Add an OR REPLACE option to CREATE LANGUAGE.

This operates in the same way as other CREATE OR REPLACE commands, ie,
it replaces everything but the ownership and ACL lists of an existing
entry, and requires the caller to have owner privileges for that entry.

While modifying an existing language has some use in development scenarios,
in typical usage all the "replaced" values come from pg_pltemplate so there
will be no actual change in the language definition.  The reason for adding
this is mainly to allow programs to ensure that a language exists without
triggering an error if it already does exist.

This commit just adds and documents the new option.  A followon patch
will use it to clean up some unpleasant cases in pg_dump and pg_regress.

Author: tglsfdc

doc/src/sgml/ref/create_language.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/create_language.sgml,v 1.48 2009/12/19 01:49:02 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_language.sgml,v 1.49 2010/02/23 22:51:42 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -21,8 +21,8 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE [ PROCEDURAL ] LANGUAGE <replaceable class="parameter">name</replaceable>
-CREATE [ TRUSTED ] [ PROCEDURAL ] LANGUAGE <replaceable class="parameter">name</replaceable>
+CREATE [ OR REPLACE ] [ PROCEDURAL ] LANGUAGE <replaceable class="parameter">name</replaceable>
+CREATE [ OR REPLACE ] [ TRUSTED ] [ PROCEDURAL ] LANGUAGE <replaceable class="parameter">name</replaceable>
     HANDLER <replaceable class="parameter">call_handler</replaceable> [ INLINE <replaceable class="parameter">inline_handler</replaceable> ] [ VALIDATOR <replaceable>valfunction</replaceable> ]
 </synopsis>
  </refsynopsisdiv>
@@ -31,18 +31,17 @@ CREATE [ TRUSTED ] [ PROCEDURAL ] LANGUAGE <replaceable class="parameter">name</
   <title>Description</title>
 
   <para>
-   Using <command>CREATE LANGUAGE</command>, a
-   <productname>PostgreSQL</productname> user can register a new
+   <command>CREATE LANGUAGE</command> registers a new
    procedural language with a <productname>PostgreSQL</productname>
    database.  Subsequently, functions and trigger procedures can be
    defined in this new language.
   </para>
 
   <para>
    <command>CREATE LANGUAGE</command> effectively associates the
-   language name with a call handler that is responsible for executing
+   language name with handler function(s) that are responsible for executing
    functions written in the language.  Refer to <xref linkend="plhandler">
-   for more information about language call handlers.
+   for more information about language handlers.
   </para>
 
   <para>
@@ -77,6 +76,23 @@ CREATE [ TRUSTED ] [ PROCEDURAL ] LANGUAGE <replaceable class="parameter">name</
    The creator of a language becomes its owner and can later
    drop it, rename it, or assign it to a new owner.
   </para>
+
+  <para>
+   <command>CREATE OR REPLACE LANGUAGE</command> will either create a
+   new language, or replace an existing definition.  If the language
+   already exists, its parameters are updated according to the values
+   specified or taken from <structname>pg_pltemplate</structname>,
+   but the language's ownership and permissions settings do not change,
+   and any existing functions written in the language are assumed to still
+   be valid.  In addition to the normal privilege requirements for creating
+   a language, the user must be superuser or owner of the existing language.
+   The <literal>REPLACE</> case is mainly meant to be used to
+   ensure that the language exists.  If the language has a
+   <structname>pg_pltemplate</structname> entry then <literal>REPLACE</>
+   will not actually change anything about an existing definition, except in
+   the unusual case where the <structname>pg_pltemplate</structname> entry
+   has been modified since the language was created.
+  </para>
  </refsect1>
 
  <refsect1 id="sql-createlanguage-parameters">
@@ -88,7 +104,7 @@ CREATE [ TRUSTED ] [ PROCEDURAL ] LANGUAGE <replaceable class="parameter">name</
 
      <listitem>
       <para>
-       <literal>TRUSTED</literal> specifies that the call handler for
+       <literal>TRUSTED</literal> specifies that
        the language is safe, that is, it does not offer an
        unprivileged user any functionality to bypass access
        restrictions. If this key word is omitted when registering the

src/backend/commands/proclang.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/proclang.c,v 1.89 2010/02/14 18:42:14 rhaas Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/proclang.c,v 1.90 2010/02/23 22:51:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -17,7 +17,6 @@
 #include "access/heapam.h"
 #include "catalog/dependency.h"
 #include "catalog/indexing.h"
-#include "catalog/pg_authid.h"
 #include "catalog/pg_language.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_pltemplate.h"
@@ -49,7 +48,7 @@ typedef struct
 	char	   *tmpllibrary;	/* path of shared library */
 } PLTemplate;
 
