Allow CURRENT/SESSION_USER to be used in certain commands

Commands such as ALTER USER, ALTER GROUP, ALTER ROLE, GRANT, and the
various ALTER OBJECT / OWNER TO, as well as ad-hoc clauses related to
roles such as the AUTHORIZATION clause of CREATE SCHEMA, the FOR clause
of CREATE USER MAPPING, and the FOR ROLE clause of ALTER DEFAULT
PRIVILEGES can now take the keywords CURRENT_USER and SESSION_USER as
user specifiers in place of an explicit user name.

This commit also fixes some quite ugly handling of special standards-
mandated syntax in CREATE USER MAPPING, which in particular would fail
to work in presence of a role named "current_user".

The special role specifiers PUBLIC and NONE also have more consistent
handling now.

Also take the opportunity to add location tracking to user specifiers.

Authors: Kyotaro Horiguchi.  Heavily reworked by Álvaro Herrera.
Reviewed by: Rushabh Lathia, Adam Brightwell, Marti Raudsepp.

1 files changed, 28 insertions, 30 deletions

diff --git a/src/backend/commands/foreigncmds.c b/src/backend/commands/foreigncmds.c
index bd4839189e6..3b85c2c017e 100644
--- a/src/backend/commands/foreigncmds.c
+++ b/src/backend/commands/foreigncmds.c
@@ -198,24 +198,6 @@ transformGenericOptions(Oid catalogId,
 
 
 /*
- * Convert the user mapping user name to OID
- */
-static Oid
-GetUserOidFromMapping(const char *username, bool missing_ok)
-{
-	if (!username)
-		/* PUBLIC user mapping */
-		return InvalidOid;
-
-	if (strcmp(username, "current_user") == 0)
-		/* map to the owner */
-		return GetUserId();
-
-	/* map to provided user */
-	return get_role_oid(username, missing_ok);
-}
-
-/*
  * Internal workhorse for changing a data wrapper's owner.
  *
  * Allow this only for superusers; also the new owner must be a
@@ -1156,10 +1138,14 @@ CreateUserMapping(CreateUserMappingStmt *stmt)
 	ObjectAddress referenced;
 	ForeignServer *srv;
 	ForeignDataWrapper *fdw;
+	RoleSpec   *role = (RoleSpec *) stmt->user;
 
 	rel = heap_open(UserMappingRelationId, RowExclusiveLock);
 
-	useId = GetUserOidFromMapping(stmt->username, false);
+	if (role->roletype == ROLESPEC_PUBLIC)
+		useId = ACL_ID_PUBLIC;
+	else
+		useId = get_rolespec_oid(stmt->user, false);
 
 	/* Check that the server exists. */
 	srv = GetForeignServerByName(stmt->servername, false);
@@ -1252,10 +1238,15 @@ AlterUserMapping(AlterUserMappingStmt *stmt)
 	Oid			umId;
 	ForeignServer *srv;
 	ObjectAddress address;
+	RoleSpec   *role = (RoleSpec *) stmt->user;
 
 	rel = heap_open(UserMappingRelationId, RowExclusiveLock);
 
-	useId = GetUserOidFromMapping(stmt->username, false);
+	if (role->roletype == ROLESPEC_PUBLIC)
+		useId = ACL_ID_PUBLIC;
+	else
+		useId = get_rolespec_oid(stmt->user, false);
+
 	srv = GetForeignServerByName(stmt->servername, false);
 
 	umId = GetSysCacheOid2(USERMAPPINGUSERSERVER,
@@ -1338,20 +1329,27 @@ RemoveUserMapping(DropUserMappingStmt *stmt)
 	Oid			useId;
 	Oid			umId;
 	ForeignServer *srv;
+	RoleSpec   *role = (RoleSpec *) stmt->user;
 
-	useId = GetUserOidFromMapping(stmt->username, stmt->missing_ok);
-	srv = GetForeignServerByName(stmt->servername, true);
-
-	if (stmt->username && !OidIsValid(useId))
+	if (role->roletype == ROLESPEC_PUBLIC)
+		useId = ACL_ID_PUBLIC;
+	else
 	{
-		/*
-		 * IF EXISTS specified, role not found and not public. Notice this and
-		 * leave.
-		 */
-		elog(NOTICE, "role \"%s\" does not exist, skipping", stmt->username);
-		return InvalidOid;
+		useId = get_rolespec_oid(stmt->user, stmt->missing_ok);
+		if (!OidIsValid(useId))
+		{
+			/*
+			 * IF EXISTS specified, role not found and not public. Notice this
+			 * and leave.
+			 */
+			elog(NOTICE, "role \"%s\" does not exist, skipping",
+				 role->rolename);
+			return InvalidOid;
+		}
 	}
 
+	srv = GetForeignServerByName(stmt->servername, true);
+
 	if (!srv)
 	{
 		if (!stmt->missing_ok)