- fixed most of implicit fallthrough compilation warnings

src/common/console/c_console.cpp:1032:4: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/common/console/c_console.cpp:958:4: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/common/scripting/backend/codegen.cpp:2969:4: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/common/scripting/frontend/zcc_compile.cpp:2656:4: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/common/scripting/frontend/zcc_compile.cpp:521:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/common/scripting/jit/jit_math.cpp:966:19: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/d_main.cpp:1538:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/d_main.cpp:1549:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/d_main.cpp:3820:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/gameconfigfile.cpp:544:25: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/gamedata/p_xlat.cpp:193:11: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/gamedata/p_xlat.cpp:200:11: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/gamedata/p_xlat.cpp:210:11: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/g_game.cpp:1145:20: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/maploader/maploader.cpp:2142:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/menu/doommenu.cpp:159:28: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/m_cheat.cpp:109:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/mapthinkers/a_ceiling.cpp:254:24: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/mapthinkers/a_floor.cpp:322:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/mapthinkers/a_floor.cpp:330:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/mapthinkers/a_floor.cpp:344:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/mapthinkers/a_plats.cpp:129:47: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/mapthinkers/a_plats.cpp:284:8: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/p_acs.cpp:6302:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/p_acs.cpp:8111:16: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/playsim/p_spec.cpp:344:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/scripting/decorate/thingdef_parse.cpp:1343:9: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/scripting/zscript/zcc_compile_doom.cpp:298:12: warning: this statement may fall through [-Wimplicit-fallthrough=]
src/wi_stuff.cpp:463:14: warning: this statement may fall through [-Wimplicit-fallthrough=]

src/common/console/c_console.cpp

@@ -968,6 +968,7 @@ static bool C_HandleKey (event_t *ev, FCommandBuffer &buffer)
 				break;
 			}
 			// Intentional fall-through for command(s) added with Ctrl-D
+			[[fallthrough]];
 
 		case '\r':
 		{
@@ -1033,6 +1034,7 @@ static bool C_HandleKey (event_t *ev, FCommandBuffer &buffer)
 			{
 				break;
 			}
+			[[fallthrough]];
 		case GK_ESCAPE:
 			// Close console and clear command line. But if we're in the
 			// fullscreen console mode, there's nothing to fall back on

src/common/scripting/backend/codegen.cpp

@@ -2967,6 +2967,7 @@ FxExpression *FxMulDiv::Resolve(FCompileContext& ctx)
 		case '/':
 			// For division, the vector must be the first operand.
 			if (right->IsVector()) goto error;
+			[[fallthrough]];
 
 		case '*':
 			if (left->IsVector() && right->IsNumeric())

src/common/scripting/frontend/zcc_compile.cpp

@@ -523,6 +523,7 @@ ZCCCompiler::ZCCCompiler(ZCC_AST &ast, DObject *_outer, PSymbolTable &_symbols,
 					ProcessStruct(static_cast<ZCC_Struct*>(node), tnode, nullptr);
 					break;
 				}
+				goto common;
 
 			common:
 			case AST_ConstantDef:
@@ -2655,6 +2656,7 @@ FxExpression *ZCCCompiler::ConvertNode(ZCC_TreeNode *ast, bool substitute)
 				}
 			}
 			// fall through if this isn't an array access node.
+			[[fallthrough]];
 
 		default:
 			Error(fcall, "Invalid function identifier");

src/common/scripting/jit/jit_math.cpp

@@ -963,7 +963,7 @@ void JitCompiler::EmitFLOP()
 		FuncPtr func = nullptr;
 		switch (C)
 		{
-		default: I_Error("Unknown OP_FLOP subfunction");
+		default: I_Error("Unknown OP_FLOP subfunction"); break;
 		case FLOP_ABS:		func = fabs; break;
 		case FLOP_EXP:		func = g_exp; break;
 		case FLOP_LOG:		func = g_log; break;

src/d_main.cpp

@@ -1543,6 +1543,7 @@ void D_DoAdvanceDemo (void)
 			break;
 		}
 		// fall through to case 1 if no advisory notice
+		[[fallthrough]];
 
