Provide database object names as separate fields in error messages.

This patch addresses the problem that applications currently have to
extract object names from possibly-localized textual error messages,
if they want to know for example which index caused a UNIQUE_VIOLATION
failure.  It adds new error message fields to the wire protocol, which
can carry the name of a table, table column, data type, or constraint
associated with the error.  (Since the protocol spec has always instructed
clients to ignore unrecognized field types, this should not create any
compatibility problem.)

Support for providing these new fields has been added to just a limited set
of error reports (mainly, those in the "integrity constraint violation"
SQLSTATE class), but we will doubtless add them to more calls in future.

Pavel Stehule, reviewed and extensively revised by Peter Geoghegan, with
additional hacking by Tom Lane.

src/backend/access/nbtree/nbtinsert.c

@@ -393,7 +393,9 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
 										RelationGetRelationName(rel)),
 								 errdetail("Key %s already exists.",
 										   BuildIndexValueDescription(rel,
-														  values, isnull))));
+															values, isnull)),
+								 errtableconstraint(heapRel,
+											 RelationGetRelationName(rel))));
 					}
 				}
 				else if (all_dead)
@@ -455,7 +457,9 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
 				(errcode(ERRCODE_INTERNAL_ERROR),
 				 errmsg("failed to re-find tuple within index \"%s\"",
 						RelationGetRelationName(rel)),
-		errhint("This may be because of a non-immutable index expression.")));
+		 errhint("This may be because of a non-immutable index expression."),
+				 errtableconstraint(heapRel,
+									RelationGetRelationName(rel))));
 
 	if (nbuf != InvalidBuffer)
 		_bt_relbuf(rel, nbuf);
@@ -523,6 +527,8 @@ _bt_findinsertloc(Relation rel,
 	 * able to fit three items on every page, so restrict any one item to 1/3
 	 * the per-page available space. Note that at this point, itemsz doesn't
 	 * include the ItemId.
+	 *
+	 * NOTE: if you change this, see also the similar code in _bt_buildadd().
 	 */
 	if (itemsz > BTMaxItemSize(page))
 		ereport(ERROR,
@@ -533,7 +539,9 @@ _bt_findinsertloc(Relation rel,
 				   RelationGetRelationName(rel)),
 		errhint("Values larger than 1/3 of a buffer page cannot be indexed.\n"
 				"Consider a function index of an MD5 hash of the value, "
-				"or use full text indexing.")));
+				"or use full text indexing."),
+				 errtableconstraint(heapRel,
+									RelationGetRelationName(rel))));
 
 	/*----------
 	 * If we will need to split the page to put the item on this page,

src/backend/access/nbtree/nbtree.c

@@ -109,14 +109,14 @@ btbuild(PG_FUNCTION_ARGS)
 		elog(ERROR, "index \"%s\" already contains data",
 			 RelationGetRelationName(index));
 
-	buildstate.spool = _bt_spoolinit(index, indexInfo->ii_Unique, false);
+	buildstate.spool = _bt_spoolinit(heap, index, indexInfo->ii_Unique, false);
 
 	/*
 	 * If building a unique index, put dead tuples in a second spool to keep
 	 * them out of the uniqueness check.
 	 */
 	if (indexInfo->ii_Unique)
-		buildstate.spool2 = _bt_spoolinit(index, false, true);
+		buildstate.spool2 = _bt_spoolinit(heap, index, false, true);
 
 	/* do the heap scan */
 	reltuples = IndexBuildHeapScan(heap, index, indexInfo, true,

src/backend/access/nbtree/nbtsort.c

@@ -83,6 +83,7 @@
 struct BTSpool
 {
 	Tuplesortstate *sortstate;	/* state data for tuplesort.c */
+	Relation	heap;
 	Relation	index;
 	bool		isunique;
 };
@@ -116,6 +117,7 @@ typedef struct BTPageState
  */
 typedef struct BTWriteState
 {
+	Relation	heap;
 	Relation	index;
 	bool		btws_use_wal;	/* dump pages to WAL? */
 	BlockNumber btws_pages_alloced;		/* # pages allocated */
@@ -145,11 +147,12 @@ static void _bt_load(BTWriteState *wstate,
  * create and initialize a spool structure
  */
 BTSpool *
-_bt_spoolinit(Relation index, bool isunique, bool isdead)
+_bt_spoolinit(Relation heap, Relation index, bool isunique, bool isdead)
 {
 	BTSpool    *btspool = (BTSpool *) palloc0(sizeof(BTSpool));
 	int			btKbytes;
 
+	btspool->heap = heap;
 	btspool->index = index;
 	btspool->isunique = isunique;
 
@@ -162,7 +165,7 @@ _bt_spoolinit(Relation index, bool isunique, bool isdead)
 	 * work_mem.
 	 */
 	btKbytes = isdead ? work_mem : maintenance_work_mem;
-	btspool->sortstate = tuplesort_begin_index_btree(index, isunique,
+	btspool->sortstate = tuplesort_begin_index_btree(heap, index, isunique,
 													 btKbytes, false);
 
 	return btspool;
@@ -208,6 +211,7 @@ _bt_leafbuild(BTSpool *btspool, BTSpool *btspool2)
 	if (btspool2)
 		tuplesort_performsort(btspool2->sortstate);
 
+	wstate.heap = btspool->heap;
 	wstate.index = btspool->index;
 
 	/*
@@ -486,7 +490,9 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup)
 				   RelationGetRelationName(wstate->index)),
 		errhint("Values larger than 1/3 of a buffer page cannot be indexed.\n"
 				"Consider a function index of an MD5 hash of the value, "
-				"or use full text indexing.")));
+				"or use full text indexing."),
+				 errtableconstraint(wstate->heap,
+									RelationGetRelationName(wstate->index))));
 
 	/*
 	 * Check to see if page is "full".	It's definitely full if the item won't