-static void create_proc_lang(const char *languageName,
+static void create_proc_lang(const char *languageName, bool replace,
 				 Oid languageOwner, Oid handlerOid, Oid inlineOid,
 				 Oid valOid, bool trusted);
 static PLTemplate *find_language_template(const char *languageName);
@@ -73,16 +72,10 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 	Oid			funcargtypes[1];
 
 	/*
-	 * Translate the language name and check that this language doesn't
-	 * already exist
+	 * Translate the language name to lower case
 	 */
 	languageName = case_translate_language_name(stmt->plname);
 
-	if (SearchSysCacheExists1(LANGNAME, PointerGetDatum(languageName)))
-		ereport(ERROR,
-				(errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("language \"%s\" already exists", languageName)));
-
 	/*
 	 * If we have template information for the language, ignore the supplied
 	 * parameters (if any) and use the template information.
@@ -232,7 +225,8 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 			valOid = InvalidOid;
 
 		/* ok, create it */
-		create_proc_lang(languageName, GetUserId(), handlerOid, inlineOid,
+		create_proc_lang(languageName, stmt->replace, GetUserId(),
+						 handlerOid, inlineOid,
 						 valOid, pltemplate->tmpltrusted);
 	}
 	else
@@ -306,7 +300,8 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 			valOid = InvalidOid;
 
 		/* ok, create it */
-		create_proc_lang(languageName, GetUserId(), handlerOid, inlineOid,
+		create_proc_lang(languageName, stmt->replace, GetUserId(),
+						 handlerOid, inlineOid,
 						 valOid, stmt->pltrusted);
 	}
 }
@@ -315,27 +310,29 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
  * Guts of language creation.
  */
 static void
-create_proc_lang(const char *languageName,
+create_proc_lang(const char *languageName, bool replace,
 				 Oid languageOwner, Oid handlerOid, Oid inlineOid,
 				 Oid valOid, bool trusted)
 {
 	Relation	rel;
 	TupleDesc	tupDesc;
 	Datum		values[Natts_pg_language];
 	bool		nulls[Natts_pg_language];
+	bool		replaces[Natts_pg_language];
 	NameData	langname;
+	HeapTuple	oldtup;
 	HeapTuple	tup;
+	bool		is_update;
 	ObjectAddress myself,
 				referenced;
 
-	/*
-	 * Insert the new language into pg_language
-	 */
 	rel = heap_open(LanguageRelationId, RowExclusiveLock);
-	tupDesc = rel->rd_att;
+	tupDesc = RelationGetDescr(rel);
 
+	/* Prepare data to be inserted */
 	memset(values, 0, sizeof(values));
 	memset(nulls, false, sizeof(nulls));
+	memset(replaces, true, sizeof(replaces));
 
 	namestrcpy(&langname, languageName);
 	values[Anum_pg_language_lanname - 1] = NameGetDatum(&langname);
@@ -347,24 +344,62 @@ create_proc_lang(const char *languageName,
 	values[Anum_pg_language_lanvalidator - 1] = ObjectIdGetDatum(valOid);
 	nulls[Anum_pg_language_lanacl - 1] = true;
 
-	tup = heap_form_tuple(tupDesc, values, nulls);
+	/* Check for pre-existing definition */
+	oldtup = SearchSysCache1(LANGNAME, PointerGetDatum(languageName));
 
-	simple_heap_insert(rel, tup);
+	if (HeapTupleIsValid(oldtup))
+	{
+		/* There is one; okay to replace it? */
+		if (!replace)
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("language \"%s\" already exists", languageName)));
+		if (!pg_language_ownercheck(HeapTupleGetOid(oldtup), languageOwner))
+			aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_LANGUAGE,
+						   languageName);
 
+		/*
+		 * Do not change existing ownership or permissions.  Note
+		 * dependency-update code below has to agree with this decision.
+		 */
+		replaces[Anum_pg_language_lanowner - 1] = false;
+		replaces[Anum_pg_language_lanacl - 1] = false;
+
+		/* Okay, do it... */
+		tup = heap_modify_tuple(oldtup, tupDesc, values, nulls, replaces);
+		simple_heap_update(rel, &tup->t_self, tup);
+
+		ReleaseSysCache(oldtup);
+		is_update = true;
+	}
+	else
+	{
+		/* Creating a new language */
+		tup = heap_form_tuple(tupDesc, values, nulls);
+		simple_heap_insert(rel, tup);
+		is_update = false;
+	}
+
+	/* Need to update indexes for either the insert or update case */
 	CatalogUpdateIndexes(rel, tup);
 
