Static assertions cleanup

Because we added StaticAssertStmt() first before StaticAssertDecl(),
some uses as well as the instructions in c.h are now a bit backwards
from the "native" way static assertions are meant to be used in C.
This updates the guidance and moves some static assertions to better
places.

Specifically, since the addition of StaticAssertDecl(), we can put
static assertions at the file level.  This moves a number of static
assertions out of function bodies, where they might have been stuck
out of necessity, to perhaps better places at the file level or in
header files.

Also, when the static assertion appears in a position where a
declaration is allowed, then using StaticAssertDecl() is more native
than StaticAssertStmt().

Reviewed-by: John Naylor <john.naylor@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/941a04e7-dd6f-c0e4-8cdf-a33b3338cbda%40enterprisedb.com

src/backend/access/heap/heapam.c

@@ -5783,10 +5783,6 @@ heap_finish_speculative(Relation relation, ItemPointer tid)
 
 	htup = (HeapTupleHeader) PageGetItem(page, lp);
 
-	/* SpecTokenOffsetNumber should be distinguishable from any real offset */
-	StaticAssertStmt(MaxOffsetNumber < SpecTokenOffsetNumber,
-					 "invalid speculative token constant");
-
 	/* NO EREPORT(ERROR) from here till changes are logged */
 	START_CRIT_SECTION();
 
@@ -7921,7 +7917,7 @@ index_delete_sort(TM_IndexDeleteOp *delstate)
 	const int	gaps[9] = {1968, 861, 336, 112, 48, 21, 7, 3, 1};
 
 	/* Think carefully before changing anything here -- keep swaps cheap */
-	StaticAssertStmt(sizeof(TM_IndexDelete) <= 8,
+	StaticAssertDecl(sizeof(TM_IndexDelete) <= 8,
 					 "element size exceeds 8 bytes");
 
 	for (int g = 0; g < lengthof(gaps); g++)

src/backend/access/nbtree/nbtutils.c

@@ -2486,13 +2486,6 @@ _bt_check_natts(Relation rel, bool heapkeyspace, Page page, OffsetNumber offnum)
 	Assert(offnum >= FirstOffsetNumber &&
 		   offnum <= PageGetMaxOffsetNumber(page));
 
-	/*
-	 * Mask allocated for number of keys in index tuple must be able to fit
-	 * maximum possible number of index attributes
-	 */
-	StaticAssertStmt(BT_OFFSET_MASK >= INDEX_MAX_KEYS,
-					 "BT_OFFSET_MASK can't fit INDEX_MAX_KEYS");
-
 	itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, offnum));
 	tupnatts = BTreeTupleGetNAtts(itup, rel);
 

src/backend/access/transam/clog.c

@@ -275,7 +275,7 @@ TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
 						   bool all_xact_same_page)
 {
 	/* Can't use group update when PGPROC overflows. */
-	StaticAssertStmt(THRESHOLD_SUBTRANS_CLOG_OPT <= PGPROC_MAX_CACHED_SUBXIDS,
+	StaticAssertDecl(THRESHOLD_SUBTRANS_CLOG_OPT <= PGPROC_MAX_CACHED_SUBXIDS,
 					 "group clog threshold less than PGPROC cached subxids");
 
 	/*

src/backend/access/transam/xlog.c

@@ -3883,15 +3883,6 @@ WriteControlFile(void)
 	int			fd;
 	char		buffer[PG_CONTROL_FILE_SIZE];	/* need not be aligned */
 
-	/*
-	 * Ensure that the size of the pg_control data structure is sane.  See the
-	 * comments for these symbols in pg_control.h.
-	 */
-	StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_MAX_SAFE_SIZE,
-					 "pg_control is too large for atomic disk writes");
-	StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_FILE_SIZE,
-					 "sizeof(ControlFileData) exceeds PG_CONTROL_FILE_SIZE");
-
 	/*
 	 * Initialize version and compatibility-check fields
 	 */

