Use FLEXIBLE_ARRAY_MEMBER in a bunch more places.

Replace some bogus "x[1]" declarations with "x[FLEXIBLE_ARRAY_MEMBER]".
Aside from being more self-documenting, this should help prevent bogus
warnings from static code analyzers and perhaps compiler misoptimizations.

This patch is just a down payment on eliminating the whole problem, but
it gets rid of a lot of easy-to-fix cases.

Note that the main problem with doing this is that one must no longer rely
on computing sizeof(the containing struct), since the result would be
compiler-dependent.  Instead use offsetof(struct, lastfield).  Autoconf
also warns against spelling that offsetof(struct, lastfield[0]).

Michael Paquier, review and additional fixes by me.

src/include/access/gin_private.h

@@ -322,7 +322,7 @@ typedef struct GinOptions
 {
 	int32		vl_len_;		/* varlena header (do not touch directly!) */
 	bool		useFastUpdate;	/* use fast updates? */
-	int			pendingListCleanupSize;	/* maximum size of pending list */
+	int			pendingListCleanupSize; /* maximum size of pending list */
 } GinOptions;
 
 #define GIN_DEFAULT_USE_FASTUPDATE	true
@@ -389,7 +389,7 @@ typedef struct
 {
 	ItemPointerData first;		/* first item in this posting list (unpacked) */
 	uint16		nbytes;			/* number of bytes that follow */
-	unsigned char bytes[1];		/* varbyte encoded items (variable length) */
+	unsigned char bytes[FLEXIBLE_ARRAY_MEMBER]; /* varbyte encoded items */
 } GinPostingList;
 
 #define SizeOfGinPostingList(plist) (offsetof(GinPostingList, bytes) + SHORTALIGN((plist)->nbytes) )

src/include/access/gist_private.h

@@ -47,7 +47,7 @@ typedef struct
 {
 	BlockNumber prev;
 	uint32		freespace;
-	char		tupledata[1];
+	char		tupledata[FLEXIBLE_ARRAY_MEMBER];
 } GISTNodeBufferPage;
 
 #define BUFFER_PAGE_DATA_OFFSET MAXALIGN(offsetof(GISTNodeBufferPage, tupledata))
@@ -131,7 +131,8 @@ typedef struct GISTSearchItem
 		/* we must store parentlsn to detect whether a split occurred */
 		GISTSearchHeapItem heap;	/* heap info, if heap tuple */
 	}			data;
-	double		distances[1];	/* array with numberOfOrderBys entries */
+	double		distances[FLEXIBLE_ARRAY_MEMBER];		/* numberOfOrderBys
+														 * entries */
 } GISTSearchItem;
 
 #define GISTSearchItemIsHeap(item)	((item).blkno == InvalidBlockNumber)
@@ -144,7 +145,7 @@ typedef struct GISTSearchItem
 typedef struct GISTScanOpaqueData
 {
 	GISTSTATE  *giststate;		/* index information, see above */
-	pairingheap *queue;		/* queue of unvisited items */
+	pairingheap *queue;			/* queue of unvisited items */
 	MemoryContext queueCxt;		/* context holding the queue */
 	bool		qual_ok;		/* false if qual can never be satisfied */
 	bool		firstCall;		/* true until first gistgettuple call */

src/include/access/heapam_xlog.h

@@ -132,7 +132,7 @@ typedef struct xl_heap_multi_insert
 {
 	uint8		flags;
 	uint16		ntuples;
-	OffsetNumber offsets[1];
+	OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
 } xl_heap_multi_insert;
 
 #define SizeOfHeapMultiInsert	offsetof(xl_heap_multi_insert, offsets)

src/include/access/spgist_private.h

@@ -426,7 +426,7 @@ typedef struct spgxlogMoveLeafs
 	 * the dead tuple from the source
 	 *----------
 	 */
-	OffsetNumber offsets[1];
+	OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
 } spgxlogMoveLeafs;
 
