[clang-format] fix PR38557 - comments between "default" and ':' causes the case label to be treated as an identifier

[owenpan]

Summary

The Bug was reported and fixed by Owen Pan. See the original bug report here: https://bugs.llvm.org/show_bug.cgi?id=38557

Patch by Owen Pan!

[JonasToth]

Using git for the diff, add testcase

[owenpan]

Updated the test case.

[klimek]

lg

lib/Format/UnwrappedLineParser.cpp

do {
     case tok::r_brace:
       if (HasOpeningBrace)
         return;
       nextToken();
       addUnwrappedLine();
       break;
     case tok::kw_default: {
       unsigned StoredPosition = Tokens->getPosition();
-      FormatToken *Next = Tokens->getNextToken();
+      FormatToken *Next;
+      do {
+        Next = Tokens->getNextToken();
+      } while (Next && Next->is(tok::comment));
       FormatTok = Tokens->setPosition(StoredPosition);
       if (Next && Next->isNot(tok::colon)) {
         // default not followed by ':' is not a case label; treat it like
         // an identifier.
         parseStructuralElement();
         break;
       }
       // Else, if it is 'default:', fall through to the case handling.

unittests/Format/FormatTest.cpp

verifyFormat("switch (a) {\n"
                "case 3:\n"
                "case 4:\n"
                "case 5: return;\n"
                "default:\n"
                "  y = 1;\n"
                "  break;\n"
                "}",
                Style);
+  Style.ColumnLimit = 80;
+  Style.AllowShortCaseLabelsOnASingleLine = false;
+  Style.IndentCaseLabels = true;
+  EXPECT_EQ("switch (n) {\n"
+            "  default /*comments*/:\n"
+            "    return true;\n"
+            "  case 0:\n"
+            "    return false;\n"
+            "}",
+            format("switch (n) {\n"
+                   "default/*comments*/:\n"
+                   "  return true;\n"
+                   "case 0:\n"
+                   "  return false;\n"
+                   "}",
+                   Style));
 }
 
 TEST_F(FormatTest, FormatsLabels) {
   verifyFormat("void f() {\n"
                "  some_code();\n"
                "test_label:\n"
                "  some_other_code();\n"
                "  {\n"