Rework parsing of ConstraintAttributeSpec to improve NOT VALID handling.

The initial commit of the ALTER TABLE ADD FOREIGN KEY NOT VALID feature
failed to support labeling such constraints as deferrable.  The best fix
for this seems to be to fold NOT VALID into ConstraintAttributeSpec.
That's a bit more general than the documented syntax, but it allows
better-targeted syntax error messages.

In addition, do some mostly-but-not-entirely-cosmetic code review for
the whole NOT VALID patch.

Author: tglsfdc

doc/src/sgml/catalogs.sgml

@@ -1898,7 +1898,8 @@
       <entry><structfield>convalidated</structfield></entry>
       <entry><type>bool</type></entry>
       <entry></entry>
-      <entry>Has the constraint been validated? Can only be false for foreign keys</entry>
+      <entry>Has the constraint been validated?
+       Currently, can only be false for foreign keys</entry>
      </row>
 
      <row>

doc/src/sgml/ref/alter_table.sgml

@@ -42,9 +42,8 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET ( <replaceable class="PARAMETER">attribute_option</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> RESET ( <replaceable class="PARAMETER">attribute_option</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
-    ADD <replaceable class="PARAMETER">table_constraint</replaceable>
-    ADD <replaceable class="PARAMETER">table_constraint_using_index</replaceable>
     ADD <replaceable class="PARAMETER">table_constraint</replaceable> [ NOT VALID ]
+    ADD <replaceable class="PARAMETER">table_constraint_using_index</replaceable>
     VALIDATE CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable>
     DROP CONSTRAINT [ IF EXISTS ]  <replaceable class="PARAMETER">constraint_name</replaceable> [ RESTRICT | CASCADE ]
     DISABLE TRIGGER [ <replaceable class="PARAMETER">trigger_name</replaceable> | ALL | USER ]
@@ -235,27 +234,21 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
    </varlistentry>
 
    <varlistentry>
-    <term><literal>ADD <replaceable class="PARAMETER">table_constraint</replaceable>
-          [ NOT VALID ]</literal></term>
+    <term><literal>ADD <replaceable class="PARAMETER">table_constraint</replaceable> [ NOT VALID ]</literal></term>
     <listitem>
      <para>
       This form adds a new constraint to a table using the same syntax as
-      <xref linkend="SQL-CREATETABLE">. Newly added foreign key constraints can
-      also be defined as <literal>NOT VALID</literal> to avoid the
-      potentially lengthy initial check that must otherwise be performed.
-      Constraint checks are skipped at create table time, so
-      <xref linkend="SQL-CREATETABLE"> does not contain this option.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><literal>VALIDATE CONSTRAINT</literal></term>
-    <listitem>
-     <para>
-      This form validates a foreign key constraint that was previously created
-      as <literal>NOT VALID</literal>. Constraints already marked valid do not
-      cause an error response.
+      <xref linkend="SQL-CREATETABLE">, plus the option <literal>NOT
+      VALID</literal>, which is currently only allowed for foreign key
+      constraints.
+      If the constraint is marked <literal>NOT VALID</literal>, the
+      potentially-lengthy initial check to verify that all rows in the table
+      satisfy the constraint is skipped.  The constraint will still be
+      enforced against subsequent inserts or updates (that is, they'll fail
+      unless there is a matching row in the referenced table).  But the
+      database will not assume that the constraint holds for all rows in
+      the table, until it is validated by using the <literal>VALIDATE
+      CONSTRAINT</literal> option.
      </para>
     </listitem>
    </varlistentry>
@@ -311,6 +304,21 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>VALIDATE CONSTRAINT</literal></term>
+    <listitem>
+     <para>
+      This form validates a foreign key constraint that was previously created
+      as <literal>NOT VALID</literal>, by scanning the table to ensure there
+      are no unmatched rows.  Nothing happens if the constraint is
+      already marked valid.
+      The value of separating validation from initial creation of the
+      constraint is that validation requires a lesser lock on the table
+      than constraint creation does.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>DROP CONSTRAINT [ IF EXISTS ]</literal></term>
     <listitem>

src/backend/commands/tablecmds.c

@@ -258,7 +258,7 @@ static void AlterIndexNamespaces(Relation classRel, Relation rel,
 static void AlterSeqNamespaces(Relation classRel, Relation rel,
 				   Oid oldNspOid, Oid newNspOid,
 				   const char *newNspName, LOCKMODE lockmode);
-static void ATExecValidateConstraint(Relation rel, const char *constrName);
+static void ATExecValidateConstraint(Relation rel, char *constrName);
 static int transformColumnNameList(Oid relId, List *colList,
 						int16 *attnums, Oid *atttypids);
 static int transformFkeyGetPrimaryKey(Relation pkrel, Oid *indexOid,
@@ -5726,9 +5726,9 @@ ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
 	createForeignKeyTriggers(rel, fkconstraint, constrOid, indexOid);
 
 	/*
-	 * Tell Phase 3 to check that the constraint is satisfied by existing rows
-	 * We can skip this during table creation or if requested explicitly by
-	 * specifying NOT VALID on an alter table statement.
+	 * Tell Phase 3 to check that the constraint is satisfied by existing rows.
+	 * We can skip this during table creation, or if requested explicitly by
+	 * specifying NOT VALID in an ADD FOREIGN KEY command.
 	 */
 	if (!fkconstraint->skip_validation)
 	{
@@ -5755,7 +5755,7 @@ ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
  * ALTER TABLE VALIDATE CONSTRAINT
  */
 static void
-ATExecValidateConstraint(Relation rel, const char *constrName)
+ATExecValidateConstraint(Relation rel, char *constrName)
 {
 	Relation	conrel;
 	SysScanDesc scan;
@@ -5810,7 +5810,7 @@ ATExecValidateConstraint(Relation rel, const char *constrName)
 		 */
 		refrel = heap_open(con->confrelid, RowShareLock);
 
-		validateForeignKeyConstraint((char *) constrName, rel, refrel,
+		validateForeignKeyConstraint(constrName, rel, refrel,
 									 con->conindid,
 									 conid);
 
@@ -5830,6 +5830,7 @@ ATExecValidateConstraint(Relation rel, const char *constrName)
 	heap_close(conrel, RowExclusiveLock);
 }
 
+
 /*
  * transformColumnNameList - transform list of column names
  *

src/backend/commands/trigger.c

@@ -1006,6 +1006,8 @@ ConvertTriggerToFK(CreateTrigStmt *stmt, Oid funcoid)
 		}
 		fkcon->deferrable = stmt->deferrable;
 		fkcon->initdeferred = stmt->initdeferred;
+		fkcon->skip_validation = false;
+		fkcon->initially_valid = true;
 
 		/* ... and execute it */
 		ProcessUtility((Node *) atstmt,