Tom Lane wrote:
A nonterminal that is not intended to represent any real input, ever,
is just plain weird.


If you say so... PL/PgSQL already uses such a beast, though: the lno nonterminal, for example.

Not at all.  The right way to do this, I think, is for the mid-rule
action to palloc the PLpgSQL_exception_block, fill the variables into
that, and return the block as its semantic value.  The end-of-rule
action then picks up the block and adds what it needs to.

Ah, I see -- that makes sense. Attached is a revised patch -- applied to HEAD.

-Neil
Index: doc/src/sgml/plpgsql.sgml
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/doc/src/sgml/plpgsql.sgml,v
retrieving revision 1.70
diff -c -r1.70 plpgsql.sgml
*** doc/src/sgml/plpgsql.sgml	7 Jun 2005 02:47:15 -0000	1.70
--- doc/src/sgml/plpgsql.sgml	10 Jun 2005 15:34:04 -0000
***************
*** 2110,2115 ****
--- 2110,2126 ----
        don't use <literal>EXCEPTION</> without need.
       </para>
      </tip>
+ 
+     <para>
+      Within an exception handler, the <varname>SQLSTATE</varname>
+      variable contains the error code that corresponds to the
+      exception that was raised (refer to <xref
+      linkend="errcodes-table"> for a list of possible error
+      codes). The <varname>SQLERRM</varname> variable contains the
+      error message associated with the exception. These variables are
+      undefined outside exception handlers.
+     </para>
+ 
      <example id="plpgsql-upsert-example">
      <title>Exceptions with UPDATE/INSERT</title>
      <para>
Index: src/backend/utils/error/elog.c
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/backend/utils/error/elog.c,v
retrieving revision 1.159
diff -c -r1.159 elog.c
*** src/backend/utils/error/elog.c	9 Jun 2005 22:29:52 -0000	1.159
--- src/backend/utils/error/elog.c	10 Jun 2005 15:34:04 -0000
***************
*** 1482,1487 ****
--- 1482,1507 ----
  	}
  }
  
+ /*
+  * Unpack MAKE_SQLSTATE code. Note that this returns a pointer to a
+  * static buffer.
+  */
+ char *
+ unpack_sql_state(int sql_state)
+ {
+ 	static char	buf[12];
+ 	int			i;
+ 
+ 	for (i = 0; i < 5; i++)
+ 	{
+ 		buf[i] = PGUNSIXBIT(sql_state);
+ 		sql_state >>= 6;
+ 	}
+ 
+ 	buf[i] = '\0';
+ 	return buf;
+ }
+ 
  
  /*
   * Write error report to server's log
***************
*** 1497,1517 ****
  	appendStringInfo(&buf, "%s:  ", error_severity(edata->elevel));
  
  	if (Log_error_verbosity >= PGERROR_VERBOSE)
! 	{
! 		/* unpack MAKE_SQLSTATE code */
! 		char		tbuf[12];
! 		int			ssval;
! 		int			i;
! 
! 		ssval = edata->sqlerrcode;
! 		for (i = 0; i < 5; i++)
! 		{
! 			tbuf[i] = PGUNSIXBIT(ssval);
! 			ssval >>= 6;
! 		}
! 		tbuf[i] = '\0';
! 		appendStringInfo(&buf, "%s: ", tbuf);
! 	}
  
  	if (edata->message)
  		append_with_tabs(&buf, edata->message);
--- 1517,1523 ----
  	appendStringInfo(&buf, "%s:  ", error_severity(edata->elevel));
  
  	if (Log_error_verbosity >= PGERROR_VERBOSE)
! 		appendStringInfo(&buf, "%s: ", unpack_sql_state(edata->sqlerrcode));
  
  	if (edata->message)
  		append_with_tabs(&buf, edata->message);
Index: src/include/utils/elog.h
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/include/utils/elog.h,v
retrieving revision 1.78
diff -c -r1.78 elog.h
*** src/include/utils/elog.h	31 Dec 2004 22:03:46 -0000	1.78
--- src/include/utils/elog.h	10 Jun 2005 15:34:04 -0000
***************
*** 282,287 ****
--- 282,288 ----
  
  /* Other exported functions */
  extern void DebugFileOpen(void);
+ extern char *unpack_sql_state(int sql_state);
  