src/backend/backup/basebackup.c

@@ -370,7 +370,7 @@ perform_base_backup(basebackup_options *opt, bbsink *sink)
 			else
 			{
 				/* Properly terminate the tarfile. */
-				StaticAssertStmt(2 * TAR_BLOCK_SIZE <= BLCKSZ,
+				StaticAssertDecl(2 * TAR_BLOCK_SIZE <= BLCKSZ,
 								 "BLCKSZ too small for 2 tar blocks");
 				memset(sink->bbs_buffer, 0, 2 * TAR_BLOCK_SIZE);
 				bbsink_archive_contents(sink, 2 * TAR_BLOCK_SIZE);
@@ -1745,7 +1745,7 @@ _tarWriteHeader(bbsink *sink, const char *filename, const char *linktarget,
 		 * large enough to fit an entire tar block. We double-check by means
 		 * of these assertions.
 		 */
-		StaticAssertStmt(TAR_BLOCK_SIZE <= BLCKSZ,
+		StaticAssertDecl(TAR_BLOCK_SIZE <= BLCKSZ,
 						 "BLCKSZ too small for tar block");
 		Assert(sink->bbs_buffer_length >= TAR_BLOCK_SIZE);
 

src/backend/catalog/dependency.c

@@ -191,6 +191,12 @@ static const Oid object_classes[] = {
 	TransformRelationId			/* OCLASS_TRANSFORM */
 };
 
+/*
+ * Make sure object_classes is kept up to date with the ObjectClass enum.
+ */
+StaticAssertDecl(lengthof(object_classes) == LAST_OCLASS + 1,
+				 "object_classes[] must cover all ObjectClasses");
+
 
 static void findDependentObjects(const ObjectAddress *object,
 								 int objflags,
@@ -2550,12 +2556,6 @@ add_object_address(ObjectClass oclass, Oid objectId, int32 subId,
 {
 	ObjectAddress *item;
 
-	/*
-	 * Make sure object_classes is kept up to date with the ObjectClass enum.
-	 */
-	StaticAssertStmt(lengthof(object_classes) == LAST_OCLASS + 1,
-					 "object_classes[] must cover all ObjectClasses");
-
 	/* enlarge array if needed */
 	if (addrs->numrefs >= addrs->maxrefs)
 	{

src/backend/executor/execExprInterp.c

@@ -496,7 +496,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 		&&CASE_EEOP_LAST
 	};
 
-	StaticAssertStmt(lengthof(dispatch_table) == EEOP_LAST + 1,
+	StaticAssertDecl(lengthof(dispatch_table) == EEOP_LAST + 1,
 					 "dispatch_table out of whack with ExprEvalOp");
 
 	if (unlikely(state == NULL))

src/backend/libpq/auth-scram.c

@@ -1443,7 +1443,7 @@ scram_mock_salt(const char *username)
 	 * not larger than the SHA256 digest length.  If the salt is smaller, the
 	 * caller will just ignore the extra data.)
 	 */
-	StaticAssertStmt(PG_SHA256_DIGEST_LENGTH >= SCRAM_DEFAULT_SALT_LEN,
+	StaticAssertDecl(PG_SHA256_DIGEST_LENGTH >= SCRAM_DEFAULT_SALT_LEN,
 					 "salt length greater than SHA256 digest length");
 
 	ctx = pg_cryptohash_create(PG_SHA256);

src/backend/libpq/hba.c

@@ -127,6 +127,12 @@ static const char *const UserAuthName[] =
 	"peer"
 };
 
+/*
+ * Make sure UserAuthName[] tracks additions to the UserAuth enum
+ */
+StaticAssertDecl(lengthof(UserAuthName) == USER_AUTH_LAST + 1,
+				 "UserAuthName[] must match the UserAuth enum");
+
 
 static List *tokenize_expand_file(List *tokens, const char *outer_filename,
 								  const char *inc_filename, int elevel,
@@ -3117,11 +3123,5 @@ hba_getauthmethod(hbaPort *port)
 const char *
 hba_authname(UserAuth auth_method)
 {
-	/*
-	 * Make sure UserAuthName[] tracks additions to the UserAuth enum
-	 */
-	StaticAssertStmt(lengthof(UserAuthName) == USER_AUTH_LAST + 1,
-					 "UserAuthName[] must match the UserAuth enum");
-
 	return UserAuthName[auth_method];
 }

src/backend/port/atomics.c

@@ -54,7 +54,7 @@ pg_extern_compiler_barrier(void)
 void
 pg_atomic_init_flag_impl(volatile pg_atomic_flag *ptr)
 {
-	StaticAssertStmt(sizeof(ptr->sema) >= sizeof(slock_t),
+	StaticAssertDecl(sizeof(ptr->sema) >= sizeof(slock_t),
 					 "size mismatch of atomic_flag vs slock_t");
 
