Add control knobs for plpgsql's variable resolution behavior, and make the

default be "throw error on conflict", as per discussions.  The GUC variable
is plpgsql.variable_conflict, with values "error", "use_variable",
"use_column".  The behavior can also be specified per-function by inserting
one of
	#variable_conflict error
	#variable_conflict use_variable
	#variable_conflict use_column
at the start of the function body.

The 8.5 release notes will need to mention using "use_variable" to retain
backward-compatible behavior, although we should encourage people to migrate
to the much less mistake-prone "error" setting.

Update the plpgsql documentation to match this and other recent changes.

doc/src/sgml/config.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.232 2009/10/21 20:38:58 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.233 2009/11/13 22:43:39 tgl Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -5162,8 +5162,8 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
      when using custom variables:
 
 <programlisting>
-custom_variable_classes = 'plr,plperl'
-plr.path = '/usr/lib/R'
+custom_variable_classes = 'plpgsql,plperl'
+plpgsql.variable_conflict = use_variable
 plperl.use_strict = true
 plruby.use_strict = true        # generates error: unknown class name
 </programlisting>

src/pl/plpgsql/src/gram.y

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/gram.y,v 1.135 2009/11/12 00:13:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/gram.y,v 1.136 2009/11/13 22:43:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -256,6 +256,7 @@ static	List			*read_raise_options(void);
 %token <keyword>	K_ELSIF
 %token <keyword>	K_END
 %token <keyword>	K_ERRCODE
+%token <keyword>	K_ERROR
 %token <keyword>	K_EXCEPTION
 %token <keyword>	K_EXECUTE
 %token <keyword>	K_EXIT
@@ -301,7 +302,10 @@ static	List			*read_raise_options(void);
 %token <keyword>	K_THEN
 %token <keyword>	K_TO
 %token <keyword>	K_TYPE
+%token <keyword>	K_USE_COLUMN
+%token <keyword>	K_USE_VARIABLE
 %token <keyword>	K_USING
+%token <keyword>	K_VARIABLE_CONFLICT
 %token <keyword>	K_WARNING
 %token <keyword>	K_WHEN
 %token <keyword>	K_WHILE
@@ -322,6 +326,18 @@ comp_option		: '#' K_OPTION K_DUMP
 					{
 						plpgsql_DumpExecTree = true;
 					}
+				| '#' K_VARIABLE_CONFLICT K_ERROR
+					{
+						plpgsql_curr_compile->resolve_option = PLPGSQL_RESOLVE_ERROR;
+					}
+				| '#' K_VARIABLE_CONFLICT K_USE_VARIABLE
+					{
+						plpgsql_curr_compile->resolve_option = PLPGSQL_RESOLVE_VARIABLE;
+					}
+				| '#' K_VARIABLE_CONFLICT K_USE_COLUMN
+					{
+						plpgsql_curr_compile->resolve_option = PLPGSQL_RESOLVE_COLUMN;
+					}
 				;
 
 opt_semi		:
@@ -1969,6 +1985,7 @@ unreserved_keyword	:
 				| K_DETAIL
 				| K_DUMP
 				| K_ERRCODE
+				| K_ERROR
 				| K_FIRST
 				| K_FORWARD
 				| K_HINT
@@ -1991,6 +2008,9 @@ unreserved_keyword	:
 				| K_SCROLL
 				| K_SQLSTATE
 				| K_TYPE
+				| K_USE_COLUMN
+				| K_USE_VARIABLE
+				| K_VARIABLE_CONFLICT
 				| K_WARNING
 				;
 

src/pl/plpgsql/src/pl_comp.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_comp.c,v 1.145 2009/11/12 00:13:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_comp.c,v 1.146 2009/11/13 22:43:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -351,7 +351,7 @@ do_compile(FunctionCallInfo fcinfo,
 	function->fn_is_trigger = is_trigger;
 	function->fn_cxt = func_cxt;
 	function->out_param_varno = -1;		/* set up for no OUT param */
-	function->resolve_option = PLPGSQL_RESOLVE_BEFORE;
+	function->resolve_option = plpgsql_variable_conflict;
 
 	/*
 	 * Initialize the compiler, particularly the namespace stack.  The
@@ -782,7 +782,7 @@ plpgsql_compile_inline(char *proc_source)
 	function->fn_is_trigger = false;
 	function->fn_cxt = func_cxt;
 	function->out_param_varno = -1;		/* set up for no OUT param */
-	function->resolve_option = PLPGSQL_RESOLVE_BEFORE;
+	function->resolve_option = plpgsql_variable_conflict;
 
 	plpgsql_ns_init();
 	plpgsql_ns_push(func_name);
@@ -948,7 +948,7 @@ plpgsql_pre_column_ref(ParseState *pstate, ColumnRef *cref)
 {
 	PLpgSQL_expr *expr = (PLpgSQL_expr *) pstate->p_ref_hook_state;
 
