Dial back -Wimplicit-fallthrough to level 3

The additional pain from level 4 is excessive for the gain.

Also revert all the source annotation changes to their original
wordings, to avoid back-patching pain.

Discussion: https://postgr.es/m/31166.1589378554@sss.pgh.pa.us

Author: alvherre

configure

@@ -5553,15 +5553,15 @@ fi
 
 
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wimplicit-fallthrough=4, for CFLAGS" >&5
-$as_echo_n "checking whether ${CC} supports -Wimplicit-fallthrough=4, for CFLAGS... " >&6; }
-if ${pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_4+:} false; then :
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wimplicit-fallthrough=3, for CFLAGS" >&5
+$as_echo_n "checking whether ${CC} supports -Wimplicit-fallthrough=3, for CFLAGS... " >&6; }
+if ${pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_3+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   pgac_save_CFLAGS=$CFLAGS
 pgac_save_CC=$CC
 CC=${CC}
-CFLAGS="${CFLAGS} -Wimplicit-fallthrough=4"
+CFLAGS="${CFLAGS} -Wimplicit-fallthrough=3"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -5576,31 +5576,31 @@ main ()
 }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
-  pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_4=yes
+  pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_3=yes
 else
-  pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_4=no
+  pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_3=no
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 ac_c_werror_flag=$ac_save_c_werror_flag
 CFLAGS="$pgac_save_CFLAGS"
 CC="$pgac_save_CC"
 fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_4" >&5
-$as_echo "$pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_4" >&6; }
-if test x"$pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_4" = x"yes"; then
-  CFLAGS="${CFLAGS} -Wimplicit-fallthrough=4"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_3" >&5
+$as_echo "$pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_3" >&6; }
+if test x"$pgac_cv_prog_CC_cflags__Wimplicit_fallthrough_3" = x"yes"; then
+  CFLAGS="${CFLAGS} -Wimplicit-fallthrough=3"
 fi
 
 
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CXX} supports -Wimplicit-fallthrough=4, for CXXFLAGS" >&5
-$as_echo_n "checking whether ${CXX} supports -Wimplicit-fallthrough=4, for CXXFLAGS... " >&6; }
-if ${pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_4+:} false; then :
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CXX} supports -Wimplicit-fallthrough=3, for CXXFLAGS" >&5
+$as_echo_n "checking whether ${CXX} supports -Wimplicit-fallthrough=3, for CXXFLAGS... " >&6; }
+if ${pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_3+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   pgac_save_CXXFLAGS=$CXXFLAGS
 pgac_save_CXX=$CXX
 CXX=${CXX}
-CXXFLAGS="${CXXFLAGS} -Wimplicit-fallthrough=4"
+CXXFLAGS="${CXXFLAGS} -Wimplicit-fallthrough=3"
 ac_save_cxx_werror_flag=$ac_cxx_werror_flag
 ac_cxx_werror_flag=yes
 ac_ext=cpp
@@ -5621,9 +5621,9 @@ main ()
 }
 _ACEOF
 if ac_fn_cxx_try_compile "$LINENO"; then :
-  pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_4=yes
+  pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_3=yes
 else
-  pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_4=no
+  pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_3=no
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 ac_ext=c
@@ -5636,10 +5636,10 @@ ac_cxx_werror_flag=$ac_save_cxx_werror_flag
 CXXFLAGS="$pgac_save_CXXFLAGS"
 CXX="$pgac_save_CXX"
 fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_4" >&5
-$as_echo "$pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_4" >&6; }
-if test x"$pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_4" = x"yes"; then
-  CXXFLAGS="${CXXFLAGS} -Wimplicit-fallthrough=4"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_3" >&5
+$as_echo "$pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_3" >&6; }
+if test x"$pgac_cv_prog_CXX_cxxflags__Wimplicit_fallthrough_3" = x"yes"; then
+  CXXFLAGS="${CXXFLAGS} -Wimplicit-fallthrough=3"
 fi
 