 #ifndef HAVE_SPINLOCKS
@@ -105,7 +105,7 @@ pg_atomic_unlocked_test_flag_impl(volatile pg_atomic_flag *ptr)
 void
 pg_atomic_init_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val_)
 {
-	StaticAssertStmt(sizeof(ptr->sema) >= sizeof(slock_t),
+	StaticAssertDecl(sizeof(ptr->sema) >= sizeof(slock_t),
 					 "size mismatch of atomic_uint32 vs slock_t");
 
 	/*
@@ -181,7 +181,7 @@ pg_atomic_fetch_add_u32_impl(volatile pg_atomic_uint32 *ptr, int32 add_)
 void
 pg_atomic_init_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val_)
 {
-	StaticAssertStmt(sizeof(ptr->sema) >= sizeof(slock_t),
+	StaticAssertDecl(sizeof(ptr->sema) >= sizeof(slock_t),
 					 "size mismatch of atomic_uint64 vs slock_t");
 
 	/*

src/backend/storage/lmgr/lwlock.c

@@ -108,6 +108,9 @@ extern slock_t *ShmemLock;
 /* Must be greater than MAX_BACKENDS - which is 2^23-1, so we're fine. */
 #define LW_SHARED_MASK				((uint32) ((1 << 24)-1))
 
+StaticAssertDecl(LW_VAL_EXCLUSIVE > (uint32) MAX_BACKENDS,
+				 "MAX_BACKENDS too big for lwlock.c");
+
 /*
  * There are three sorts of LWLock "tranches":
  *
@@ -466,12 +469,6 @@ LWLockShmemSize(void)
 void
 CreateLWLocks(void)
 {
-	StaticAssertStmt(LW_VAL_EXCLUSIVE > (uint32) MAX_BACKENDS,
-					 "MAX_BACKENDS too big for lwlock.c");
-
-	StaticAssertStmt(sizeof(LWLock) <= LWLOCK_PADDED_SIZE,
-					 "Miscalculated LWLock padding");
-
 	if (!IsUnderPostmaster)
 	{
 		Size		spaceLocks = LWLockShmemSize();

src/backend/storage/page/itemptr.c

@@ -17,6 +17,12 @@
 #include "storage/itemptr.h"
 
 
+/*
+ * We really want ItemPointerData to be exactly 6 bytes.
+ */
+StaticAssertDecl(sizeof(ItemPointerData) == 3 * sizeof(uint16),
+				 "ItemPointerData struct is improperly padded");
+
 /*
  * ItemPointerEquals
  *	Returns true if both item pointers point to the same item,
@@ -28,13 +34,6 @@
 bool
 ItemPointerEquals(ItemPointer pointer1, ItemPointer pointer2)
 {
-	/*
-	 * We really want ItemPointerData to be exactly 6 bytes.  This is rather a
-	 * random place to check, but there is no better place.
-	 */
-	StaticAssertStmt(sizeof(ItemPointerData) == 3 * sizeof(uint16),
-					 "ItemPointerData struct is improperly padded");
-
 	if (ItemPointerGetBlockNumber(pointer1) ==
 		ItemPointerGetBlockNumber(pointer2) &&
 		ItemPointerGetOffsetNumber(pointer1) ==

src/backend/utils/adt/numeric.c

@@ -4187,7 +4187,8 @@ int64_div_fast_to_numeric(int64 val1, int log10val2)
 	{
 		static int	pow10[] = {1, 10, 100, 1000};
 