-	if (expr->func->resolve_option == PLPGSQL_RESOLVE_BEFORE)
+	if (expr->func->resolve_option == PLPGSQL_RESOLVE_VARIABLE)
 		return resolve_column_ref(expr, cref);
 	else
 		return NULL;
@@ -963,10 +963,10 @@ plpgsql_post_column_ref(ParseState *pstate, ColumnRef *cref, Node *var)
 	PLpgSQL_expr *expr = (PLpgSQL_expr *) pstate->p_ref_hook_state;
 	Node	   *myvar;
 
-	if (expr->func->resolve_option == PLPGSQL_RESOLVE_BEFORE)
+	if (expr->func->resolve_option == PLPGSQL_RESOLVE_VARIABLE)
 		return NULL;			/* we already found there's no match */
 
-	if (expr->func->resolve_option == PLPGSQL_RESOLVE_AFTER && var != NULL)
+	if (expr->func->resolve_option == PLPGSQL_RESOLVE_COLUMN && var != NULL)
 		return NULL;			/* there's a table column, prefer that */
 
 	myvar = resolve_column_ref(expr, cref);

src/pl/plpgsql/src/pl_handler.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_handler.c,v 1.47 2009/11/04 22:26:07 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_handler.c,v 1.48 2009/11/13 22:43:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -26,6 +26,17 @@
 
 PG_MODULE_MAGIC;
 
+/* Custom GUC variable */
+static const struct config_enum_entry variable_conflict_options[] = {
+	{"error", PLPGSQL_RESOLVE_ERROR, false},
+	{"use_variable", PLPGSQL_RESOLVE_VARIABLE, false},
+	{"use_column", PLPGSQL_RESOLVE_COLUMN, false},
+	{NULL, 0, false}
+};
+
+int		plpgsql_variable_conflict = PLPGSQL_RESOLVE_ERROR;
+
+/* Hook for plugins */
 PLpgSQL_plugin **plugin_ptr = NULL;
 
 
@@ -45,6 +56,17 @@ _PG_init(void)
 
 	pg_bindtextdomain(TEXTDOMAIN);
 
+	DefineCustomEnumVariable("plpgsql.variable_conflict",
+							 gettext_noop("Sets handling of conflicts between PL/pgSQL variable names and table column names."),
+							 NULL,
+							 &plpgsql_variable_conflict,
+							 PLPGSQL_RESOLVE_ERROR,
+							 variable_conflict_options,
+							 PGC_SUSET, 0,
+							 NULL, NULL);
+
+	EmitWarningsOnPlaceholders("plpgsql");
+
 	plpgsql_HashTableInit();
 	RegisterXactCallback(plpgsql_xact_cb, NULL);
 	RegisterSubXactCallback(plpgsql_subxact_cb, NULL);

src/pl/plpgsql/src/pl_scanner.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_scanner.c,v 1.1 2009/11/12 00:13:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_scanner.c,v 1.2 2009/11/13 22:43:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -113,6 +113,7 @@ static const ScanKeyword unreserved_keywords[] = {
 	PG_KEYWORD("detail", K_DETAIL, UNRESERVED_KEYWORD)
 	PG_KEYWORD("dump", K_DUMP, UNRESERVED_KEYWORD)
 	PG_KEYWORD("errcode", K_ERRCODE, UNRESERVED_KEYWORD)
+	PG_KEYWORD("error", K_ERROR, UNRESERVED_KEYWORD)
 	PG_KEYWORD("first", K_FIRST, UNRESERVED_KEYWORD)
 	PG_KEYWORD("forward", K_FORWARD, UNRESERVED_KEYWORD)
 	PG_KEYWORD("hint", K_HINT, UNRESERVED_KEYWORD)
@@ -135,6 +136,9 @@ static const ScanKeyword unreserved_keywords[] = {
 	PG_KEYWORD("scroll", K_SCROLL, UNRESERVED_KEYWORD)
 	PG_KEYWORD("sqlstate", K_SQLSTATE, UNRESERVED_KEYWORD)
 	PG_KEYWORD("type", K_TYPE, UNRESERVED_KEYWORD)
+	PG_KEYWORD("use_column", K_USE_COLUMN, UNRESERVED_KEYWORD)
+	PG_KEYWORD("use_variable", K_USE_VARIABLE, UNRESERVED_KEYWORD)
+	PG_KEYWORD("variable_conflict", K_VARIABLE_CONFLICT, UNRESERVED_KEYWORD)
 	PG_KEYWORD("warning", K_WARNING, UNRESERVED_KEYWORD)
 };
 