  /*
   * Write errors to stderr (or by equal means when stderr is
Index: src/pl/plpgsql/src/gram.y
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/pl/plpgsql/src/gram.y,v
retrieving revision 1.74
diff -c -r1.74 gram.y
*** src/pl/plpgsql/src/gram.y	8 Jun 2005 00:49:36 -0000	1.74
--- src/pl/plpgsql/src/gram.y	10 Jun 2005 16:02:48 -0000
***************
*** 92,97 ****
--- 92,98 ----
  		PLpgSQL_stmt_block		*program;
  		PLpgSQL_condition		*condition;
  		PLpgSQL_exception		*exception;
+ 		PLpgSQL_exception_block	*exception_block;
  		PLpgSQL_nsitem			*nsitem;
  		PLpgSQL_diag_item		*diagitem;
  }
***************
*** 129,135 ****
  %type <stmt>	stmt_dynexecute stmt_getdiag
  %type <stmt>	stmt_open stmt_fetch stmt_close stmt_null
  
! %type <list>	exception_sect proc_exceptions
  %type <exception>	proc_exception
  %type <condition>	proc_conditions
  
--- 130,137 ----
  %type <stmt>	stmt_dynexecute stmt_getdiag
  %type <stmt>	stmt_open stmt_fetch stmt_close stmt_null
  
! %type <list>	proc_exceptions
! %type <exception_block> exception_sect
  %type <exception>	proc_exception
  %type <condition>	proc_conditions
  
***************
*** 1495,1503 ****
  				;
  
  exception_sect	:
! 					{ $$ = NIL; }
! 				| K_EXCEPTION proc_exceptions
! 					{ $$ = $2; }
  				;
  
  proc_exceptions	: proc_exceptions proc_exception
--- 1497,1534 ----
  				;
  
  exception_sect	:
! 					{ $$ = NULL; }
! 				| K_EXCEPTION lno
! 					{
! 						/*
! 						 * We use a mid-rule action to add these
! 						 * special variables to the namespace before
! 						 * parsing the WHEN clauses themselves.
! 						 */
! 						PLpgSQL_exception_block *new = palloc(sizeof(PLpgSQL_exception_block));
! 						PLpgSQL_variable *var;
! 
! 						var = plpgsql_build_variable("sqlstate", $2,
! 													 plpgsql_build_datatype(TEXTOID, -1),
! 													 true);
! 						((PLpgSQL_var *) var)->isconst = true;
! 						new->sqlstate_varno = var->dno;
! 
! 						var = plpgsql_build_variable("sqlerrm", $2,
! 													 plpgsql_build_datatype(TEXTOID, -1),
! 													 true);
! 						((PLpgSQL_var *) var)->isconst = true;
! 						new->sqlerrm_varno = var->dno;
! 
! 						$<exception_block>$ = new;
! 					}
! 					proc_exceptions
! 					{
! 						PLpgSQL_exception_block *new = $<exception_block>3;
! 						new->exc_list = $4;
! 
! 						$$ = new;
! 					}
  				;
  
  proc_exceptions	: proc_exceptions proc_exception
Index: src/pl/plpgsql/src/pl_comp.c
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/pl/plpgsql/src/pl_comp.c,v
retrieving revision 1.90
diff -c -r1.90 pl_comp.c
*** src/pl/plpgsql/src/pl_comp.c	29 May 2005 04:23:06 -0000	1.90
--- src/pl/plpgsql/src/pl_comp.c	10 Jun 2005 15:34:04 -0000
***************
*** 656,662 ****
  	if (num_out_args > 0 || function->fn_rettype == VOIDOID ||
  		function->fn_retset)
  	{
! 		if (function->action->exceptions != NIL)
  		{
  			PLpgSQL_stmt_block *new;
  
--- 656,662 ----
  	if (num_out_args > 0 || function->fn_rettype == VOIDOID ||
  		function->fn_retset)
  	{
! 		if (function->action->exceptions != NULL)
  		{
  			PLpgSQL_stmt_block *new;
  
***************
*** 882,888 ****
  	}
  
  	/*
! 	 * Do a lookup on the compilers namestack
  	 */
  	nse = plpgsql_ns_lookup(cp[0], NULL);
  	if (nse != NULL)
--- 882,888 ----
  	}
  
  	/*
! 	 * Do a lookup on the compiler's namestack
  	 */
  	nse = plpgsql_ns_lookup(cp[0], NULL);
  	if (nse != NULL)
***************
*** 1935,1941 ****
  