-		StaticAssertStmt(lengthof(pow10) == DEC_DIGITS, "mismatch with DEC_DIGITS");
+		StaticAssertDecl(lengthof(pow10) == DEC_DIGITS, "mismatch with DEC_DIGITS");
+
 		if (unlikely(pg_mul_s64_overflow(val1, pow10[DEC_DIGITS - m], &val1)))
 		{
 			/*

src/backend/utils/adt/tsginidx.c

@@ -236,8 +236,6 @@ gin_tsquery_consistent(PG_FUNCTION_ARGS)
 		 * query.
 		 */
 		gcv.first_item = GETQUERY(query);
-		StaticAssertStmt(sizeof(GinTernaryValue) == sizeof(bool),
-						 "sizes of GinTernaryValue and bool are not equal");
 		gcv.check = (GinTernaryValue *) check;
 		gcv.map_item_operand = (int *) (extra_data[0]);
 

src/backend/utils/adt/xid8funcs.c

@@ -74,6 +74,14 @@ typedef struct
 #define PG_SNAPSHOT_MAX_NXIP \
 	((MaxAllocSize - offsetof(pg_snapshot, xip)) / sizeof(FullTransactionId))
 
+/*
+ * Compile-time limits on the procarray (MAX_BACKENDS processes plus
+ * MAX_BACKENDS prepared transactions) guarantee nxip won't be too large.
+ */
+StaticAssertDecl(MAX_BACKENDS * 2 <= PG_SNAPSHOT_MAX_NXIP,
+				 "possible overflow in pg_current_snapshot()");
+
+
 /*
  * Helper to get a TransactionId from a 64-bit xid with wraparound detection.
  *
@@ -402,13 +410,6 @@ pg_current_snapshot(PG_FUNCTION_ARGS)
 	if (cur == NULL)
 		elog(ERROR, "no active snapshot set");
 
-	/*
-	 * Compile-time limits on the procarray (MAX_BACKENDS processes plus
-	 * MAX_BACKENDS prepared transactions) guarantee nxip won't be too large.
-	 */
-	StaticAssertStmt(MAX_BACKENDS * 2 <= PG_SNAPSHOT_MAX_NXIP,
-					 "possible overflow in pg_current_snapshot()");
-
 	/* allocate */
 	nxip = cur->xcnt;
 	snap = palloc(PG_SNAPSHOT_SIZE(nxip));

src/backend/utils/cache/syscache.c

@@ -1040,6 +1040,9 @@ static const struct cachedesc cacheinfo[] = {
 	}
 };
 
+StaticAssertDecl(lengthof(cacheinfo) == SysCacheSize,
+				 "SysCacheSize does not match syscache.c's array");
+
 static CatCache *SysCache[SysCacheSize];
 
 static bool CacheInitialized = false;
@@ -1068,9 +1071,6 @@ InitCatalogCache(void)
 {
 	int			cacheId;
 
-	StaticAssertStmt(lengthof(cacheinfo) == SysCacheSize,
-					 "SysCacheSize does not match syscache.c's array");
-
 	Assert(!CacheInitialized);
 
 	SysCacheRelationOidSize = SysCacheSupportingRelOidSize = 0;

src/backend/utils/mmgr/aset.c

@@ -306,7 +306,7 @@ AllocSetFreeIndex(Size size)
 					tsize;
 
 		/* Statically assert that we only have a 16-bit input value. */
-		StaticAssertStmt(ALLOC_CHUNK_LIMIT < (1 << 16),
+		StaticAssertDecl(ALLOC_CHUNK_LIMIT < (1 << 16),
 						 "ALLOC_CHUNK_LIMIT must be less than 64kB");
 
 		tsize = size - 1;
@@ -358,10 +358,10 @@ AllocSetContextCreateInternal(MemoryContext parent,
 	AllocBlock	block;
 
 	/* ensure MemoryChunk's size is properly maxaligned */
-	StaticAssertStmt(ALLOC_CHUNKHDRSZ == MAXALIGN(ALLOC_CHUNKHDRSZ),
+	StaticAssertDecl(ALLOC_CHUNKHDRSZ == MAXALIGN(ALLOC_CHUNKHDRSZ),
 					 "sizeof(MemoryChunk) is not maxaligned");
 	/* check we have enough space to store the freelist link */
-	StaticAssertStmt(sizeof(AllocFreeListLink) <= (1 << ALLOC_MINBITS),
+	StaticAssertDecl(sizeof(AllocFreeListLink) <= (1 << ALLOC_MINBITS),
 					 "sizeof(AllocFreeListLink) larger than minimum allocation size");
 