 

configure.in

@@ -496,8 +496,8 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CXX_CFLAGS_OPT([-Wendif-labels])
   PGAC_PROG_CC_CFLAGS_OPT([-Wmissing-format-attribute])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wmissing-format-attribute])
-  PGAC_PROG_CC_CFLAGS_OPT([-Wimplicit-fallthrough=4])
-  PGAC_PROG_CXX_CFLAGS_OPT([-Wimplicit-fallthrough=4])
+  PGAC_PROG_CC_CFLAGS_OPT([-Wimplicit-fallthrough=3])
+  PGAC_PROG_CXX_CFLAGS_OPT([-Wimplicit-fallthrough=3])
   # This was included in -Wall/-Wformat in older GCC versions
   PGAC_PROG_CC_CFLAGS_OPT([-Wformat-security])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wformat-security])

contrib/pgcrypto/pgp-info.c

@@ -169,7 +169,7 @@ pgp_get_keyid(MBuf *pgp_data, char *dst)
 				break;
 			case PGP_PKT_SYMENCRYPTED_SESSKEY:
 				got_symenc_key++;
-				/* FALLTHROUGH */
+				/* fall through */
 			case PGP_PKT_SIGNATURE:
 			case PGP_PKT_MARKER:
 			case PGP_PKT_TRUST:

src/backend/access/heap/heapam_handler.c

@@ -814,7 +814,7 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
 				break;
 			case HEAPTUPLE_RECENTLY_DEAD:
 				*tups_recently_dead += 1;
-				/* FALLTHROUGH */
+				/* fall through */
 			case HEAPTUPLE_LIVE:
 				/* Live or recently dead, must copy it */
 				isdead = false;

src/backend/catalog/dependency.c

@@ -615,7 +615,7 @@ findDependentObjects(const ObjectAddress *object,
 					break;
 
 				/* Otherwise, treat this like an internal dependency */
-				/* FALLTHROUGH */
+				/* FALL THRU */
 
 			case DEPENDENCY_INTERNAL:
 

src/backend/commands/tablecmds.c

@@ -12467,7 +12467,7 @@ ATExecChangeOwner(Oid relationOid, Oid newOwnerId, bool recursing, LOCKMODE lock
 		case RELKIND_TOASTVALUE:
 			if (recursing)
 				break;
-			/* FALLTHROUGH */
+			/* FALL THRU */
 		default:
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),

src/backend/commands/trigger.c

@@ -3877,7 +3877,7 @@ AfterTriggerExecute(EState *estate,
 											 trig_tuple_slot2))
 					elog(ERROR, "failed to fetch tuple2 for AFTER trigger");
 			}
-			/* FALLTHROUGH */
+			/* fall through */
 		case AFTER_TRIGGER_FDW_REUSE:
 
 			/*

src/backend/executor/nodeHash.c

@@ -256,7 +256,7 @@ MultiExecParallelHash(HashState *node)
 			 * way, wait for everyone to arrive here so we can proceed.
 			 */
 			BarrierArriveAndWait(build_barrier, WAIT_EVENT_HASH_BUILD_ALLOCATING);
-			/* FALLTHROUGH */
+			/* Fall through. */
 
 		case PHJ_BUILD_HASHING_INNER:
 
@@ -1181,13 +1181,13 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable)
 				/* All other participants just flush their tuples to disk. */
 				ExecParallelHashCloseBatchAccessors(hashtable);
 			}
-			/* FALLTHROUGH */
+			/* Fall through. */
 
 		case PHJ_GROW_BATCHES_ALLOCATING:
 			/* Wait for the above to be finished. */
 			BarrierArriveAndWait(&pstate->grow_batches_barrier,
 								 WAIT_EVENT_HASH_GROW_BATCHES_ALLOCATING);
-			/* FALLTHROUGH */
+			/* Fall through. */
 
 		case PHJ_GROW_BATCHES_REPARTITIONING:
 			/* Make sure that we have the current dimensions and buckets. */
@@ -1200,7 +1200,7 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable)
 			/* Wait for the above to be finished. */
 			BarrierArriveAndWait(&pstate->grow_batches_barrier,
 								 WAIT_EVENT_HASH_GROW_BATCHES_REPARTITIONING);
-			/* FALLTHROUGH */
+			/* Fall through. */
 
 		case PHJ_GROW_BATCHES_DECIDING:
 
