Add const qualifiers where they are accidentally cast away

This only produces warnings under -Wcast-qual, but it's more correct
and consistent in any case.

contrib/intarray/_intbig_gist.c

@@ -332,7 +332,7 @@ typedef struct
 static int
 comparecost(const void *a, const void *b)
 {
-	return ((SPLITCOST *) a)->cost - ((SPLITCOST *) b)->cost;
+	return ((const SPLITCOST *) a)->cost - ((const SPLITCOST *) b)->cost;
 }
 
 

contrib/ltree/ltree_gist.c

@@ -275,8 +275,8 @@ static int
 treekey_cmp(const void *a, const void *b)
 {
 	return ltree_compare(
-						 ((RIX *) a)->r,
-						 ((RIX *) b)->r
+						 ((const RIX *) a)->r,
+						 ((const RIX *) b)->r
 		);
 }
 

src/backend/access/gist/gistproc.c

@@ -284,8 +284,8 @@ typedef struct
 static int
 interval_cmp_lower(const void *i1, const void *i2)
 {
-	double		lower1 = ((SplitInterval *) i1)->lower,
-				lower2 = ((SplitInterval *) i2)->lower;
+	double		lower1 = ((const SplitInterval *) i1)->lower,
+				lower2 = ((const SplitInterval *) i2)->lower;
 
 	if (lower1 < lower2)
 		return -1;
@@ -301,8 +301,8 @@ interval_cmp_lower(const void *i1, const void *i2)
 static int
 interval_cmp_upper(const void *i1, const void *i2)
 {
-	double		upper1 = ((SplitInterval *) i1)->upper,
-				upper2 = ((SplitInterval *) i2)->upper;
+	double		upper1 = ((const SplitInterval *) i1)->upper,
+				upper2 = ((const SplitInterval *) i2)->upper;
 
 	if (upper1 < upper2)
 		return -1;
@@ -455,8 +455,8 @@ box_penalty(BOX *original, BOX *new)
 static int
 common_entry_cmp(const void *i1, const void *i2)
 {
-	double		delta1 = ((CommonEntry *) i1)->delta,
-				delta2 = ((CommonEntry *) i2)->delta;
+	double		delta1 = ((const CommonEntry *) i1)->delta,
+				delta2 = ((const CommonEntry *) i2)->delta;
 
 	if (delta1 < delta2)
 		return -1;

src/backend/utils/adt/tsquery_util.c

@@ -134,7 +134,7 @@ QTNodeCompare(QTNode *an, QTNode *bn)
 static int
 cmpQTN(const void *a, const void *b)
 {
-	return QTNodeCompare(*(QTNode **) a, *(QTNode **) b);
+	return QTNodeCompare(*(QTNode * const *) a, *(QTNode * const *) b);
 }
 
 void

src/backend/utils/adt/xml.c

@@ -311,7 +311,7 @@ xml_recv(PG_FUNCTION_ARGS)
 	str = VARDATA(result);
 	str[nbytes] = '\0';
 
-	parse_xml_decl((xmlChar *) str, NULL, NULL, &encodingStr, NULL);
+	parse_xml_decl((const xmlChar *) str, NULL, NULL, &encodingStr, NULL);
 
 	/*
 	 * If encoding wasn't explicitly specified in the XML header, treat it as

src/backend/utils/misc/guc.c

@@ -3780,8 +3780,8 @@ find_option(const char *name, bool create_placeholders, int elevel)
 static int
 guc_var_compare(const void *a, const void *b)
 {
-	struct config_generic *confa = *(struct config_generic **) a;
-	struct config_generic *confb = *(struct config_generic **) b;
+	const struct config_generic *confa = *(struct config_generic * const *) a;
+	const struct config_generic *confb = *(struct config_generic * const *) b;
 
 	return guc_name_compare(confa->name, confb->name);
 }

src/bin/psql/mbprint.c

@@ -217,10 +217,10 @@ pg_wcssize(const unsigned char *pwcs, size_t len, int encoding,
 
 	for (; *pwcs && len > 0; pwcs += chlen)
 	{
-		chlen = PQmblen((char *) pwcs, encoding);
+		chlen = PQmblen((const char *) pwcs, encoding);
 		if (len < (size_t) chlen)
 			break;
-		w = PQdsplen((char *) pwcs, encoding);
+		w = PQdsplen((const char *) pwcs, encoding);
 
 		if (chlen == 1)			/* single-byte char */
 		{
@@ -298,10 +298,10 @@ pg_wcsformat(const unsigned char *pwcs, size_t len, int encoding,
 
 	for (; *pwcs && len > 0; pwcs += chlen)
 	{
-		chlen = PQmblen((char *) pwcs, encoding);
+		chlen = PQmblen((const char *) pwcs, encoding);
 		if (len < (size_t) chlen)
 			break;
-		w = PQdsplen((char *) pwcs, encoding);
+		w = PQdsplen((const char *) pwcs, encoding);
 
 		if (chlen == 1)			/* single-byte char */
 		{

src/include/c.h

@@ -478,7 +478,7 @@ typedef NameData *Name;
  * PointerIsValid
  *		True iff pointer is valid.
  */
-#define PointerIsValid(pointer) ((void*)(pointer) != NULL)
+#define PointerIsValid(pointer) ((const void*)(pointer) != NULL)
 
 /*
  * PointerIsAligned

src/include/utils/pg_crc.h

@@ -40,7 +40,7 @@ typedef uint32 pg_crc32;
 /* Accumulate some (more) bytes into a CRC */
 #define COMP_CRC32(crc, data, len)	\
 do { \
-	unsigned char *__data = (unsigned char *) (data); \
+	const unsigned char *__data = (const unsigned char *) (data); \
 	uint32		__len = (len); \
 \
 	while (__len-- > 0) \