  /* ----------
   * plpgsql_adddatum			Add a variable, record or row
!  *					to the compilers datum list.
   * ----------
   */
  void
--- 1935,1941 ----
  
  /* ----------
   * plpgsql_adddatum			Add a variable, record or row
!  *					to the compiler's datum list.
   * ----------
   */
  void
Index: src/pl/plpgsql/src/pl_exec.c
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/pl/plpgsql/src/pl_exec.c,v
retrieving revision 1.142
diff -c -r1.142 pl_exec.c
*** src/pl/plpgsql/src/pl_exec.c	7 Jun 2005 02:47:17 -0000	1.142
--- src/pl/plpgsql/src/pl_exec.c	10 Jun 2005 15:34:04 -0000
***************
*** 180,186 ****
  static void exec_init_tuple_store(PLpgSQL_execstate *estate);
  static bool compatible_tupdesc(TupleDesc td1, TupleDesc td2);
  static void exec_set_found(PLpgSQL_execstate *estate, bool state);
! 
  
  /* ----------
   * plpgsql_exec_function	Called by the call handler for
--- 180,186 ----
  static void exec_init_tuple_store(PLpgSQL_execstate *estate);
  static bool compatible_tupdesc(TupleDesc td1, TupleDesc td2);
  static void exec_set_found(PLpgSQL_execstate *estate, bool state);
! static void free_var(PLpgSQL_var *var);
  
  /* ----------
   * plpgsql_exec_function	Called by the call handler for
***************
*** 760,771 ****
  				{
  					PLpgSQL_var *var = (PLpgSQL_var *) (estate->datums[n]);
  
! 					if (var->freeval)
! 					{
! 						pfree((void *) (var->value));
! 						var->freeval = false;
! 					}
! 
  					if (!var->isconst || var->isnull)
  					{
  						if (var->default_val == NULL)
--- 760,766 ----
  				{
  					PLpgSQL_var *var = (PLpgSQL_var *) (estate->datums[n]);
  
! 					free_var(var);
  					if (!var->isconst || var->isnull)
  					{
  						if (var->default_val == NULL)
***************
*** 864,876 ****
  			SPI_restore_connection();
  
  			/* Look for a matching exception handler */
! 			foreach (e, block->exceptions)
  			{
  				PLpgSQL_exception *exception = (PLpgSQL_exception *) lfirst(e);
  
  				if (exception_matches_conditions(edata, exception->conditions))
  				{
  					rc = exec_stmts(estate, exception->action);
  					break;
  				}
  			}
--- 859,895 ----
  			SPI_restore_connection();
  
  			/* Look for a matching exception handler */
! 			foreach (e, block->exceptions->exc_list)
  			{
  				PLpgSQL_exception *exception = (PLpgSQL_exception *) lfirst(e);
  
  				if (exception_matches_conditions(edata, exception->conditions))
  				{
+ 					/*
+ 					 * Initialize the magic SQLSTATE and SQLERRM
+ 					 * variables for the exception block. We needn't
+ 					 * do this until we have found a matching
+ 					 * exception.
+ 					 */
+ 					PLpgSQL_var *state_var;
+ 					PLpgSQL_var *errm_var;
+ 
+ 					state_var = (PLpgSQL_var *) (estate->datums[block->exceptions->sqlstate_varno]);
+ 					state_var->value = DirectFunctionCall1(textin,
+ 														   CStringGetDatum(unpack_sql_state(edata->sqlerrcode)));
+ 					state_var->freeval = true;
+ 					state_var->isnull = false;
+ 
+ 					errm_var = (PLpgSQL_var *) (estate->datums[block->exceptions->sqlerrm_varno]);
+ 					errm_var->value = DirectFunctionCall1(textin,
+ 														  CStringGetDatum(edata->message));
+ 					errm_var->freeval = true;
+ 					errm_var->isnull = false;
+ 
  					rc = exec_stmts(estate, exception->action);
+ 
+ 					free_var(state_var);
+ 					free_var(errm_var);
  					break;
  				}
  			}
***************
*** 2586,2594 ****
  		 * Store the eventually assigned cursor name in the cursor variable
  		 * ----------
  		 */
! 		if (curvar->freeval)
! 			pfree((void *) (curvar->value));
! 
  		curvar->value = DirectFunctionCall1(textin, CStringGetDatum(portal->name));
  		curvar->isnull = false;
  		curvar->freeval = true;
--- 2605,2611 ----
  		 * Store the eventually assigned cursor name in the cursor variable
  		 * ----------
  		 */
! 		free_var(curvar);
  		curvar->value = DirectFunctionCall1(textin, CStringGetDatum(portal->name));
  		curvar->isnull = false;
  		curvar->freeval = true;
***************
*** 2684,2692 ****
  	 * Store the eventually assigned portal name in the cursor variable
  	 * ----------
  	 */
! 	if (curvar->freeval)
! 		pfree((void *) (curvar->value));
! 
  	curvar->value = DirectFunctionCall1(textin, CStringGetDatum(portal->name));
  	curvar->isnull = false;
  	curvar->freeval = true;
--- 2701,2707 ----
  	 * Store the eventually assigned portal name in the cursor variable
  	 * ----------
  	 */
! 	free_var(curvar);
  	curvar->value = DirectFunctionCall1(textin, CStringGetDatum(portal->name));
  	curvar->isnull = false;
  	curvar->freeval = true;
***************
*** 2857,2867 ****
  							 errmsg("NULL cannot be assigned to variable \"%s\" declared NOT NULL",
  									var->refname)));
  
