Allow default expressions to be attached to columns of foreign tables.

There's still some discussion about exactly how postgres_fdw ought to
handle this case, but there seems no debate that we want to allow defaults
to be used for inserts into foreign tables.  So remove the core-code
restrictions that prevented it.

While at it, get rid of the special grammar productions for CREATE FOREIGN
TABLE, and instead add explicit FEATURE_NOT_SUPPORTED error checks for the
disallowed cases.  This makes the grammar a shade smaller, and more
importantly results in much more intelligible error messages for
unsupported cases.  It's also one less thing to fix if we ever start
supporting constraints on foreign tables.

3 files changed, 62 insertions, 47 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 47b6233a80..8bb8f54ae5 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -465,7 +465,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId)
 	if (stmt->constraints != NIL && relkind == RELKIND_FOREIGN_TABLE)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("constraints on foreign tables are not supported")));
+				 errmsg("constraints are not supported on foreign tables")));
 
 	/*
 	 * Look up the namespace in which we are supposed to create the relation,
@@ -588,11 +588,6 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId)
 		{
 			RawColumnDefault *rawEnt;
 
-			if (relkind == RELKIND_FOREIGN_TABLE)
-				ereport(ERROR,
-						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-						 errmsg("default values on foreign tables are not supported")));
-
 			Assert(colDef->cooked_default == NULL);
 
 			rawEnt = (RawColumnDefault *) palloc(sizeof(RawColumnDefault));
@@ -2978,7 +2973,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			 * substitutes default values into INSERTs before it expands
 			 * rules.
 			 */
-			ATSimplePermissions(rel, ATT_TABLE | ATT_VIEW);
+			ATSimplePermissions(rel, ATT_TABLE | ATT_VIEW | ATT_FOREIGN_TABLE);
 			ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
 			/* No command-specific prep needed */
 			pass = cmd->def ? AT_PASS_ADD_CONSTR : AT_PASS_DROP;
@@ -4528,11 +4523,6 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	{
 		RawColumnDefault *rawEnt;
 
-		if (relkind == RELKIND_FOREIGN_TABLE)
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-			  errmsg("default values on foreign tables are not supported")));
-
 		rawEnt = (RawColumnDefault *) palloc(sizeof(RawColumnDefault));
 		rawEnt->attnum = attribute.attnum;
 		rawEnt->raw_default = copyObject(colDef->raw_default);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 0787d2f506..9d07f30906 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -330,7 +330,6 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>	stmtblock stmtmulti
 				OptTableElementList TableElementList OptInherit definition
 				OptTypedTableElementList TypedTableElementList
-				OptForeignTableElementList ForeignTableElementList
 				reloptions opt_reloptions
 				OptWith opt_distinct opt_definition func_args func_args_list
 				func_args_with_defaults func_args_with_defaults_list
@@ -408,7 +407,6 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <vsetstmt> set_rest set_rest_more SetResetClause FunctionSetResetClause
 
 %type <node>	TableElement TypedTableElement ConstraintElem TableFuncElement
-				ForeignTableElement
 %type <node>	columnDef columnOptions
 %type <defelt>	def_elem reloption_elem old_aggr_elem
 %type <node>	def_arg columnElem where_clause where_or_current_clause
@@ -4137,57 +4135,37 @@ AlterForeignServerStmt: ALTER SERVER name foreign_server_version alter_generic_o
 
 CreateForeignTableStmt:
 		CREATE FOREIGN TABLE qualified_name
-			OptForeignTableElementList
+			'(' OptTableElementList ')'
 			SERVER name create_generic_options
 				{
 					CreateForeignTableStmt *n = makeNode(CreateForeignTableStmt);
 					$4->relpersistence = RELPERSISTENCE_PERMANENT;
 					n->base.relation = $4;
-					n->base.tableElts = $5;
+					n->base.tableElts = $6;
 					n->base.inhRelations = NIL;
 					n->base.if_not_exists = false;
 					/* FDW-specific data */
-					n->servername = $7;
-					n->options = $8;
+					n->servername = $9;
+					n->options = $10;
 					$$ = (Node *) n;
 				}
 		| CREATE FOREIGN TABLE IF_P NOT EXISTS qualified_name
-			OptForeignTableElementList
+			'(' OptTableElementList ')'
 			SERVER name create_generic_options
 				{
 					CreateForeignTableStmt *n = makeNode(CreateForeignTableStmt);
 					$7->relpersistence = RELPERSISTENCE_PERMANENT;
 					n->base.relation = $7;
-					n->base.tableElts = $8;
+					n->base.tableElts = $9;
 					n->base.inhRelations = NIL;
 					n->base.if_not_exists = true;
 					/* FDW-specific data */
-					n->servername = $10;
-					n->options = $11;
+					n->servername = $12;
+					n->options = $13;
 					$$ = (Node *) n;
 				}
 		;
 
