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

3 files changed, 13 insertions, 0 deletions

diff --git a/src/include/access/gin.h b/src/include/access/gin.h
index fff861e219..119ed685bb 100644
--- a/src/include/access/gin.h
+++ b/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
diff --git a/src/include/access/htup_details.h b/src/include/access/htup_details.h
index 9561c835f2..c1af814e8d 100644
--- a/src/include/access/htup_details.h
+++ b/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) \
diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h
index 8e4f6864e5..7d5a6fa558 100644
--- a/src/include/access/nbtree.h
+++ b/src/include/access/nbtree.h
@@ -467,6 +467,13 @@ typedef struct BTVacState
 #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
  */