Clean up some stuff in new contrib/bloom module.

Coverity complained about implicit sign-extension in the
BloomPageGetFreeSpace macro, probably because sizeOfBloomTuple isn't wide
enough for size calculations.  No overflow is really possible as long as
maxoff and sizeOfBloomTuple are small enough to represent a realistic
situation, but it seems like a good idea to declare sizeOfBloomTuple as
Size not int32.

Add missing check on BloomPageAddItem() result, again from Coverity.

Avoid core dump due to not allocating so->sign array when
scan->numberOfKeys is zero.  Also thanks to Coverity.

Use FLEXIBLE_ARRAY_MEMBER rather than declaring an array as size 1
when it isn't necessarily.

Very minor beautification of related code.

Unfortunately, none of the Coverity-detected mistakes look like they
could account for the remaining buildfarm unhappiness with this
module.  It's barely possible that the FLEXIBLE_ARRAY_MEMBER mistake
does account for that, if it's enabling bogus compiler optimizations;
but I'm not terribly optimistic.  We probably still have bugs to
find here.

contrib/bloom/blinsert.c

@@ -96,10 +96,10 @@ bloomBuildCallback(Relation index, HeapTuple htup, Datum *values,
 
 		initCachedPage(buildstate);
 
-		if (BloomPageAddItem(&buildstate->blstate, buildstate->data, itup) == false)
+		if (!BloomPageAddItem(&buildstate->blstate, buildstate->data, itup))
 		{
 			/* We shouldn't be here since we're inserting to the empty page */
-			elog(ERROR, "can not add new tuple");
+			elog(ERROR, "could not add new bloom tuple to empty page");
 		}
 	}
 
@@ -298,7 +298,12 @@ blinsert(Relation index, Datum *values, bool *isnull,
 	metaData = BloomPageGetMeta(metaPage);
 	page = GenericXLogRegister(state, buffer, true);
 	BloomInitPage(page, 0);
-	BloomPageAddItem(&blstate, page, itup);
+
+	if (!BloomPageAddItem(&blstate, page, itup))
+	{
+		/* We shouldn't be here since we're inserting to the empty page */
+		elog(ERROR, "could not add new bloom tuple to empty page");
+	}
 
 	metaData->nStart = 0;
 	metaData->nEnd = 1;

contrib/bloom/bloom.h

@@ -118,7 +118,7 @@ typedef struct BloomState
 	 * sizeOfBloomTuple is index's specific, and it depends on reloptions, so
 	 * precompute it
 	 */
-	int32		sizeOfBloomTuple;
+	Size		sizeOfBloomTuple;
 }	BloomState;
 
 #define BloomPageGetFreeSpace(state, page) \
@@ -134,7 +134,7 @@ typedef uint16 SignType;
 typedef struct BloomTuple
 {
 	ItemPointerData heapPtr;
-	SignType	sign[1];
+	SignType	sign[FLEXIBLE_ARRAY_MEMBER];
 }	BloomTuple;
 
 #define BLOOMTUPLEHDRSZ offsetof(BloomTuple, sign)

contrib/bloom/blscan.c

@@ -94,7 +94,7 @@ blgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
 	BufferAccessStrategy bas;
 	BloomScanOpaque so = (BloomScanOpaque) scan->opaque;
 
-	if (so->sign == NULL && scan->numberOfKeys > 0)
+	if (so->sign == NULL)
 	{
 		/* New search: have to calculate search signature */
 		ScanKey		skey = scan->keyData;
@@ -151,10 +151,13 @@ blgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
 				bool		res = true;
 
 				/* Check index signature with scan signature */
-				for (i = 0; res && i < so->state.opts->bloomLength; i++)
+				for (i = 0; i < so->state.opts->bloomLength; i++)
 				{
 					if ((itup->sign[i] & so->sign[i]) != so->sign[i])
+					{
 						res = false;
+						break;
+					}
 				}
 
 				/* Add matching tuples to bitmap */