 	case 1:
 		Advisory = NULL;
@@ -1564,6 +1565,7 @@ void D_DoAdvanceDemo (void)
 				break;
 			}
 		}
+		[[fallthrough]];
 
 	default:
 	case 0:
@@ -3822,6 +3824,7 @@ void I_UpdateWindowTitle()
 			titlestr.Format("%s - %s", level.LevelName.GetChars(), GameStartupInfo.Name.GetChars());
 			break;
 		}
+		[[fallthrough]];
 	case 2:
 		titlestr = GameStartupInfo.Name;
 		break;

src/g_game.cpp

@@ -1143,6 +1143,7 @@ void G_Ticker ()
 			G_CheckDemoStatus();
 			G_RecordDemo(newdemoname);
 			G_BeginRecording(newdemomap);
+			[[fallthrough]];
 		case ga_newgame2:	// Silence GCC (see above)
 		case ga_newgame:
 			G_DoNewGame ();

src/gameconfigfile.cpp

@@ -542,6 +542,7 @@ void FGameConfigFile::DoGlobalSetup ()
 					case 1:
 						newvalue.Int = 0;
 						var->SetGenericRep(newvalue, CVAR_Int);
+						[[fallthrough]];
 					case 3:
 					case 4:
 						vid_scale_linear = true;

src/gamedata/p_xlat.cpp

@@ -191,6 +191,7 @@ void FLevelLocals::TranslateLineDef (line_t *ld, maplinedef_t *mld, int lineinde
 			{
 			case WalkMany:
 				flags |= ML_REPEAT_SPECIAL;
+				[[fallthrough]];
 			case WalkOnce:
 				ld->activation = SPAC_Cross;
 				break;
@@ -198,6 +199,7 @@ void FLevelLocals::TranslateLineDef (line_t *ld, maplinedef_t *mld, int lineinde
 			case SwitchMany:
 			case PushMany:
 				flags |= ML_REPEAT_SPECIAL;
+				[[fallthrough]];
 			case SwitchOnce:
 			case PushOnce:
 				if (passthrough)
@@ -208,6 +210,7 @@ void FLevelLocals::TranslateLineDef (line_t *ld, maplinedef_t *mld, int lineinde
 
 			case GunMany:
 				flags |= ML_REPEAT_SPECIAL;
+				[[fallthrough]];
 			case GunOnce:
 				ld->activation = SPAC_Impact;
 				break;

src/m_cheat.cpp

@@ -114,6 +114,7 @@ void cht_DoCheat (player_t *player, int cheat)
 			player->health = deh.GodHealth;
 		}
 		// fall through to CHT_GOD
+		[[fallthrough]];
 	case CHT_GOD:
 		player->cheats ^= CF_GODMODE;
 		if (player->cheats & CF_GODMODE)

src/maploader/maploader.cpp

@@ -2141,6 +2141,7 @@ void MapLoader::ProcessSideTextures(bool checktranmap, side_t *sd, sector_t *sec
 			break;
 		}
 		// Fallthrough for Hexen maps is intentional
+		[[fallthrough]];
 
 	default:			// normal cases
 

src/menu/doommenu.cpp

@@ -157,6 +157,7 @@ bool M_SetSpecialMenu(FName& menu, int param)
 		// sent either from skill menu or confirmation screen. Skill gets only set if sent from skill menu
 		// Now we can finally start the game. Ugh...
 		NewGameStartupInfo.Skill = param;
+		[[fallthrough]];
 	case NAME_StartgameConfirmed:
 
 		G_DeferedInitNew (&NewGameStartupInfo);

src/playsim/mapthinkers/a_ceiling.cpp

@@ -252,6 +252,7 @@ bool FLevelLocals::CreateCeiling(sector_t *sec, DCeiling::ECeiling type, line_t
 	case DCeiling::ceilCrushAndRaise:
 	case DCeiling::ceilCrushRaiseAndStay:
 		ceiling->m_TopHeight = sec->ceilingplane.fD();
+		[[fallthrough]];
 	case DCeiling::ceilLowerAndCrush:
 		targheight = FindHighestFloorPoint (sec, &spot);
 		targheight += height;

src/playsim/mapthinkers/a_floor.cpp

@@ -320,6 +320,7 @@ bool FLevelLocals::CreateFloor(sector_t *sec, DFloor::EFloor floortype, line_t *
 
