Apply identity sequence values on COPY

A COPY into a table should apply identity sequence values just like it
does for ordinary defaults.  This was previously forgotten, leading to
null values being inserted, which in turn would fail because identity
columns have not-null constraints.

Author: Michael Paquier <michael.paquier@gmail.com>
Reported-by: Steven Winfield <steven.winfield@cantabcapital.com>
Bug: #14952

src/backend/commands/copy.c

@@ -23,6 +23,7 @@
 #include "access/sysattr.h"
 #include "access/xact.h"
 #include "access/xlog.h"
+#include "catalog/dependency.h"
 #include "catalog/pg_type.h"
 #include "commands/copy.h"
 #include "commands/defrem.h"
@@ -3067,8 +3068,19 @@ BeginCopyFrom(ParseState *pstate,
 		{
 			/* attribute is NOT to be copied from input */
 			/* use default value if one exists */
-			Expr	   *defexpr = (Expr *) build_column_default(cstate->rel,
+			Expr	   *defexpr;
+
+			if (att->attidentity)
+			{
+				NextValueExpr *nve = makeNode(NextValueExpr);
+
+				nve->seqid = getOwnedSequence(RelationGetRelid(cstate->rel),
 											  attnum);
+				nve->typeId = att->atttypid;
+				defexpr = (Expr *) nve;
+			}
+			else
+				defexpr = (Expr *) build_column_default(cstate->rel, attnum);
 
 			if (defexpr != NULL)
 			{

src/test/regress/expected/identity.out

@@ -153,6 +153,19 @@ SELECT * FROM itest2;
   3 | 
 (3 rows)
 
+-- COPY tests
+CREATE TABLE itest9 (a int GENERATED ALWAYS AS IDENTITY, b text, c bigint);
+COPY itest9 FROM stdin;
+COPY itest9 (b, c) FROM stdin;
+SELECT * FROM itest9 ORDER BY c;
+  a  |  b   |  c  
+-----+------+-----
+ 100 | foo  | 200
+ 101 | bar  | 201
+   1 | foo2 | 202
+   2 | bar2 | 203
+(4 rows)
+
 -- DROP IDENTITY tests
 ALTER TABLE itest4 ALTER COLUMN a DROP IDENTITY;
 ALTER TABLE itest4 ALTER COLUMN a DROP IDENTITY;  -- error

src/test/regress/sql/identity.sql

@@ -78,6 +78,23 @@ UPDATE itest2 SET a = DEFAULT WHERE a = 2;
 SELECT * FROM itest2;
 
 
+-- COPY tests
+
+CREATE TABLE itest9 (a int GENERATED ALWAYS AS IDENTITY, b text, c bigint);
+
+COPY itest9 FROM stdin;
+100	foo	200
+101	bar	201
+\.
+
+COPY itest9 (b, c) FROM stdin;
+foo2	202
+bar2	203
+\.
+
+SELECT * FROM itest9 ORDER BY c;
+
+
 -- DROP IDENTITY tests
 
 ALTER TABLE itest4 ALTER COLUMN a DROP IDENTITY;