Invent "amadjustmembers" AM method for validating opclass members.

This allows AM-specific knowledge to be applied during creation of
pg_amop and pg_amproc entries.  Specifically, the AM knows better than
core code which entries to consider as required or optional.  Giving
the latter entries the appropriate sort of dependency allows them to
be dropped without taking out the whole opclass or opfamily; which
is something we'd like to have to correct obsolescent entries in
extensions.

This callback also opens the door to performing AM-specific validity
checks during opclass creation, rather than hoping than an opclass
developer will remember to test with "amvalidate".  For the most part
I've not actually added any such checks yet; that can happen in a
follow-on patch.  (Note that we shouldn't remove any tests from
"amvalidate", as those are still needed to cross-check manually
constructed entries in the initdb data.  So adding tests to
"amadjustmembers" will be somewhat duplicative, but it seems like
a good idea anyway.)

Patch by me, reviewed by Alexander Korotkov, Hamid Akhtar, and
Anastasia Lubennikova.

Discussion: https://postgr.es/m/4578.1565195302@sss.pgh.pa.us

src/include/access/amapi.h

@@ -54,6 +54,42 @@ typedef enum IndexAMProperty
 	AMPROP_CAN_INCLUDE
 } IndexAMProperty;
 
+/*
+ * We use lists of this struct type to keep track of both operators and
+ * support functions while building or adding to an opclass or opfamily.
+ * amadjustmembers functions receive lists of these structs, and are allowed
+ * to alter their "ref" fields.
+ *
+ * The "ref" fields define how the pg_amop or pg_amproc entry should depend
+ * on the associated objects (that is, which dependency type to use, and
+ * which opclass or opfamily it should depend on).
+ *
+ * If ref_is_hard is true, the entry will have a NORMAL dependency on the
+ * operator or support func, and an INTERNAL dependency on the opclass or
+ * opfamily.  This forces the opclass or opfamily to be dropped if the
+ * operator or support func is dropped, and requires the CASCADE option
+ * to do so.  Nor will ALTER OPERATOR FAMILY DROP be allowed.  This is
+ * the right behavior for objects that are essential to an opclass.
+ *
+ * If ref_is_hard is false, the entry will have an AUTO dependency on the
+ * operator or support func, and also an AUTO dependency on the opclass or
+ * opfamily.  This allows ALTER OPERATOR FAMILY DROP, and causes that to
+ * happen automatically if the operator or support func is dropped.  This
+ * is the right behavior for inessential ("loose") objects.
+ */
+typedef struct OpFamilyMember
+{
+	bool		is_func;		/* is this an operator, or support func? */
+	Oid			object;			/* operator or support func's OID */
+	int			number;			/* strategy or support func number */
+	Oid			lefttype;		/* lefttype */
+	Oid			righttype;		/* righttype */
+	Oid			sortfamily;		/* ordering operator's sort opfamily, or 0 */
+	bool		ref_is_hard;	/* hard or soft dependency? */
+	bool		ref_is_family;	/* is dependency on opclass or opfamily? */
+	Oid			refobjid;		/* OID of opclass or opfamily */
+} OpFamilyMember;
+
 
 /*
  * Callback function signatures --- see indexam.sgml for more info.
@@ -114,6 +150,12 @@ typedef char *(*ambuildphasename_function) (int64 phasenum);
 /* validate definition of an opclass for this AM */
 typedef bool (*amvalidate_function) (Oid opclassoid);
 
+/* validate operators and support functions to be added to an opclass/family */
+typedef void (*amadjustmembers_function) (Oid opfamilyoid,
+										  Oid opclassoid,
+										  List *operators,
+										  List *functions);
+
 /* prepare for index scan */
 typedef IndexScanDesc (*ambeginscan_function) (Relation indexRelation,
 											   int nkeys,
@@ -224,6 +266,7 @@ typedef struct IndexAmRoutine
 	amproperty_function amproperty; /* can be NULL */
 	ambuildphasename_function ambuildphasename; /* can be NULL */
 	amvalidate_function amvalidate;
+	amadjustmembers_function amadjustmembers;	/* can be NULL */
 	ambeginscan_function ambeginscan;
 	amrescan_function amrescan;
 	amgettuple_function amgettuple; /* can be NULL */

src/include/access/amvalidate.h

@@ -1,7 +1,8 @@
 /*-------------------------------------------------------------------------
  *
  * amvalidate.h
- *	  Support routines for index access methods' amvalidate functions.
+ *	  Support routines for index access methods' amvalidate and
+ *	  amadjustmembers functions.
  *
  * Copyright (c) 2016-2020, PostgreSQL Global Development Group
  *
@@ -32,6 +33,8 @@ extern bool check_amproc_signature(Oid funcid, Oid restype, bool exact,
 extern bool check_amoptsproc_signature(Oid funcid);
 extern bool check_amop_signature(Oid opno, Oid restype,
 								 Oid lefttype, Oid righttype);
+extern Oid	opclass_for_family_datatype(Oid amoid, Oid opfamilyoid,
+										Oid datatypeoid);
 extern bool opfamily_can_sort_type(Oid opfamilyoid, Oid datatypeoid);
 
 #endif							/* AMVALIDATE_H */

src/include/access/gin_private.h

@@ -407,6 +407,10 @@ extern ItemPointer ginVacuumItemPointers(GinVacuumState *gvs,
 
 /* ginvalidate.c */
 extern bool ginvalidate(Oid opclassoid);
+extern void ginadjustmembers(Oid opfamilyoid,
+							 Oid opclassoid,
+							 List *operators,
+							 List *functions);
 
 /* ginbulk.c */
 typedef struct GinEntryAccumulator

src/include/access/gist_private.h

@@ -464,6 +464,10 @@ extern bool gistcanreturn(Relation index, int attno);
 
 /* gistvalidate.c */
 extern bool gistvalidate(Oid opclassoid);
+extern void gistadjustmembers(Oid opfamilyoid,
+							  Oid opclassoid,
+							  List *operators,
+							  List *functions);
 
 /* gistutil.c */
 

src/include/access/hash.h

@@ -379,6 +379,10 @@ extern IndexBulkDeleteResult *hashvacuumcleanup(IndexVacuumInfo *info,
 												IndexBulkDeleteResult *stats);
 extern bytea *hashoptions(Datum reloptions, bool validate);
 extern bool hashvalidate(Oid opclassoid);
+extern void hashadjustmembers(Oid opfamilyoid,
+							  Oid opclassoid,
+							  List *operators,
+							  List *functions);
 
 /* private routines */
 

src/include/access/nbtree.h

@@ -1141,6 +1141,10 @@ extern bool _bt_allequalimage(Relation rel, bool debugmessage);
  * prototypes for functions in nbtvalidate.c
  */
 extern bool btvalidate(Oid opclassoid);
+extern void btadjustmembers(Oid opfamilyoid,
+							Oid opclassoid,
+							List *operators,
+							List *functions);
 
 /*
  * prototypes for functions in nbtsort.c

src/include/access/spgist.h

@@ -220,5 +220,9 @@ extern IndexBulkDeleteResult *spgvacuumcleanup(IndexVacuumInfo *info,
 
 /* spgvalidate.c */
 extern bool spgvalidate(Oid opclassoid);
+extern void spgadjustmembers(Oid opfamilyoid,
+							 Oid opclassoid,
+							 List *operators,
+							 List *functions);
 
 #endif							/* SPGIST_H */