 	case DFloor::floorLowerInstant:
 		floor->m_Speed = height;
+		[[fallthrough]];
 	case DFloor::floorLowerByValue:
 		floor->m_Direction = -1;
 		newheight = sec->CenterFloor() - height;
@@ -328,6 +329,7 @@ bool FLevelLocals::CreateFloor(sector_t *sec, DFloor::EFloor floortype, line_t *
 
 	case DFloor::floorRaiseInstant:
 		floor->m_Speed = height;
+		[[fallthrough]];
 	case DFloor::floorRaiseByValue:
 		floor->m_Direction = 1;
 		newheight = sec->CenterFloor() + height;
@@ -342,6 +344,7 @@ bool FLevelLocals::CreateFloor(sector_t *sec, DFloor::EFloor floortype, line_t *
 
 	case DFloor::floorRaiseAndCrushDoom:
 		height = 8;
+		[[fallthrough]];
 	case DFloor::floorRaiseToLowestCeiling:
 		floor->m_Direction = 1;
 		newheight = FindLowestCeilingSurrounding(sec, &spot) - height;

src/playsim/mapthinkers/a_plats.cpp

@@ -127,6 +127,7 @@ void DPlat::Tick ()
 						// better use a flag to avoid problems elsewhere. For example,
 						// keeping the thinker would make tagwait wait indefinitely.
 						m_Sector->planes[sector_t::floor].Flags |= PLANEF_BLOCKED; 
+						[[fallthrough]];
 					case platRaiseAndStay:
 					case platDownByValue:
 					case platDownWaitUpStay:
@@ -282,6 +283,7 @@ bool FLevelLocals::EV_DoPlat (int tag, line_t *line, DPlat::EPlatType type, doub
 		{
 		case DPlat::platToggle:
 			rtn = true;
+			[[fallthrough]];
 		case DPlat::platPerpetualRaise:
 			ActivateInStasisPlat (tag);
 			break;

src/playsim/p_acs.cpp

@@ -6299,7 +6299,7 @@ doplaysound:			if (funcIndex == ACSF_PlayActorSound)
 				int tid1 = 0, tid2 = 0;
 				switch (argCount)
 				{
-				case 4: tid2 = args[3];
+				case 4: tid2 = args[3]; [[fallthrough]];
 				case 3: tid1 = args[2];
 				}
 
@@ -8109,6 +8109,7 @@ int DLevelScript::RunScript()
 
 		case PCD_SETRESULTVALUE:
 			resultValue = STACK(1);
+			[[fallthrough]];
 		case PCD_DROP: //fall through.
 			sp--;
 			break;

src/playsim/p_spec.cpp

@@ -345,6 +345,7 @@ bool P_TestActivateLine (line_t *line, AActor *mo, int side, int activationType,
 					{
 						break;
 					}
+					[[fallthrough]];
 				case Teleport:
 				case Teleport_NoFog:
 				case Teleport_Line:

src/scripting/decorate/thingdef_parse.cpp

@@ -1345,6 +1345,7 @@ void ParseDecorate (FScanner &sc, PNamespace *ns)
 				ParseDamageDefinition(sc);
 				break;
 			}
+			[[fallthrough]];
 		default:
 			sc.RestorePos(pos);
 			ParseOldDecoration(sc, DEF_Decoration, ns);

src/scripting/zscript/zcc_compile_doom.cpp

@@ -296,6 +296,7 @@ void ZCCDoomCompiler::DispatchProperty(FPropertyInfo *prop, ZCC_PropertyStmt *pr
 
 			case 'C':	// this parser accepts colors only in string form.
 				pref.i = 1;
+				[[fallthrough]];
 			case 'S':
 			case 'T': // a filtered string (ZScript only parses filtered strings so there's nothing to do here.)
 				conv.s = GetStringConst(ex, ctx);

src/wi_stuff.cpp

@@ -461,6 +461,7 @@ bool DInterBackground::LoadBackground(bool isenterpic)
 					an.LevelName = sc.String;
 					sc.MustGetString();
 					caseval = sc.MustMatchString(WI_Cmd);
+					[[fallthrough]];
 
 				default:
 					switch (caseval)