Correct constness of system attributes in heap.c & prerequisites.

This allows the compiler / linker to mark affected pages as read-only.

There's a fair number of pre-requisite changes, to allow the const
properly be propagated. Most of consts were already required for
correctness anyway, just not represented on the type-level.  Arguably
we could be more aggressive in using consts in related code, but..

This requires using a few of the types underlying typedefs that
removes pointers (e.g. const NameData *) as declaring the typedefed
type constant doesn't have the same meaning (it makes the variable
const, not what it points to).

Discussion: https://postgr.es/m/20181015200754.7y7zfuzsoux2c4ya@alap3.anarazel.de

src/backend/catalog/heap.c

@@ -144,7 +144,7 @@ static List *insert_ordered_unique_oid(List *list, Oid datum);
  * fixed-size portion of the structure anyway.
  */
 
-static FormData_pg_attribute a1 = {
+static const FormData_pg_attribute a1 = {
 	.attname = {"ctid"},
 	.atttypid = TIDOID,
 	.attlen = sizeof(ItemPointerData),
@@ -158,7 +158,7 @@ static FormData_pg_attribute a1 = {
 	.attislocal = true,
 };
 
-static FormData_pg_attribute a2 = {
+static const FormData_pg_attribute a2 = {
 	.attname = {"oid"},
 	.atttypid = OIDOID,
 	.attlen = sizeof(Oid),
@@ -172,7 +172,7 @@ static FormData_pg_attribute a2 = {
 	.attislocal = true,
 };
 
-static FormData_pg_attribute a3 = {
+static const FormData_pg_attribute a3 = {
 	.attname = {"xmin"},
 	.atttypid = XIDOID,
 	.attlen = sizeof(TransactionId),
@@ -186,7 +186,7 @@ static FormData_pg_attribute a3 = {
 	.attislocal = true,
 };
 
-static FormData_pg_attribute a4 = {
+static const FormData_pg_attribute a4 = {
 	.attname = {"cmin"},
 	.atttypid = CIDOID,
 	.attlen = sizeof(CommandId),
@@ -200,7 +200,7 @@ static FormData_pg_attribute a4 = {
 	.attislocal = true,
 };
 
-static FormData_pg_attribute a5 = {
+static const FormData_pg_attribute a5 = {
 	.attname = {"xmax"},
 	.atttypid = XIDOID,
 	.attlen = sizeof(TransactionId),
@@ -214,7 +214,7 @@ static FormData_pg_attribute a5 = {
 	.attislocal = true,
 };
 
-static FormData_pg_attribute a6 = {
+static const FormData_pg_attribute a6 = {
 	.attname = {"cmax"},
 	.atttypid = CIDOID,
 	.attlen = sizeof(CommandId),
@@ -234,7 +234,7 @@ static FormData_pg_attribute a6 = {
  * table of a particular class/type. In any case table is still the word
  * used in SQL.
  */
-static FormData_pg_attribute a7 = {
+static const FormData_pg_attribute a7 = {
 	.attname = {"tableoid"},
 	.atttypid = OIDOID,
 	.attlen = sizeof(Oid),
@@ -248,14 +248,14 @@ static FormData_pg_attribute a7 = {
 	.attislocal = true,
 };
 
-static const Form_pg_attribute SysAtt[] = {&a1, &a2, &a3, &a4, &a5, &a6, &a7};
+static const FormData_pg_attribute *SysAtt[] = {&a1, &a2, &a3, &a4, &a5, &a6, &a7};
 
 /*
  * This function returns a Form_pg_attribute pointer for a system attribute.
  * Note that we elog if the presented attno is invalid, which would only
  * happen if there's a problem upstream.
  */
-Form_pg_attribute
+const FormData_pg_attribute *
 SystemAttributeDefinition(AttrNumber attno, bool relhasoids)
 {
 	if (attno >= 0 || attno < -(int) lengthof(SysAtt))
@@ -269,14 +269,14 @@ SystemAttributeDefinition(AttrNumber attno, bool relhasoids)
  * If the given name is a system attribute name, return a Form_pg_attribute
  * pointer for a prototype definition.  If not, return NULL.
  */
-Form_pg_attribute
+const FormData_pg_attribute *
 SystemAttributeByName(const char *attname, bool relhasoids)
 {
 	int			j;
 
 	for (j = 0; j < (int) lengthof(SysAtt); j++)
 	{
-		Form_pg_attribute att = SysAtt[j];
+		const FormData_pg_attribute *att = SysAtt[j];
 
 		if (relhasoids || att->attnum != ObjectIdAttributeNumber)
 		{

src/backend/catalog/index.c

@@ -352,7 +352,7 @@ ConstructTupleDescriptor(Relation heapRelation,
 		if (atnum != 0)
 		{
 			/* Simple index column */
-			Form_pg_attribute from;
+			const FormData_pg_attribute *from;
 
 			if (atnum < 0)
 			{

src/backend/executor/spi.c

@@ -899,7 +899,7 @@ int
 SPI_fnumber(TupleDesc tupdesc, const char *fname)
 {
 	int			res;
-	Form_pg_attribute sysatt;
+	const FormData_pg_attribute *sysatt;
 
 	for (res = 0; res < tupdesc->natts; res++)
 	{
@@ -921,7 +921,7 @@ SPI_fnumber(TupleDesc tupdesc, const char *fname)
 char *
 SPI_fname(TupleDesc tupdesc, int fnumber)
 {
-	Form_pg_attribute att;
+	const FormData_pg_attribute *att;
 
