Improve makeArrayTypeName's algorithm for choosing array type names.

src/backend/catalog/pg_type.c

@@ -31,6 +31,7 @@
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
+#include "commands/defrem.h"
 #include "commands/typecmds.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
@@ -47,9 +48,6 @@
 #include "catalog/pg_type_encoding.h"
 #include "cdb/cdbvars.h"
 
-static char *makeUniqueTypeName(const char *typeName, Oid typeNamespace,
-								bool tryOriginal);
-
 /* GPDB_14_MERGE_FIXME: Do we need to keep binary_upgrade_next_pg_type_oid
  * for binary upgrade?
  */
@@ -964,16 +962,41 @@ RenameTypeInternal(Oid typeOid, const char *newTypeName, Oid typeNamespace)
 char *
 makeArrayTypeName(const char *typeName, Oid typeNamespace)
 {
-	char	   *arr;
+	char	   *arr_name;
+	int			pass = 0;
+	char		suffix[NAMEDATALEN];
 
-	arr = makeUniqueTypeName(typeName, typeNamespace, false);
-	if (arr == NULL)
-		ereport(ERROR,
-				(errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("could not form array type name for type \"%s\"",
-						typeName)));
+	/*
+	 * Per ancient Postgres tradition, array type names are made by prepending
+	 * an underscore to the base type name.  Much client code knows that
+	 * convention, so don't muck with it.  However, the tradition is less
+	 * clear about what to do in the corner cases where the resulting name is
+	 * too long or conflicts with an existing name.  Our current rules are (1)
+	 * truncate the base name on the right as needed, and (2) if there is a
+	 * conflict, append another underscore and some digits chosen to make it
+	 * unique.  This is similar to what ChooseRelationName() does.
+	 *
+	 * The actual name generation can be farmed out to makeObjectName() by
+	 * giving it an empty first name component.
+	 */
+
+	/* First, try with no numeric suffix */
+	arr_name = makeObjectName("", typeName, NULL);
+
+	for (;;)
+	{
+		if (!SearchSysCacheExists2(TYPENAMENSP,
+								   CStringGetDatum(arr_name),
+								   ObjectIdGetDatum(typeNamespace)))
+			break;
+
+		/* That attempt conflicted.  Prepare a new name with some digits. */
+		pfree(arr_name);
+		snprintf(suffix, sizeof(suffix), "%d", ++pass);
+		arr_name = makeObjectName("", typeName, suffix);
+	}
 
-	return arr;
+	return arr_name;
 }
 
 
@@ -1080,48 +1103,3 @@ makeMultirangeTypeName(const char *rangeTypeName, Oid typeNamespace)
 
 	return pstrdup(buf);
 }
-
-/*
- * makeUniqueTypeName
- *		Generate a unique name for a prospective new type
- *
- * Given a typeName, return a new palloc'ed name by prepending underscores
- * until a non-conflicting name results.
- *
- * If tryOriginal, first try with zero underscores.
- */
-static char *
-makeUniqueTypeName(const char *typeName, Oid typeNamespace, bool tryOriginal)
-{
-	int			i;
-	int			namelen;
-	char		dest[NAMEDATALEN];
-
-	Assert(strlen(typeName) <= NAMEDATALEN - 1);
-
-	if (tryOriginal &&
-		!SearchSysCacheExists2(TYPENAMENSP,
-							   CStringGetDatum(typeName),
-							   ObjectIdGetDatum(typeNamespace)))
-		return pstrdup(typeName);
-
-	/*
-	 * The idea is to prepend underscores as needed until we make a name that
-	 * doesn't collide with anything ...
-	 */
-	namelen = strlen(typeName);
-	for (i = 1; i < NAMEDATALEN - 1; i++)
-	{
-		dest[i - 1] = '_';
-		strlcpy(dest + i, typeName, NAMEDATALEN - i);
-		if (namelen + i >= NAMEDATALEN)
-			truncate_identifier(dest, NAMEDATALEN, false);
-
-		if (!SearchSysCacheExists2(TYPENAMENSP,
-								   CStringGetDatum(dest),
-								   ObjectIdGetDatum(typeNamespace)))
-			return pstrdup(dest);
-	}
-
-	return NULL;
-}

src/test/regress/expected/alter_table.out

@@ -202,9 +202,9 @@ SELECT typname FROM pg_type WHERE oid = 'attmp_array[]'::regtype;
 (1 row)
 
 SELECT typname FROM pg_type WHERE oid = '_attmp_array[]'::regtype;
-    typname     
-----------------
- ___attmp_array
+     typname     
+-----------------
+ __attmp_array_1
 (1 row)
 
 DROP TABLE _attmp_array;