 	/*
-	 * Create dependencies for language
+	 * Create dependencies for the new language.  If we are updating an
+	 * existing language, first delete any existing pg_depend entries.
+	 * (However, since we are not changing ownership or permissions, the
+	 * shared dependencies do *not* need to change, and we leave them alone.)
 	 */
 	myself.classId = LanguageRelationId;
 	myself.objectId = HeapTupleGetOid(tup);
 	myself.objectSubId = 0;
 
+	if (is_update)
+		deleteDependencyRecordsFor(myself.classId, myself.objectId);
+
 	/* dependency on owner of language */
-	referenced.classId = AuthIdRelationId;
-	referenced.objectId = languageOwner;
-	referenced.objectSubId = 0;
-	recordSharedDependencyOn(&myself, &referenced, SHARED_DEPENDENCY_OWNER);
+	if (!is_update)
+		recordDependencyOnOwner(myself.classId, myself.objectId,
+								languageOwner);
 
 	/* dependency on the PL handler function */
 	referenced.classId = ProcedureRelationId;

src/backend/nodes/copyfuncs.c

@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.462 2010/02/16 22:34:43 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.463 2010/02/23 22:51:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3237,6 +3237,7 @@ _copyCreatePLangStmt(CreatePLangStmt *from)
 {
 	CreatePLangStmt *newnode = makeNode(CreatePLangStmt);
 
+	COPY_SCALAR_FIELD(replace);
 	COPY_STRING_FIELD(plname);
 	COPY_NODE_FIELD(plhandler);
 	COPY_NODE_FIELD(plinline);

src/backend/nodes/equalfuncs.c

@@ -22,7 +22,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.383 2010/02/16 22:34:43 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.384 2010/02/23 22:51:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1710,6 +1710,7 @@ _equalDropPropertyStmt(DropPropertyStmt *a, DropPropertyStmt *b)
 static bool
 _equalCreatePLangStmt(CreatePLangStmt *a, CreatePLangStmt *b)
 {
+	COMPARE_SCALAR_FIELD(replace);
 	COMPARE_STRING_FIELD(plname);
 	COMPARE_NODE_FIELD(plhandler);
 	COMPARE_NODE_FIELD(plinline);

src/backend/parser/gram.y

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.710 2010/02/17 04:19:39 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.711 2010/02/23 22:51:42 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -2882,32 +2882,34 @@ NumericOnly:
 /*****************************************************************************
  *
  *		QUERIES :
- *				CREATE PROCEDURAL LANGUAGE ...
- *				DROP PROCEDURAL LANGUAGE ...
+ *				CREATE [OR REPLACE] [TRUSTED] [PROCEDURAL] LANGUAGE ...
+ *				DROP [PROCEDURAL] LANGUAGE ...
  *
  *****************************************************************************/
 
 CreatePLangStmt:
-			CREATE opt_trusted opt_procedural LANGUAGE ColId_or_Sconst
+			CREATE opt_or_replace opt_trusted opt_procedural LANGUAGE ColId_or_Sconst
 			{
 				CreatePLangStmt *n = makeNode(CreatePLangStmt);
-				n->plname = $5;
+				n->replace = $2;
+				n->plname = $6;
 				/* parameters are all to be supplied by system */
 				n->plhandler = NIL;
 				n->plinline = NIL;
 				n->plvalidator = NIL;
 				n->pltrusted = false;
 				$$ = (Node *)n;
 			}
-			| CREATE opt_trusted opt_procedural LANGUAGE ColId_or_Sconst
+			| CREATE opt_or_replace opt_trusted opt_procedural LANGUAGE ColId_or_Sconst
 			  HANDLER handler_name opt_inline_handler opt_validator
 			{
 				CreatePLangStmt *n = makeNode(CreatePLangStmt);
-				n->plname = $5;
-				n->plhandler = $7;
-				n->plinline = $8;
-				n->plvalidator = $9;
-				n->pltrusted = $2;
+				n->replace = $2;
+				n->plname = $6;
+				n->plhandler = $8;
+				n->plinline = $9;
+				n->plvalidator = $10;
+				n->pltrusted = $3;
 				$$ = (Node *)n;
 			}
 		;

src/include/nodes/parsenodes.h

@@ -13,7 +13,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/parsenodes.h,v 1.430 2010/02/16 22:34:57 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/parsenodes.h,v 1.431 2010/02/23 22:51:43 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1623,6 +1623,7 @@ typedef struct CreateTrigStmt
 typedef struct CreatePLangStmt
 {
 	NodeTag		type;
+	bool		replace;		/* T => replace if already exists */
 	char	   *plname;			/* PL name */
 	List	   *plhandler;		/* PL call handler function (qual. name) */
 	List	   *plinline;		/* optional inline function (qual. name) */