@@ -1255,7 +1255,7 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable)
 				dsa_free(hashtable->area, pstate->old_batches);
 				pstate->old_batches = InvalidDsaPointer;
 			}
-			/* FALLTHROUGH */
+			/* Fall through. */
 
 		case PHJ_GROW_BATCHES_FINISHING:
 			/* Wait for the above to complete. */
@@ -1533,13 +1533,13 @@ ExecParallelHashIncreaseNumBuckets(HashJoinTable hashtable)
 				/* Clear the flag. */
 				pstate->growth = PHJ_GROWTH_OK;
 			}
-			/* FALLTHROUGH */
+			/* Fall through. */
 
 		case PHJ_GROW_BUCKETS_ALLOCATING:
 			/* Wait for the above to complete. */
 			BarrierArriveAndWait(&pstate->grow_buckets_barrier,
 								 WAIT_EVENT_HASH_GROW_BUCKETS_ALLOCATING);
-			/* FALLTHROUGH */
+			/* Fall through. */
 
 		case PHJ_GROW_BUCKETS_REINSERTING:
 			/* Reinsert all tuples into the hash table. */

src/backend/executor/nodeHashjoin.c

@@ -340,7 +340,7 @@ ExecHashJoinImpl(PlanState *pstate, bool parallel)
 				else
 					node->hj_JoinState = HJ_NEED_NEW_OUTER;
 
-				/* FALLTHROUGH */
+				/* FALL THRU */
 
 			case HJ_NEED_NEW_OUTER:
 
@@ -413,7 +413,7 @@ ExecHashJoinImpl(PlanState *pstate, bool parallel)
 				/* OK, let's scan the bucket for matches */
 				node->hj_JoinState = HJ_SCAN_BUCKET;
 
-				/* FALLTHROUGH */
+				/* FALL THRU */
 
 			case HJ_SCAN_BUCKET:
 
@@ -1137,13 +1137,13 @@ ExecParallelHashJoinNewBatch(HashJoinState *hjstate)
 					if (BarrierArriveAndWait(batch_barrier,
 											 WAIT_EVENT_HASH_BATCH_ELECTING))
 						ExecParallelHashTableAlloc(hashtable, batchno);
-					/* FALLTHROUGH */
+					/* Fall through. */
 
 				case PHJ_BATCH_ALLOCATING:
 					/* Wait for allocation to complete. */
 					BarrierArriveAndWait(batch_barrier,
 										 WAIT_EVENT_HASH_BATCH_ALLOCATING);
-					/* FALLTHROUGH */
+					/* Fall through. */
 
 				case PHJ_BATCH_LOADING:
 					/* Start (or join in) loading tuples. */
@@ -1163,7 +1163,7 @@ ExecParallelHashJoinNewBatch(HashJoinState *hjstate)
 					sts_end_parallel_scan(inner_tuples);
 					BarrierArriveAndWait(batch_barrier,
 										 WAIT_EVENT_HASH_BATCH_LOADING);
-					/* FALLTHROUGH */
+					/* Fall through. */
 
 				case PHJ_BATCH_PROBING:
 

src/backend/executor/nodeLimit.c

@@ -69,7 +69,7 @@ ExecLimit(PlanState *pstate)
 			 */
 			recompute_limits(node);
 
-			/* FALLTHROUGH */
+			/* FALL THRU */
 
 		case LIMIT_RESCAN:
 
@@ -216,7 +216,7 @@ ExecLimit(PlanState *pstate)
 			}
 
 			Assert(node->lstate == LIMIT_WINDOWEND_TIES);
-			/* FALLTHROUGH */
+			/* FALL THRU */
 
 		case LIMIT_WINDOWEND_TIES:
 			if (ScanDirectionIsForward(direction))