 #define SizeOfSpgxlogMoveLeafs	offsetof(spgxlogMoveLeafs, offsets)
@@ -534,7 +534,7 @@ typedef struct spgxlogPickSplit
 	 *		list of leaf tuples, length nInsert (unaligned!)
 	 *----------
 	 */
-	OffsetNumber offsets[1];
+	OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
 } spgxlogPickSplit;
 
 #define SizeOfSpgxlogPickSplit offsetof(spgxlogPickSplit, offsets)
@@ -558,7 +558,7 @@ typedef struct spgxlogVacuumLeaf
 	 *		tuple numbers to insert in nextOffset links
 	 *----------
 	 */
-	OffsetNumber offsets[1];
+	OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
 } spgxlogVacuumLeaf;
 
 #define SizeOfSpgxlogVacuumLeaf offsetof(spgxlogVacuumLeaf, offsets)
@@ -571,7 +571,7 @@ typedef struct spgxlogVacuumRoot
 	spgxlogState stateSrc;
 
 	/* offsets of tuples to delete follow */
-	OffsetNumber offsets[1];
+	OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
 } spgxlogVacuumRoot;
 
 #define SizeOfSpgxlogVacuumRoot offsetof(spgxlogVacuumRoot, offsets)
@@ -583,7 +583,7 @@ typedef struct spgxlogVacuumRedirect
 	TransactionId newestRedirectXid;	/* newest XID of removed redirects */
 
 	/* offsets of redirect tuples to make placeholders follow */
-	OffsetNumber offsets[1];
+	OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
 } spgxlogVacuumRedirect;
 
 #define SizeOfSpgxlogVacuumRedirect offsetof(spgxlogVacuumRedirect, offsets)

src/include/access/xact.h

@@ -118,7 +118,7 @@ typedef struct xl_xact_assignment
 {
 	TransactionId xtop;			/* assigned XID's top-level XID */
 	int			nsubxacts;		/* number of subtransaction XIDs */
-	TransactionId xsub[1];		/* assigned subxids */
+	TransactionId xsub[FLEXIBLE_ARRAY_MEMBER];	/* assigned subxids */
 } xl_xact_assignment;
 
 #define MinSizeOfXactAssignment offsetof(xl_xact_assignment, xsub)
@@ -128,7 +128,7 @@ typedef struct xl_xact_commit_compact
 	TimestampTz xact_time;		/* time of commit */
 	int			nsubxacts;		/* number of subtransaction XIDs */
 	/* ARRAY OF COMMITTED SUBTRANSACTION XIDs FOLLOWS */
-	TransactionId subxacts[1];	/* VARIABLE LENGTH ARRAY */
+	TransactionId subxacts[FLEXIBLE_ARRAY_MEMBER];
 } xl_xact_commit_compact;
 
 #define MinSizeOfXactCommitCompact offsetof(xl_xact_commit_compact, subxacts)
@@ -143,7 +143,7 @@ typedef struct xl_xact_commit
 	Oid			dbId;			/* MyDatabaseId */
 	Oid			tsId;			/* MyDatabaseTableSpace */
 	/* Array of RelFileNode(s) to drop at commit */
-	RelFileNode xnodes[1];		/* VARIABLE LENGTH ARRAY */
+	RelFileNode xnodes[FLEXIBLE_ARRAY_MEMBER];
 	/* ARRAY OF COMMITTED SUBTRANSACTION XIDs FOLLOWS */
 	/* ARRAY OF SHARED INVALIDATION MESSAGES FOLLOWS */
 } xl_xact_commit;
@@ -171,7 +171,7 @@ typedef struct xl_xact_abort
 	int			nrels;			/* number of RelFileNodes */
 	int			nsubxacts;		/* number of subtransaction XIDs */
 	/* Array of RelFileNode(s) to drop at abort */
-	RelFileNode xnodes[1];		/* VARIABLE LENGTH ARRAY */
+	RelFileNode xnodes[FLEXIBLE_ARRAY_MEMBER];
 	/* ARRAY OF ABORTED SUBTRANSACTION XIDs FOLLOWS */
 } xl_xact_abort;