src/pl/plpgsql/src/plpgsql.h

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.124 2009/11/12 00:13:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.125 2009/11/13 22:43:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -147,9 +147,9 @@ enum
  */
 typedef enum
 {
-	PLPGSQL_RESOLVE_BEFORE,		/* prefer plpgsql var to table column */
-	PLPGSQL_RESOLVE_AFTER,		/* prefer table column to plpgsql var */
-	PLPGSQL_RESOLVE_ERROR		/* throw error if ambiguous */
+	PLPGSQL_RESOLVE_ERROR,		/* throw error if ambiguous */
+	PLPGSQL_RESOLVE_VARIABLE,	/* prefer plpgsql var to table column */
+	PLPGSQL_RESOLVE_COLUMN		/* prefer table column to plpgsql var */
 } PLpgSQL_resolve_option;
 
 
@@ -794,6 +794,8 @@ typedef struct
  * Global variable declarations
  **********************************************************************/
 
+extern int	plpgsql_variable_conflict;
+
 extern bool plpgsql_check_syntax;
 extern bool plpgsql_DumpExecTree;
 extern bool plpgsql_LookupIdentifiers;

src/test/regress/expected/plpgsql.out

@@ -4004,6 +4004,7 @@ select scope_test();
 
 drop function scope_test();
 -- Check handling of conflicts between plpgsql vars and table columns.
+set plpgsql.variable_conflict = error;
 create function conflict_test() returns setof int8_tbl as $$
 declare r record;
   q1 bigint := 42;
@@ -4013,6 +4014,23 @@ begin
   end loop;
 end;
 $$ language plpgsql;
+select * from conflict_test();
+ERROR:  column reference "q1" is ambiguous
+LINE 1: select q1,q2 from int8_tbl
+               ^
+DETAIL:  It could refer to either a PL/pgSQL variable or a table column.
+QUERY:  select q1,q2 from int8_tbl
+CONTEXT:  PL/pgSQL function "conflict_test" line 4 at FOR over SELECT rows
+create or replace function conflict_test() returns setof int8_tbl as $$
+#variable_conflict use_variable
+declare r record;
+  q1 bigint := 42;
+begin
+  for r in select q1,q2 from int8_tbl loop
+    return next r;
+  end loop;
+end;
+$$ language plpgsql;
 select * from conflict_test();
  q1 |        q2         
 ----+-------------------
@@ -4023,6 +4041,26 @@ select * from conflict_test();
  42 | -4567890123456789
 (5 rows)
 
+create or replace function conflict_test() returns setof int8_tbl as $$
+#variable_conflict use_column
+declare r record;
+  q1 bigint := 42;
+begin
+  for r in select q1,q2 from int8_tbl loop
+    return next r;
+  end loop;
+end;
+$$ language plpgsql;
+select * from conflict_test();
+        q1        |        q2         
+------------------+-------------------
+              123 |               456
+              123 |  4567890123456789
+ 4567890123456789 |               123
+ 4567890123456789 |  4567890123456789
+ 4567890123456789 | -4567890123456789
+(5 rows)
+
 drop function conflict_test();
 -- Check that an unreserved keyword can be used as a variable name
 create function unreserved_test() returns int as $$

src/test/regress/sql/plpgsql.sql

@@ -3176,6 +3176,8 @@ drop function scope_test();
 
 -- Check handling of conflicts between plpgsql vars and table columns.
 
+set plpgsql.variable_conflict = error;
+
 create function conflict_test() returns setof int8_tbl as $$
 declare r record;
   q1 bigint := 42;
@@ -3188,6 +3190,32 @@ $$ language plpgsql;
 
 select * from conflict_test();
 
+create or replace function conflict_test() returns setof int8_tbl as $$
+#variable_conflict use_variable
+declare r record;
+  q1 bigint := 42;
+begin
+  for r in select q1,q2 from int8_tbl loop
+    return next r;
+  end loop;
+end;
+$$ language plpgsql;
+
+select * from conflict_test();
+
+create or replace function conflict_test() returns setof int8_tbl as $$
+#variable_conflict use_column
+declare r record;
+  q1 bigint := 42;
+begin
+  for r in select q1,q2 from int8_tbl loop
+    return next r;
+  end loop;
+end;
+$$ language plpgsql;
+
+select * from conflict_test();
+
 drop function conflict_test();
 
 -- Check that an unreserved keyword can be used as a variable name