Apply Tcl_Init() to the "hold" interpreter created by pltcl.

You might think this is unnecessary since that interpreter is never used
to run code --- but it turns out that's wrong.  As of Tcl 8.5, the "clock"
command (alone among builtin Tcl commands) is partially implemented by
loaded-on-demand Tcl code, which means that it fails if there's not
unknown-command support, and also that it's impossible to run it directly
in a safe interpreter.  The way they get around the latter is that
Tcl_CreateSlave() automatically sets up an alias command that forwards any
execution of "clock" in a safe slave interpreter to its parent interpreter.
Thus, when attempting to execute "clock" in trusted pltcl, the command
actually executes in the "hold" interpreter, where it will fail if
unknown-command support hasn't been introduced by sourcing the standard
init.tcl script, which is done by Tcl_Init().  (This is a pretty dubious
design decision on the Tcl boys' part, if you ask me ... but they didn't.)

Back-patch all the way.  It's not clear that anyone would try to use ancient
versions of pltcl with a recent Tcl, but it's not clear they wouldn't, either.
Also add a regression test using "clock", in branches that have regression
test support for pltcl.

Per recent trouble report from Kyle Bateman.

3 files changed, 36 insertions, 2 deletions

diff --git a/src/pl/tcl/expected/pltcl_setup.out b/src/pl/tcl/expected/pltcl_setup.out
index e168b121b86..7923ef5cdaf 100644
--- a/src/pl/tcl/expected/pltcl_setup.out
+++ b/src/pl/tcl/expected/pltcl_setup.out
@@ -402,3 +402,23 @@ create operator @< (
 		rightarg = int4,
 		procedure = tcl_int4lt
 	);
+--
+-- Test usage of Tcl's "clock" command.  In recent Tcl versions this
+-- command fails without working "unknown" support, so it's a good canary
+-- for initialization problems.
+--
+create function tcl_date_week(int4,int4,int4) returns text as '
+    return [clock format [clock scan "$2/$3/$1"] -format "%U"]
+' language pltcl immutable;
+select tcl_date_week(2010,1,24);
+ tcl_date_week 
+---------------
+ 04
+(1 row)
+
+select tcl_date_week(2001,10,24);
+ tcl_date_week 
+---------------
+ 42
+(1 row)
+
diff --git a/src/pl/tcl/pltcl.c b/src/pl/tcl/pltcl.c
index 3d118938a84..77e2b6b8d71 100644
--- a/src/pl/tcl/pltcl.c
+++ b/src/pl/tcl/pltcl.c
@@ -31,7 +31,7 @@
  *	  ENHANCEMENTS, OR MODIFICATIONS.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/tcl/pltcl.c,v 1.98.2.3 2008/06/17 00:53:04 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/tcl/pltcl.c,v 1.98.2.4 2010/01/25 01:58:40 tgl Exp $
  *
  **********************************************************************/
 
@@ -244,9 +244,12 @@ pltcl_init(void)
 	 ************************************************************/
 	if ((pltcl_hold_interp = Tcl_CreateInterp()) == NULL)
 		elog(ERROR, "could not create \"hold\" interpreter");
+	if (Tcl_Init(pltcl_hold_interp) == TCL_ERROR)
+		elog(ERROR, "could not initialize \"hold\" interpreter");
 
 	/************************************************************
-	 * Create the two interpreters
+	 * Create the two slave interpreters.  Note: Tcl automatically does
+	 * Tcl_Init on the normal slave, and it's not wanted for the safe slave.
 	 ************************************************************/
 	if ((pltcl_norm_interp =
 		 Tcl_CreateSlave(pltcl_hold_interp, "norm", 0)) == NULL)
diff --git a/src/pl/tcl/sql/pltcl_setup.sql b/src/pl/tcl/sql/pltcl_setup.sql
index 78ddd867eb4..17e09babb30 100644
--- a/src/pl/tcl/sql/pltcl_setup.sql
+++ b/src/pl/tcl/sql/pltcl_setup.sql
@@ -436,3 +436,14 @@ create operator @< (
 		procedure = tcl_int4lt
 	);
 
+--
+-- Test usage of Tcl's "clock" command.  In recent Tcl versions this
+-- command fails without working "unknown" support, so it's a good canary
+-- for initialization problems.
+--
+create function tcl_date_week(int4,int4,int4) returns text as '
+    return [clock format [clock scan "$2/$3/$1"] -format "%U"]
+' language pltcl immutable;
+
+select tcl_date_week(2010,1,24);
+select tcl_date_week(2001,10,24);