[clang-doc] remove default label on some switches (#143919)

LLVM style prefers no default label on fully covered switches to warn if
new enums are added. This patch removes the default label for that
purpose or uses IT_default instead of default if that was the only enum
not covered.

clang-tools-extra/clang-doc/BitcodeReader.cpp

@@ -54,10 +54,8 @@ static llvm::Error decodeRecord(const Record &R, AccessSpecifier &Field,
   case AS_none:
     Field = (AccessSpecifier)R[0];
     return llvm::Error::success();
-  default:
-    return llvm::createStringError(llvm::inconvertibleErrorCode(),
-                                   "invalid value for AccessSpecifier");
   }
+  llvm_unreachable("invalid value for AccessSpecifier");
 }
 
 static llvm::Error decodeRecord(const Record &R, TagTypeKind &Field,

clang-tools-extra/clang-doc/BitcodeWriter.cpp

@@ -664,7 +664,7 @@ bool ClangDocBitcodeWriter::dispatchInfoForWrite(Info *I) {
   case InfoType::IT_typedef:
     emitBlock(*static_cast<clang::doc::TypedefInfo *>(I));
     break;
-  default:
+  case InfoType::IT_default:
     llvm::errs() << "Unexpected info, unable to write.\n";
     return true;
   }

clang-tools-extra/clang-doc/Representation.cpp

@@ -143,7 +143,7 @@ mergeInfos(std::vector<std::unique_ptr<Info>> &Values) {
     return reduce<FunctionInfo>(Values);
   case InfoType::IT_typedef:
     return reduce<TypedefInfo>(Values);
-  default:
+  case InfoType::IT_default:
     return llvm::createStringError(llvm::inconvertibleErrorCode(),
                                    "unexpected info type");
   }

clang-tools-extra/clang-doc/Serialize.cpp

@@ -388,7 +388,8 @@ std::string serialize(std::unique_ptr<Info> &I) {
     return serialize(*static_cast<EnumInfo *>(I.get()));
   case InfoType::IT_function:
     return serialize(*static_cast<FunctionInfo *>(I.get()));
-  default:
+  case InfoType::IT_typedef:
+  case InfoType::IT_default:
     return "";
   }
 }
@@ -525,9 +526,13 @@ static std::unique_ptr<Info> makeAndInsertIntoParent(ChildType Child) {
     InsertChild(ParentRec->Children, std::forward<ChildType>(Child));
     return ParentRec;
   }
-  default:
-    llvm_unreachable("Invalid reference type for parent namespace");
+  case InfoType::IT_default:
+  case InfoType::IT_enum:
+  case InfoType::IT_function:
+  case InfoType::IT_typedef:
+    break;
   }
+  llvm_unreachable("Invalid reference type for parent namespace");
 }
 
 // There are two uses for this function.

clang-tools-extra/unittests/clang-doc/BitcodeTest.cpp

@@ -37,7 +37,7 @@ static std::string writeInfo(Info *I) {
     return writeInfo(*static_cast<FunctionInfo *>(I));
   case InfoType::IT_typedef:
     return writeInfo(*static_cast<TypedefInfo *>(I));
-  default:
+  case InfoType::IT_default:
     return "";
   }
 }