! 				if (var->freeval)
! 				{
! 					pfree(DatumGetPointer(var->value));
! 					var->freeval = false;
! 				}
  
  				/*
  				 * If type is by-reference, make sure we have a freshly
--- 2872,2878 ----
  							 errmsg("NULL cannot be assigned to variable \"%s\" declared NOT NULL",
  									var->refname)));
  
! 				free_var(var);
  
  				/*
  				 * If type is by-reference, make sure we have a freshly
***************
*** 4343,4345 ****
--- 4354,4366 ----
  		FreeExecutorState(simple_eval_estate);
  	simple_eval_estate = NULL;
  }
+ 
+ static void
+ free_var(PLpgSQL_var *var)
+ {
+ 	if (var->freeval)
+ 	{
+ 		pfree(DatumGetPointer(var->value));
+ 		var->freeval = false;
+ 	}
+ }
Index: src/pl/plpgsql/src/pl_funcs.c
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/pl/plpgsql/src/pl_funcs.c,v
retrieving revision 1.40
diff -c -r1.40 pl_funcs.c
*** src/pl/plpgsql/src/pl_funcs.c	5 Apr 2005 06:22:16 -0000	1.40
--- src/pl/plpgsql/src/pl_funcs.c	10 Jun 2005 15:34:04 -0000
***************
*** 634,640 ****
  	{
  		ListCell *e;
  
! 		foreach (e, block->exceptions)
  		{
  			PLpgSQL_exception *exc = (PLpgSQL_exception *) lfirst(e);
  			PLpgSQL_condition *cond;
--- 634,640 ----
  	{
  		ListCell *e;
  
! 		foreach (e, block->exceptions->exc_list)
  		{
  			PLpgSQL_exception *exc = (PLpgSQL_exception *) lfirst(e);
  			PLpgSQL_condition *cond;
Index: src/pl/plpgsql/src/plpgsql.h
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/pl/plpgsql/src/plpgsql.h,v
retrieving revision 1.61
diff -c -r1.61 plpgsql.h
*** src/pl/plpgsql/src/plpgsql.h	7 Jun 2005 02:47:18 -0000	1.61
--- src/pl/plpgsql/src/plpgsql.h	10 Jun 2005 15:34:04 -0000
***************
*** 323,328 ****
--- 323,335 ----
  } PLpgSQL_condition;
  
  typedef struct
+ {
+ 	int			sqlstate_varno;
+ 	int			sqlerrm_varno;
+ 	List	   *exc_list;		/* List of WHEN clauses */
+ } PLpgSQL_exception_block;
+ 
+ typedef struct
  {								/* One EXCEPTION ... WHEN clause */
  	int			lineno;
  	PLpgSQL_condition *conditions;
***************
*** 336,344 ****
  	int			lineno;
  	char	   *label;
  	List	   *body;			/* List of statements */
- 	List	   *exceptions;		/* List of WHEN clauses */
  	int			n_initvars;
  	int		   *initvarnos;
  } PLpgSQL_stmt_block;
  
  
--- 343,351 ----
  	int			lineno;
  	char	   *label;
  	List	   *body;			/* List of statements */
  	int			n_initvars;
  	int		   *initvarnos;
+ 	PLpgSQL_exception_block *exceptions;
  } PLpgSQL_stmt_block;
  