 	/*

src/backend/utils/mmgr/generation.c

@@ -167,7 +167,7 @@ GenerationContextCreate(MemoryContext parent,
 	GenerationBlock *block;
 
 	/* ensure MemoryChunk's size is properly maxaligned */
-	StaticAssertStmt(Generation_CHUNKHDRSZ == MAXALIGN(Generation_CHUNKHDRSZ),
+	StaticAssertDecl(Generation_CHUNKHDRSZ == MAXALIGN(Generation_CHUNKHDRSZ),
 					 "sizeof(MemoryChunk) is not maxaligned");
 
 	/*

src/backend/utils/mmgr/slab.c

@@ -151,7 +151,7 @@ SlabContextCreate(MemoryContext parent,
 	int			i;
 
 	/* ensure MemoryChunk's size is properly maxaligned */
-	StaticAssertStmt(Slab_CHUNKHDRSZ == MAXALIGN(Slab_CHUNKHDRSZ),
+	StaticAssertDecl(Slab_CHUNKHDRSZ == MAXALIGN(Slab_CHUNKHDRSZ),
 					 "sizeof(MemoryChunk) is not maxaligned");
 	Assert(MAXALIGN(chunkSize) <= MEMORYCHUNK_MAX_VALUE);
 

src/common/checksum_helper.c

@@ -177,15 +177,15 @@ pg_checksum_final(pg_checksum_context *context, uint8 *output)
 {
 	int			retval = 0;
 
-	StaticAssertStmt(sizeof(pg_crc32c) <= PG_CHECKSUM_MAX_LENGTH,
+	StaticAssertDecl(sizeof(pg_crc32c) <= PG_CHECKSUM_MAX_LENGTH,
 					 "CRC-32C digest too big for PG_CHECKSUM_MAX_LENGTH");
-	StaticAssertStmt(PG_SHA224_DIGEST_LENGTH <= PG_CHECKSUM_MAX_LENGTH,
+	StaticAssertDecl(PG_SHA224_DIGEST_LENGTH <= PG_CHECKSUM_MAX_LENGTH,
 					 "SHA224 digest too big for PG_CHECKSUM_MAX_LENGTH");
-	StaticAssertStmt(PG_SHA256_DIGEST_LENGTH <= PG_CHECKSUM_MAX_LENGTH,
+	StaticAssertDecl(PG_SHA256_DIGEST_LENGTH <= PG_CHECKSUM_MAX_LENGTH,
 					 "SHA256 digest too big for PG_CHECKSUM_MAX_LENGTH");
-	StaticAssertStmt(PG_SHA384_DIGEST_LENGTH <= PG_CHECKSUM_MAX_LENGTH,
+	StaticAssertDecl(PG_SHA384_DIGEST_LENGTH <= PG_CHECKSUM_MAX_LENGTH,
 					 "SHA384 digest too big for PG_CHECKSUM_MAX_LENGTH");
-	StaticAssertStmt(PG_SHA512_DIGEST_LENGTH <= PG_CHECKSUM_MAX_LENGTH,
+	StaticAssertDecl(PG_SHA512_DIGEST_LENGTH <= PG_CHECKSUM_MAX_LENGTH,
 					 "SHA512 digest too big for PG_CHECKSUM_MAX_LENGTH");
 
 	switch (context->type)

src/common/controldata_utils.c

@@ -149,14 +149,6 @@ update_controlfile(const char *DataDir,
 	char		buffer[PG_CONTROL_FILE_SIZE];
 	char		ControlFilePath[MAXPGPATH];
 