-OptForeignTableElementList:
-			'(' ForeignTableElementList ')'			{ $$ = $2; }
-			| '(' ')'								{ $$ = NIL; }
-		;
-
-ForeignTableElementList:
-			ForeignTableElement
-				{
-					$$ = list_make1($1);
-				}
-			| ForeignTableElementList ',' ForeignTableElement
-				{
-					$$ = lappend($1, $3);
-				}
-		;
-
-ForeignTableElement:
-			columnDef					{ $$ = $1; }
-		;
-
 /*****************************************************************************
  *
  *		QUERY:
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index 8a1876c8a3..4fdcf180fa 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -70,6 +70,7 @@ typedef struct
 	RangeVar   *relation;		/* relation to create */
 	Relation	rel;			/* opened/locked rel, if ALTER */
 	List	   *inhRelations;	/* relations to inherit from */
+	bool		isforeign;		/* true if CREATE/ALTER FOREIGN TABLE */
 	bool		isalter;		/* true if altering existing table */
 	bool		hasoids;		/* does relation have an OID column? */
 	List	   *columns;		/* ColumnDef items */
@@ -195,9 +196,15 @@ transformCreateStmt(CreateStmt *stmt, const char *queryString)
 
 	cxt.pstate = pstate;
 	if (IsA(stmt, CreateForeignTableStmt))
+	{
 		cxt.stmtType = "CREATE FOREIGN TABLE";
+		cxt.isforeign = true;
+	}
 	else
+	{
 		cxt.stmtType = "CREATE TABLE";
+		cxt.isforeign = false;
+	}
 	cxt.relation = stmt->relation;
 	cxt.rel = NULL;
 	cxt.inhRelations = stmt->inhRelations;
@@ -515,11 +522,23 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
 				break;
 
 			case CONSTR_CHECK:
+				if (cxt->isforeign)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("constraints are not supported on foreign tables"),
+							 parser_errposition(cxt->pstate,
+												constraint->location)));
 				cxt->ckconstraints = lappend(cxt->ckconstraints, constraint);
 				break;
 
 			case CONSTR_PRIMARY:
 			case CONSTR_UNIQUE:
+				if (cxt->isforeign)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("constraints are not supported on foreign tables"),
+							 parser_errposition(cxt->pstate,
+												constraint->location)));
 				if (constraint->keys == NIL)
 					constraint->keys = list_make1(makeString(column->colname));
 				cxt->ixconstraints = lappend(cxt->ixconstraints, constraint);
@@ -531,7 +550,12 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
 				break;
 
 			case CONSTR_FOREIGN:
-
+				if (cxt->isforeign)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("constraints are not supported on foreign tables"),
+							 parser_errposition(cxt->pstate,
+												constraint->location)));
 				/*
 				 * Fill in the current attribute's name and throw it into the
 				 * list of FK constraints to be processed later.
@@ -555,8 +579,8 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
 	}
 
 	/*
-	 * Generate ALTER FOREIGN TABLE ALTER COLUMN statement which adds
-	 * per-column foreign data wrapper options for this column.
+	 * If needed, generate ALTER FOREIGN TABLE ALTER COLUMN statement to add
+	 * per-column foreign data wrapper options to this column after creation.
 	 */
 	if (column->fdwoptions != NIL)
 	{
@@ -587,6 +611,13 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
 static void
 transformTableConstraint(CreateStmtContext *cxt, Constraint *constraint)
 {
+	if (cxt->isforeign)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("constraints are not supported on foreign tables"),
+				 parser_errposition(cxt->pstate,
+									constraint->location)));
+
 	switch (constraint->contype)
 	{
 		case CONSTR_PRIMARY:
@@ -640,7 +671,14 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
 	char	   *comment;
 	ParseCallbackState pcbstate;
 
-	setup_parser_errposition_callback(&pcbstate, cxt->pstate, table_like_clause->relation->location);
+	setup_parser_errposition_callback(&pcbstate, cxt->pstate,
+									  table_like_clause->relation->location);
+
+	/* we could support LIKE in many cases, but worry about it another day */
+	if (cxt->isforeign)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("LIKE is not supported for foreign tables")));
 
 	relation = relation_openrv(table_like_clause->relation, AccessShareLock);
 
@@ -2334,7 +2372,16 @@ transformAlterTableStmt(AlterTableStmt *stmt, const char *queryString)
 	pstate->p_sourcetext = queryString;
 
 	cxt.pstate = pstate;
-	cxt.stmtType = "ALTER TABLE";
+	if (stmt->relkind == OBJECT_FOREIGN_TABLE)
+	{
+		cxt.stmtType = "ALTER FOREIGN TABLE";
+		cxt.isforeign = true;
+	}
+	else
+	{
+		cxt.stmtType = "ALTER TABLE";
+		cxt.isforeign = false;
+	}
 	cxt.relation = stmt->relation;
 	cxt.rel = rel;
 	cxt.inhRelations = NIL;