Split CollateClause into separate raw and analyzed node types.

CollateClause is now used only in raw grammar output, and CollateExpr after
parse analysis.  This is for clarity and to avoid carrying collation names
in post-analysis parse trees: that's both wasteful and possibly misleading,
since the collation's name could be changed while the parsetree still
exists.

Also, clean up assorted infelicities and omissions in processing of the
node type.

src/backend/parser/gram.y

@@ -1993,8 +1993,7 @@ opt_collate_clause:
 				{
 					CollateClause *n = makeNode(CollateClause);
 					n->arg = NULL;
-					n->collnames = $2;
-					n->collOid = InvalidOid;
+					n->collname = $2;
 					n->location = @1;
 					$$ = (Node *) n;
 				}
@@ -2537,8 +2536,7 @@ ColConstraint:
 					 */
 					CollateClause *n = makeNode(CollateClause);
 					n->arg = NULL;
-					n->collnames = $2;
-					n->collOid = InvalidOid;
+					n->collname = $2;
 					n->location = @1;
 					$$ = (Node *) n;
 				}
@@ -9690,8 +9688,8 @@ a_expr:		c_expr									{ $$ = $1; }
 			| a_expr COLLATE any_name
 				{
 					CollateClause *n = makeNode(CollateClause);
-					n->arg = (Expr *) $1;
-					n->collnames = $3;
+					n->arg = $1;
+					n->collname = $3;
 					n->location = @2;
 					$$ = (Node *) n;
 				}

src/backend/parser/parse_coerce.c

@@ -279,11 +279,17 @@ coerce_type(ParseState *pstate, Node *node,
 		if (result)
 			return result;
 	}
-	if (IsA(node, CollateClause))
+	if (IsA(node, CollateExpr))
 	{
-		CollateClause *cc = (CollateClause *) node;
+		/*
+		 * XXX very ugly kluge to push the coercion underneath the CollateExpr.
+		 * This needs to be rethought, as it almost certainly doesn't cover
+		 * all cases.
+		 */
+		CollateExpr *cc = (CollateExpr *) node;
 
-		cc->arg = (Expr *) coerce_type(pstate, (Node *) cc->arg, inputTypeId, targetTypeId, targetTypeMod,
+		cc->arg = (Expr *) coerce_type(pstate, (Node *) cc->arg,
+									   inputTypeId, targetTypeId, targetTypeMod,
 									   ccontext, cformat, location);
 		return (Node *) cc;
 	}
@@ -2121,7 +2127,7 @@ select_common_collation(ParseState *pstate, List *exprs, bool none_ok)
 	{
 		Node	   *pexpr = (Node *) lfirst(lc);
 		Oid			pcoll = exprCollation(pexpr);
-		bool		pexplicit = IsA(pexpr, CollateClause);
+		bool		pexplicit = IsA(pexpr, CollateExpr);
 
 		if (pcoll && pexplicit)
 		{
@@ -2130,7 +2136,7 @@ select_common_collation(ParseState *pstate, List *exprs, bool none_ok)
 			{
 				Node	   *nexpr = (Node *) lfirst(lc2);
 				Oid			ncoll = exprCollation(nexpr);
-				bool		nexplicit = IsA(nexpr, CollateClause);
+				bool		nexplicit = IsA(nexpr, CollateExpr);
 
 				if (!ncoll || !nexplicit)
 					continue;

src/backend/parser/parse_expr.c

@@ -318,6 +318,7 @@ transformExpr(ParseState *pstate, Node *expr)
 		case T_CoerceViaIO:
 		case T_ArrayCoerceExpr:
 		case T_ConvertRowtypeExpr:
+		case T_CollateExpr:
 		case T_CaseTestExpr:
 		case T_ArrayExpr:
 		case T_CoerceToDomain:
@@ -2103,11 +2104,11 @@ transformTypeCast(ParseState *pstate, TypeCast *tc)
 static Node *
 transformCollateClause(ParseState *pstate, CollateClause *c)
 {
-	CollateClause *newc;
+	CollateExpr *newc;
 	Oid		argtype;
 
-	newc = makeNode(CollateClause);
-	newc->arg = (Expr *) transformExpr(pstate, (Node *) c->arg);
+	newc = makeNode(CollateExpr);
+	newc->arg = (Expr *) transformExpr(pstate, c->arg);
 
 	argtype = exprType((Node *) newc->arg);
 	/*
@@ -2121,8 +2122,7 @@ transformCollateClause(ParseState *pstate, CollateClause *c)
 						format_type_be(argtype)),
 				 parser_errposition(pstate, c->location)));
 
-	newc->collOid = LookupCollation(pstate, c->collnames, c->location);
-	newc->collnames = c->collnames;
+	newc->collOid = LookupCollation(pstate, c->collname, c->location);
 	newc->location = c->location;
 
 	return (Node *) newc;

src/backend/parser/parse_target.c

@@ -1583,7 +1583,7 @@ FigureColnameInternal(Node *node, char **name)
 			}
 			break;
 		case T_CollateClause:
-			return FigureColnameInternal((Node *) ((CollateClause *) node)->arg, name);
+			return FigureColnameInternal(((CollateClause *) node)->arg, name);
 		case T_CaseExpr:
 			strength = FigureColnameInternal((Node *) ((CaseExpr *) node)->defresult,
 											 name);

src/backend/parser/parse_type.c

@@ -471,7 +471,7 @@ GetColumnDefCollation(ParseState *pstate, ColumnDef *coldef, Oid typeOid)
 	{
 		/* We have a raw COLLATE clause, so look up the collation */
 		location = coldef->collClause->location;
-		result = LookupCollation(pstate, coldef->collClause->collnames,
+		result = LookupCollation(pstate, coldef->collClause->collname,
 								 location);
 	}
 	else if (OidIsValid(coldef->collOid))

src/backend/parser/parse_utilcmd.c

@@ -2467,7 +2467,7 @@ transformColumnType(CreateStmtContext *cxt, ColumnDef *column)
 		Oid		collOid;
 
 		collOid = LookupCollation(cxt->pstate,
-								  column->collClause->collnames,
+								  column->collClause->collname,
 								  column->collClause->location);
 		/* Complain if COLLATE is applied to an uncollatable type */
 		if (!OidIsValid(typtup->typcollation))