[clang-format] Fix a bug in wrapping function return type (#129374)

Fixes #113766

Author: owenca

clang/lib/Format/ContinuationIndenter.cpp

@@ -628,6 +628,10 @@ bool ContinuationIndenter::mustBreak(const LineState &State) {
       // name.
       !Style.isJavaScript() && Previous.isNot(tok::kw_template) &&
       CurrentState.BreakBeforeParameter) {
+    for (const auto *Tok = &Previous; Tok; Tok = Tok->Previous)
+      if (Tok->FirstAfterPPDirectiveLine || Tok->is(TT_LineComment))
+        return false;
+
     return true;
   }
 

clang/lib/Format/FormatToken.h

@@ -594,6 +594,9 @@ struct FormatToken {
   /// Has "\n\f\n" or "\n\f\r\n" before TokenText.
   bool HasFormFeedBefore = false;
 
+  /// Is the first token after a PPDirective line.
+  bool FirstAfterPPDirectiveLine = false;
+
   /// Number of optional braces to be inserted after this token:
   ///   -1: a single left brace
   ///    0: no braces

clang/lib/Format/UnwrappedLineParser.cpp

@@ -5091,8 +5091,10 @@ UnwrappedLineParser::parseMacroCall() {
 void UnwrappedLineParser::pushToken(FormatToken *Tok) {
   Line->Tokens.push_back(UnwrappedLineNode(Tok));
   if (MustBreakBeforeNextToken) {
-    Line->Tokens.back().Tok->MustBreakBefore = true;
-    Line->Tokens.back().Tok->MustBreakBeforeFinalized = true;
+    auto &Tok = *Line->Tokens.back().Tok;
+    Tok.MustBreakBefore = true;
+    Tok.MustBreakBeforeFinalized = true;
+    Tok.FirstAfterPPDirectiveLine = true;
     MustBreakBeforeNextToken = false;
   }
 }

clang/unittests/Format/FormatTest.cpp

@@ -6832,6 +6832,11 @@ TEST_F(FormatTest, LayoutStatementsAroundPreprocessorDirectives) {
                "                  param3) {\n"
                "  f();\n"
                "}");
+
+  verifyFormat("#ifdef __cplusplus\n"
+               "extern \"C\"\n"
+               "#endif\n"
+               "    void f();");
 }
 
 TEST_F(FormatTest, GraciouslyHandleIncorrectPreprocessorConditions) {
@@ -8539,6 +8544,7 @@ TEST_F(FormatTest, BreaksFunctionDeclarations) {
   verifyGoogleFormat(
       "SomeLoooooooooooooooooooooooooooooogType operator<<(\n"
       "    const SomeLooooooooogType &a, const SomeLooooooooogType &b);");
+
   verifyFormat("void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"
                "    int aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa = 1);");
   verifyFormat("aaaaaaaaaaaaaaaaaaaaaa\n"
@@ -8552,6 +8558,9 @@ TEST_F(FormatTest, BreaksFunctionDeclarations) {
                      "aaaaaaaaaaaaaaaaaaaaaaa<T>::aaaaaaaaaaaaa(\n"
                      "    aaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa);");
 
+  verifyFormat("extern \"C\" //\n"
+               "    void f();");
+
   FormatStyle Style = getLLVMStyle();
   Style.PointerAlignment = FormatStyle::PAS_Left;
   verifyFormat("void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"