-	/*
-	 * Apply the same static assertions as in backend's WriteControlFile().
-	 */
-	StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_MAX_SAFE_SIZE,
-					 "pg_control is too large for atomic disk writes");
-	StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_FILE_SIZE,
-					 "sizeof(ControlFileData) exceeds PG_CONTROL_FILE_SIZE");
-
 	/* Update timestamp  */
 	ControlFile->time = (pg_time_t) time(NULL);
 

src/common/encnames.c

@@ -451,6 +451,9 @@ static const char *const pg_enc2icu_tbl[] =
 	"KOI8-U",					/* PG_KOI8U */
 };
 
+StaticAssertDecl(lengthof(pg_enc2icu_tbl) == PG_ENCODING_BE_LAST + 1,
+				 "pg_enc2icu_tbl incomplete");
+
 
 /*
  * Is this encoding supported by ICU?
@@ -469,9 +472,6 @@ is_encoding_supported_by_icu(int encoding)
 const char *
 get_encoding_name_for_icu(int encoding)
 {
-	StaticAssertStmt(lengthof(pg_enc2icu_tbl) == PG_ENCODING_BE_LAST + 1,
-					 "pg_enc2icu_tbl incomplete");
-
 	if (!PG_VALID_BE_ENCODING(encoding))
 		return NULL;
 	return pg_enc2icu_tbl[encoding];

src/include/access/gin.h

@@ -57,6 +57,9 @@ typedef struct GinStatsData
  */
 typedef char GinTernaryValue;
 
+StaticAssertDecl(sizeof(GinTernaryValue) == sizeof(bool),
+				 "sizes of GinTernaryValue and bool are not equal");
+
 #define GIN_FALSE		0		/* item is not present / does not match */
 #define GIN_TRUE		1		/* item is present / matches */
 #define GIN_MAYBE		2		/* don't know if item is present / don't know

src/include/access/htup_details.h

@@ -426,6 +426,9 @@ do { \
 	(tup)->t_choice.t_heap.t_field3.t_xvac = (xid); \
 } while (0)
 
+StaticAssertDecl(MaxOffsetNumber < SpecTokenOffsetNumber,
+				 "invalid speculative token constant");
+
 #define HeapTupleHeaderIsSpeculative(tup) \
 ( \
 	(ItemPointerGetOffsetNumberNoCheck(&(tup)->t_ctid) == SpecTokenOffsetNumber) \

src/include/access/nbtree.h

@@ -466,6 +466,13 @@ typedef struct BTVacState
 #define BT_PIVOT_HEAP_TID_ATTR		0x1000
 #define BT_IS_POSTING				0x2000
 
+/*
+ * Mask allocated for number of keys in index tuple must be able to fit
+ * maximum possible number of index attributes
+ */
+StaticAssertDecl(BT_OFFSET_MASK >= INDEX_MAX_KEYS,
+				 "BT_OFFSET_MASK can't fit INDEX_MAX_KEYS");
+
 /*
  * Note: BTreeTupleIsPivot() can have false negatives (but not false
  * positives) when used with !heapkeyspace indexes

