Add -Wimplicit-fallthrough to CFLAGS and CXXFLAGS

Use it at level 4, a bit more restrictive than the default level, and
tweak our commanding comments to FALLTHROUGH.

(However, leave zic.c alone, since it's external code; to avoid the
warnings that would appear there, change CFLAGS for that file in the
Makefile.)

Author: Julien Rouhaud <[email protected]>
Author: Álvaro Herrera <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Discussion: https://postgr.es/m/20200412081825.qyo5vwwco3fv4gdo@nol
Discussion: https://postgr.es/m/flat/[email protected]

4 files changed, 30 insertions, 30 deletions

diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index aab5802edb4..657b8f03766 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -3425,7 +3425,7 @@ DCH_from_char(FormatNode *node, const char *in, TmFromChar *out,
 			case DCH_FF5:
 			case DCH_FF6:
 				out->ff = n->key->id - DCH_FF1 + 1;
-				/* fall through */
+				/* FALLTHROUGH */
 			case DCH_US:		/* microsecond */
 				len = from_char_parse_int_len(&out->us, &s,
 											  n->key->id == DCH_US ? 6 :
diff --git a/src/backend/utils/adt/jsonb_util.c b/src/backend/utils/adt/jsonb_util.c
index 04b70c805b4..52ec80af045 100644
--- a/src/backend/utils/adt/jsonb_util.c
+++ b/src/backend/utils/adt/jsonb_util.c
@@ -637,7 +637,7 @@ pushJsonbValueScalar(JsonbParseState **pstate, JsonbIteratorToken seq,
 			break;
 		case WJB_END_OBJECT:
 			uniqueifyJsonbObject(&(*pstate)->contVal);
-			/* fall through! */
+			/* FALLTHROUGH */
 		case WJB_END_ARRAY:
 			/* Steps here common to WJB_END_OBJECT case */
 			Assert(!scalarVal);
diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index 4caffb58040..d28d3c1628b 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -3866,14 +3866,14 @@ timestamp_trunc(PG_FUNCTION_ARGS)
 					tm->tm_year = ((tm->tm_year + 999) / 1000) * 1000 - 999;
 				else
 					tm->tm_year = -((999 - (tm->tm_year - 1)) / 1000) * 1000 + 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_CENTURY:
 				/* see comments in timestamptz_trunc */
 				if (tm->tm_year > 0)
 					tm->tm_year = ((tm->tm_year + 99) / 100) * 100 - 99;
 				else
 					tm->tm_year = -((99 - (tm->tm_year - 1)) / 100) * 100 + 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_DECADE:
 				/* see comments in timestamptz_trunc */
 				if (val != DTK_MILLENNIUM && val != DTK_CENTURY)
@@ -3883,25 +3883,25 @@ timestamp_trunc(PG_FUNCTION_ARGS)
 					else
 						tm->tm_year = -((8 - (tm->tm_year - 1)) / 10) * 10;
 				}
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_YEAR:
 				tm->tm_mon = 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_QUARTER:
 				tm->tm_mon = (3 * ((tm->tm_mon - 1) / 3)) + 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_MONTH:
 				tm->tm_mday = 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_DAY:
 				tm->tm_hour = 0;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_HOUR:
 				tm->tm_min = 0;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_MINUTE:
 				tm->tm_sec = 0;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_SECOND:
 				fsec = 0;
 				break;
@@ -4007,14 +4007,14 @@ timestamptz_trunc_internal(text *units, TimestampTz timestamp, pg_tz *tzp)
 					tm->tm_year = ((tm->tm_year + 999) / 1000) * 1000 - 999;
 				else
 					tm->tm_year = -((999 - (tm->tm_year - 1)) / 1000) * 1000 + 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_CENTURY:
 				/* truncating to the century? as above: -100, 1, 101... */
 				if (tm->tm_year > 0)
 					tm->tm_year = ((tm->tm_year + 99) / 100) * 100 - 99;
 				else
 					tm->tm_year = -((99 - (tm->tm_year - 1)) / 100) * 100 + 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_DECADE:
 
 				/*
@@ -4028,26 +4028,26 @@ timestamptz_trunc_internal(text *units, TimestampTz timestamp, pg_tz *tzp)
 					else
 						tm->tm_year = -((8 - (tm->tm_year - 1)) / 10) * 10;
 				}
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_YEAR:
 				tm->tm_mon = 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_QUARTER:
 				tm->tm_mon = (3 * ((tm->tm_mon - 1) / 3)) + 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_MONTH:
 				tm->tm_mday = 1;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_DAY:
 				tm->tm_hour = 0;
 				redotz = true;	/* for all cases >= DAY */
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_HOUR:
 				tm->tm_min = 0;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_MINUTE:
 				tm->tm_sec = 0;
-				/* FALL THRU */
+				/* FALLTHROUGH */
 			case DTK_SECOND:
 				fsec = 0;
 				break;
@@ -4195,33 +4195,33 @@ interval_trunc(PG_FUNCTION_ARGS)
 				case DTK_MILLENNIUM:
 					/* caution: C division may have negative remainder */
 					tm->tm_year = (tm->tm_year / 1000) * 1000;
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_CENTURY:
 					/* caution: C division may have negative remainder */
 					tm->tm_year = (tm->tm_year / 100) * 100;
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_DECADE:
 					/* caution: C division may have negative remainder */
 					tm->tm_year = (tm->tm_year / 10) * 10;
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_YEAR:
 					tm->tm_mon = 0;
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_QUARTER:
 					tm->tm_mon = 3 * (tm->tm_mon / 3);
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_MONTH:
 					tm->tm_mday = 0;
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_DAY:
 					tm->tm_hour = 0;
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_HOUR:
 					tm->tm_min = 0;
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_MINUTE:
 					tm->tm_sec = 0;
-					/* FALL THRU */
+					/* FALLTHROUGH */
 				case DTK_SECOND:
 					fsec = 0;
 					break;
diff --git a/src/backend/utils/adt/tsginidx.c b/src/backend/utils/adt/tsginidx.c
index 2d656168fca..a6d7b9805ad 100644
--- a/src/backend/utils/adt/tsginidx.c
+++ b/src/backend/utils/adt/tsginidx.c
@@ -264,7 +264,7 @@ TS_execute_ternary(GinChkVal *gcv, QueryItem *curitem, bool in_phrase)
 			/* Pass down in_phrase == true in case there's a NOT below */
 			in_phrase = true;
 
-			/* FALL THRU */
+			/* FALLTHROUGH */
 
 		case OP_AND:
 			val1 = TS_execute_ternary(gcv, curitem + curitem->qoperator.left,