  
Index: src/test/regress/expected/plpgsql.out
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/test/regress/expected/plpgsql.out,v
retrieving revision 1.32
diff -c -r1.32 plpgsql.out
*** src/test/regress/expected/plpgsql.out	7 Jun 2005 02:47:20 -0000	1.32
--- src/test/regress/expected/plpgsql.out	10 Jun 2005 15:34:04 -0000
***************
*** 2415,2417 ****
--- 2415,2471 ----
  
  drop table eifoo cascade;
  drop type eitype cascade;
+ --
+ -- SQLSTATE and SQLERRM test
+ --
+ -- should fail: SQLSTATE and SQLERRM are only in defined EXCEPTION
+ -- blocks
+ create function excpt_test() returns void as $$
+ begin
+     raise notice '% %', sqlstate, sqlerrm;
+ end; $$ language plpgsql;
+ ERROR:  syntax error at or near "sqlstate" at character 79
+ LINE 3:     raise notice '% %', sqlstate, sqlerrm;
+                                 ^
+ -- should fail
+ create function excpt_test() returns void as $$
+ begin
+     begin
+         begin
+     	    raise notice '% %', sqlstate, sqlerrm;
+         end;
+     end;
+ end; $$ language plpgsql;
+ ERROR:  syntax error at or near "sqlstate" at character 108
+ LINE 5:          raise notice '% %', sqlstate, sqlerrm;
+                                      ^
+ create function excpt_test() returns void as $$
+ begin
+     begin
+     	raise exception 'user exception';
+     exception when others then
+ 	    raise notice 'caught exception % %', sqlstate, sqlerrm;
+ 	    begin
+ 	        raise notice '% %', sqlstate, sqlerrm;
+ 	        perform 10/0;
+         exception
+             when substring_error then
+                 -- this exception handler shouldn't be invoked
+                 raise notice 'unexpected exception: % %', sqlstate, sqlerrm;
+ 	        when division_by_zero then
+ 	            raise notice 'caught exception % %', sqlstate, sqlerrm;
+ 	    end;
+ 	    raise notice '% %', sqlstate, sqlerrm;
+     end;
+ end; $$ language plpgsql;
+ select excpt_test();
+ NOTICE:  caught exception P0001 user exception
+ NOTICE:  P0001 user exception
+ NOTICE:  caught exception 22012 division by zero
+ NOTICE:  P0001 user exception
+  excpt_test 
+ ------------
+  
+ (1 row)
+ 
+ drop function excpt_test();
Index: src/test/regress/sql/plpgsql.sql
===================================================================
RCS file: /Users/neilc/local/cvs/pgsql/src/test/regress/sql/plpgsql.sql,v
retrieving revision 1.27
diff -c -r1.27 plpgsql.sql
*** src/test/regress/sql/plpgsql.sql	7 Jun 2005 02:47:23 -0000	1.27
--- src/test/regress/sql/plpgsql.sql	10 Jun 2005 15:34:04 -0000
***************
*** 2050,2052 ****
--- 2050,2096 ----
  
  drop table eifoo cascade;
  drop type eitype cascade;
+ 
+ --
+ -- SQLSTATE and SQLERRM test
+ --
+ 
+ -- should fail: SQLSTATE and SQLERRM are only in defined EXCEPTION
+ -- blocks
+ create function excpt_test() returns void as $$
+ begin
+     raise notice '% %', sqlstate, sqlerrm;
+ end; $$ language plpgsql;
+ 
+ -- should fail
+ create function excpt_test() returns void as $$
+ begin
+     begin
+         begin
+     	    raise notice '% %', sqlstate, sqlerrm;
+         end;
+     end;
+ end; $$ language plpgsql;
+ 
+ create function excpt_test() returns void as $$
+ begin
+     begin
+     	raise exception 'user exception';
+     exception when others then
+ 	    raise notice 'caught exception % %', sqlstate, sqlerrm;
+ 	    begin
+ 	        raise notice '% %', sqlstate, sqlerrm;
+ 	        perform 10/0;
+         exception
+             when substring_error then
+                 -- this exception handler shouldn't be invoked
+                 raise notice 'unexpected exception: % %', sqlstate, sqlerrm;
+ 	        when division_by_zero then
+ 	            raise notice 'caught exception % %', sqlstate, sqlerrm;
+ 	    end;
+ 	    raise notice '% %', sqlstate, sqlerrm;
+     end;
+ end; $$ language plpgsql;
+ 
+ select excpt_test();
+ drop function excpt_test();
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