src/include/c.h

@@ -847,47 +847,50 @@ extern void ExceptionalCondition(const char *conditionName,
  * If the "condition" (a compile-time-constant expression) evaluates to false,
  * throw a compile error using the "errmessage" (a string literal).
  *
- * gcc 4.6 and up supports _Static_assert(), but there are bizarre syntactic
+ * C11 has _Static_assert(), and most C99 compilers already support that.  For
- * placement restrictions.  Macros StaticAssertStmt() and StaticAssertExpr()
+ * portability, we wrap it into StaticAssertDecl().  _Static_assert() is a
+ * "declaration", and so it must be placed where for example a variable
+ * declaration would be valid.  As long as we compile with
+ * -Wno-declaration-after-statement, that also means it cannot be placed after
+ * statements in a function.  Macros StaticAssertStmt() and StaticAssertExpr()
  * make it safe to use as a statement or in an expression, respectively.
- * The macro StaticAssertDecl() is suitable for use at file scope (outside of
- * any function).
  *
- * Otherwise we fall back on a kluge that assumes the compiler will complain
+ * For compilers without _Static_assert(), we fall back on a kluge that
- * about a negative width for a struct bit-field.  This will not include a
+ * assumes the compiler will complain about a negative width for a struct
- * helpful error message, but it beats not getting an error at all.
+ * bit-field.  This will not include a helpful error message, but it beats not
+ * getting an error at all.
  */
 #ifndef __cplusplus
 #ifdef HAVE__STATIC_ASSERT
+#define StaticAssertDecl(condition, errmessage) \
+	_Static_assert(condition, errmessage)
 #define StaticAssertStmt(condition, errmessage) \
 	do { _Static_assert(condition, errmessage); } while(0)
 #define StaticAssertExpr(condition, errmessage) \
 	((void) ({ StaticAssertStmt(condition, errmessage); true; }))
-#define StaticAssertDecl(condition, errmessage) \
-	_Static_assert(condition, errmessage)
 #else							/* !HAVE__STATIC_ASSERT */
+#define StaticAssertDecl(condition, errmessage) \
+	extern void static_assert_func(int static_assert_failure[(condition) ? 1 : -1])
 #define StaticAssertStmt(condition, errmessage) \
 	((void) sizeof(struct { int static_assert_failure : (condition) ? 1 : -1; }))
 #define StaticAssertExpr(condition, errmessage) \
 	StaticAssertStmt(condition, errmessage)
-#define StaticAssertDecl(condition, errmessage) \
-	extern void static_assert_func(int static_assert_failure[(condition) ? 1 : -1])
 #endif							/* HAVE__STATIC_ASSERT */
 #else							/* C++ */
 #if defined(__cpp_static_assert) && __cpp_static_assert >= 200410
+#define StaticAssertDecl(condition, errmessage) \
+	static_assert(condition, errmessage)
 #define StaticAssertStmt(condition, errmessage) \
 	static_assert(condition, errmessage)
 #define StaticAssertExpr(condition, errmessage) \
 	({ static_assert(condition, errmessage); })
-#define StaticAssertDecl(condition, errmessage) \
-	static_assert(condition, errmessage)
 #else							/* !__cpp_static_assert */
+#define StaticAssertDecl(condition, errmessage) \
+	extern void static_assert_func(int static_assert_failure[(condition) ? 1 : -1])
 #define StaticAssertStmt(condition, errmessage) \
 	do { struct static_assert_struct { int static_assert_failure : (condition) ? 1 : -1; }; } while(0)
 #define StaticAssertExpr(condition, errmessage) \
 	((void) ({ StaticAssertStmt(condition, errmessage); }))
-#define StaticAssertDecl(condition, errmessage) \
-	extern void static_assert_func(int static_assert_failure[(condition) ? 1 : -1])
 #endif							/* __cpp_static_assert */
 #endif							/* C++ */
 

src/include/catalog/pg_control.h

@@ -247,4 +247,12 @@ typedef struct ControlFileData
  */
 #define PG_CONTROL_FILE_SIZE		8192
 
+/*
+ * Ensure that the size of the pg_control data structure is sane.
+ */
+StaticAssertDecl(sizeof(ControlFileData) <= PG_CONTROL_MAX_SAFE_SIZE,
+				 "pg_control is too large for atomic disk writes");
+StaticAssertDecl(sizeof(ControlFileData) <= PG_CONTROL_FILE_SIZE,
+				 "sizeof(ControlFileData) exceeds PG_CONTROL_FILE_SIZE");
+
 #endif							/* PG_CONTROL_H */

src/include/common/int128.h

@@ -177,7 +177,7 @@ static inline void
 int128_add_int64_mul_int64(INT128 *i128, int64 x, int64 y)
 {
 	/* INT64_AU32 must use arithmetic right shift */
-	StaticAssertStmt(((int64) -1 >> 1) == (int64) -1,
+	StaticAssertDecl(((int64) -1 >> 1) == (int64) -1,
 					 "arithmetic right shift is needed");
 
 	/*----------

src/include/storage/lwlock.h

@@ -59,6 +59,9 @@ typedef struct LWLock
  */
 #define LWLOCK_PADDED_SIZE	PG_CACHE_LINE_SIZE
 
+StaticAssertDecl(sizeof(LWLock) <= LWLOCK_PADDED_SIZE,
+				 "Miscalculated LWLock padding");
+
 /* LWLock, padded to a full cache line size */
 typedef union LWLockPadded
 {