 	SPI_result = 0;
 

src/backend/optimizer/util/plancat.c

@@ -1692,7 +1692,7 @@ build_index_tlist(PlannerInfo *root, IndexOptInfo *index,
 		if (indexkey != 0)
 		{
 			/* simple column */
-			Form_pg_attribute att_tup;
+			const FormData_pg_attribute *att_tup;
 
 			if (indexkey < 0)
 				att_tup = SystemAttributeDefinition(indexkey,

src/backend/parser/parse_relation.c

@@ -3135,7 +3135,7 @@ attnameAttNum(Relation rd, const char *attname, bool sysColOK)
 static int
 specialAttNum(const char *attname)
 {
-	Form_pg_attribute sysatt;
+	const FormData_pg_attribute *sysatt;
 
 	sysatt = SystemAttributeByName(attname,
 								   true /* "oid" will be accepted */ );
@@ -3152,12 +3152,12 @@ specialAttNum(const char *attname)
  *	heap_open()'ed.  Use the cache version get_atttype()
  *	for access to non-opened relations.
  */
-Name
+const NameData *
 attnumAttName(Relation rd, int attid)
 {
 	if (attid <= 0)
 	{
-		Form_pg_attribute sysatt;
+		const FormData_pg_attribute *sysatt;
 
 		sysatt = SystemAttributeDefinition(attid, rd->rd_rel->relhasoids);
 		return &sysatt->attname;
@@ -3179,7 +3179,7 @@ attnumTypeId(Relation rd, int attid)
 {
 	if (attid <= 0)
 	{
-		Form_pg_attribute sysatt;
+		const FormData_pg_attribute *sysatt;
 
 		sysatt = SystemAttributeDefinition(attid, rd->rd_rel->relhasoids);
 		return sysatt->atttypid;

src/backend/parser/parse_utilcmd.c

@@ -2065,7 +2065,7 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 		for (i = 0; i < index_form->indnatts; i++)
 		{
 			int16		attnum = index_form->indkey.values[i];
-			Form_pg_attribute attform;
+			const FormData_pg_attribute *attform;
 			char	   *attname;
 			Oid			defopclass;
 

src/backend/utils/adt/expandedrecord.c

@@ -1025,6 +1025,7 @@ expanded_record_lookup_field(ExpandedRecordHeader *erh, const char *fieldname,
 	TupleDesc	tupdesc;
 	int			fno;
 	Form_pg_attribute attr;
+	const FormData_pg_attribute *sysattr;
 
 	tupdesc = expanded_record_get_tupdesc(erh);
 
@@ -1044,13 +1045,13 @@ expanded_record_lookup_field(ExpandedRecordHeader *erh, const char *fieldname,
 	}
 
 	/* How about system attributes? */
-	attr = SystemAttributeByName(fieldname, tupdesc->tdhasoid);
-	if (attr != NULL)
+	sysattr = SystemAttributeByName(fieldname, tupdesc->tdhasoid);
+	if (sysattr != NULL)
 	{
-		finfo->fnumber = attr->attnum;
-		finfo->ftypeid = attr->atttypid;
-		finfo->ftypmod = attr->atttypmod;
-		finfo->fcollation = attr->attcollation;
+		finfo->fnumber = sysattr->attnum;
+		finfo->ftypeid = sysattr->atttypid;
+		finfo->ftypmod = sysattr->atttypmod;
+		finfo->fcollation = sysattr->attcollation;
 		return true;
 	}
 

src/backend/utils/adt/name.c

@@ -188,7 +188,7 @@ namege(PG_FUNCTION_ARGS)
 /* (see char.c for comparison/operation routines) */
 
 int
-namecpy(Name n1, Name n2)
+namecpy(Name n1, const NameData *n2)
 {
 	if (!n1 || !n2)
 		return -1;

src/include/catalog/heap.h

@@ -127,10 +127,10 @@ extern void RemoveAttrDefault(Oid relid, AttrNumber attnum,
 extern void RemoveAttrDefaultById(Oid attrdefId);
 extern void RemoveStatistics(Oid relid, AttrNumber attnum);
 
-extern Form_pg_attribute SystemAttributeDefinition(AttrNumber attno,
+extern const FormData_pg_attribute *SystemAttributeDefinition(AttrNumber attno,
 						  bool relhasoids);
 
-extern Form_pg_attribute SystemAttributeByName(const char *attname,
+extern const FormData_pg_attribute *SystemAttributeByName(const char *attname,
 					  bool relhasoids);
 
 extern void CheckAttributeNamesTypes(TupleDesc tupdesc, char relkind,

src/include/parser/parse_relation.h

@@ -125,7 +125,7 @@ extern void expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
 extern List *expandRelAttrs(ParseState *pstate, RangeTblEntry *rte,
 			   int rtindex, int sublevels_up, int location);
 extern int	attnameAttNum(Relation rd, const char *attname, bool sysColOK);
-extern Name attnumAttName(Relation rd, int attid);
+extern const NameData *attnumAttName(Relation rd, int attid);
 extern Oid	attnumTypeId(Relation rd, int attid);
 extern Oid	attnumCollationId(Relation rd, int attid);
 extern bool isQueryUsingTempRelation(Query *query);

src/include/utils/builtins.h

@@ -37,7 +37,7 @@ extern unsigned hex_decode(const char *src, unsigned len, char *dst);
 extern int2vector *buildint2vector(const int16 *int2s, int n);
 
 /* name.c */
-extern int	namecpy(Name n1, Name n2);
+extern int	namecpy(Name n1, const NameData *n2);
 extern int	namestrcpy(Name name, const char *str);
 extern int	namestrcmp(Name name, const char *str);