->MustBreakBefore;
 }
 
 // This function heuristically determines whether 'Current' starts the name of a
 // function declaration.
-static bool isFunctionDeclarationName(const FormatToken &Current,
+static bool isFunctionDeclarationName(bool IsCpp, const FormatToken &Current,
                                       const AnnotatedLine &Line) {
   auto skipOperatorName = [](const FormatToken *Next) -> const FormatToken * {
     for (; Next; Next = Next->Next) {
       if (Next->is(TT_OverloadedOperatorLParen))
         return Next;
       if (Next->is(TT_OverloadedOperator))
         continue;
       if (Next->isOneOf(tok::kw_new, tok::kw_delete)) {
static bool isFunctionDeclarationName(bool IsCpp, const FormatToken &Current,
   if (Line.Last->is(tok::l_brace))
     return true;
   if (Next->Next == Next->MatchingParen)
     return true; // Empty parentheses.
   // If there is an &/&& after the r_paren, this is likely a function.
   if (Next->MatchingParen->Next &&
       Next->MatchingParen->Next->is(TT_PointerOrReference))
     return true;
-  // Check for K&R C function definitions, e.g.:
+
+  // Check for K&R C function definitions (and C++ function definitions with
+  // unnamed parameters), e.g.:
   //   int f(i)
   //   {
   //     return i + 1;
   //   }
-  if (Next->Next && Next->Next->is(tok::identifier) &&
+  //   bool g(size_t = 0, bool b = false)
+  //   {
+  //     return !b;
+  //   }
+  if (IsCpp && Next->Next && Next->Next->is(tok::identifier) &&
       !Line.endsWith(tok::semi))
     return true;
+
   for (const FormatToken *Tok = Next->Next; Tok && Tok != Next->MatchingParen;
        Tok = Tok->Next) {
     if (Tok->is(TT_TypeDeclarationParen))
       return true;
     if (Tok->isOneOf(tok::l_paren, TT_TemplateOpener) && Tok->MatchingParen) {
       Tok = Tok->MatchingParen;
       continue;
     }
void TokenAnnotator::calculateFormattingInformation(AnnotatedLine &Line) {
   bool InFunctionDecl = Line.MightBeFunctionDecl;
   bool AlignArrayOfStructures =
       (Style.AlignArrayOfStructures != FormatStyle::AIAS_None &&
        Line.Type == LT_ArrayOfStructInitializer);
   if (AlignArrayOfStructures)
     calculateArrayInitializerColumnList(Line);
 
   while (Current) {
-    if (isFunctionDeclarationName(*Current, Line))
+    if (isFunctionDeclarationName(Style.isCpp(), *Current, Line))
       Current->setType(TT_FunctionDeclarationName);
     if (Current->is(TT_LineComment)) {
       if (Current->Previous->is(BK_BracedInit) &&
           Current->Previous->opensScope())
         Current->SpacesRequiredBefore =
             (Style.Cpp11BracedListStyle && !Style.SpacesInParentheses) ? 0 : 1;
       else
         Current->SpacesRequiredBefore = Style.SpacesBeforeTrailingComments;

clang/unittests/Format/FormatTest.cpp

verifyFormat("byte *\n" // Break here.
                Style);
   verifyFormat("bool f(int a, int) override;\n"
                "Bar g(int a, Bar) final;\n"
                "Bar h(a, Bar) final;",
                Style);
   verifyFormat("int\n"
                "f(a)",
                Style);
+  verifyFormat("bool\n"
+               "f(size_t = 0, bool b = false)\n"
+               "{\n"
+               "  return !b;\n"
+               "}",
+               Style);
 
   // The return breaking style doesn't affect:
   // * function and object definitions with attribute-like macros
   verifyFormat("Tttttttttttttttttttttttt ppppppppppppppp\n"
                "    ABSL_GUARDED_BY(mutex) = {};",
                getGoogleStyleWithColumns(40));
   verifyFormat("Tttttttttttttttttttttttt ppppppppppppppp\n"
                "    ABSL_GUARDED_BY(mutex);  // comment",