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

1 files changed, 7 insertions, 6 deletions

diff --git a/src/backend/utils/adt/expandedrecord.c b/src/backend/utils/adt/expandedrecord.c
index b1b6883c19f..9aa6f3aac51 100644
--- a/src/backend/utils/adt/expandedrecord.c
+++ b/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;
 	}