Extra warnings and errors for PL/pgSQL

Infrastructure to allow
 plpgsql.extra_warnings
 plpgsql.extra_errors

Initial extra checks only for shadowed_variables

Marko Tiikkaja and Petr Jelinek
Reviewed by Simon Riggs and Pavel Stěhule

doc/src/sgml/plpgsql.sgml

@@ -4710,6 +4710,56 @@ a_output := a_output || $$ if v_$$ || referrer_keys.kind || $$ like '$$
    </varlistentry>
   </variablelist>
 
+  </sect2>
+  <sect2 id="plpgsql-extra-checks">
+   <title>Additional compile-time checks</title>
+
+   <para>
+    To aid the user in finding instances of simple but common problems before
+    they cause harm, <application>PL/PgSQL</> provides additional
+    <replaceable>checks</>. When enabled, depending on the configuration, they
+    can be used to emit either a <literal>WARNING</> or an <literal>ERROR</>
+    during the compilation of a function. A function which has received
+    a <literal>WARNING</> can be executed without producing further messages,
+    so you are advised to test in a separate development environment.
+   </para>
+
+ <para>
+  These additional checks are enabled through the configuration variables
+  <varname>plpgsql.extra_warnings</> for warnings and 
+  <varname>plpgsql.extra_errors</> for errors. Both can be set either to
+  a comma-separated list of checks, <literal>"none"</> or <literal>"all"</>.
+  The default is <literal>"none"</>. Currently the list of available checks
+  includes only one:
+  <variablelist>
+   <varlistentry>
+    <term><varname>shadowed_variables</varname></term>
+    <listitem>
+     <para>
+      Checks if a declaration shadows a previously defined variable. 
+     </para>
+    </listitem>
+   </varlistentry>
+  </variablelist>
+
+  The following example shows the effect of <varname>plpgsql.extra_warnings</>
+  set to <varname>shadowed_variables</>:
+<programlisting>
+SET plpgsql.extra_warnings TO 'shadowed_variables';
+
+CREATE FUNCTION foo(f1 int) RETURNS int AS $$
+DECLARE
+f1 int;
+BEGIN
+RETURN f1;
+END
+$$ LANGUAGE plpgsql;
+WARNING:  variable "f1" shadows a previously defined variable
+LINE 3: f1 int;
+        ^
+CREATE FUNCTION
+</programlisting>
+ </para>
  </sect2>
  </sect1>
 

src/pl/plpgsql/src/pl_comp.c

@@ -352,6 +352,9 @@ do_compile(FunctionCallInfo fcinfo,
 	function->out_param_varno = -1;		/* set up for no OUT param */
 	function->resolve_option = plpgsql_variable_conflict;
 	function->print_strict_params = plpgsql_print_strict_params;
+	/* only promote extra warnings and errors at CREATE FUNCTION time */
+	function->extra_warnings = forValidator ? plpgsql_extra_warnings : 0;
+	function->extra_errors = forValidator ? plpgsql_extra_errors : 0;
 
 	if (is_dml_trigger)
 		function->fn_is_trigger = PLPGSQL_DML_TRIGGER;
@@ -849,6 +852,9 @@ plpgsql_compile_inline(char *proc_source)
 	function->out_param_varno = -1;		/* set up for no OUT param */
 	function->resolve_option = plpgsql_variable_conflict;
 	function->print_strict_params = plpgsql_print_strict_params;
+	/* don't do extra validation for inline code as we don't want to add spam at runtime */
+	function->extra_warnings = 0;
+	function->extra_errors = 0;
 
 	plpgsql_ns_init();
 	plpgsql_ns_push(func_name);

src/pl/plpgsql/src/pl_gram.y

@@ -727,6 +727,21 @@ decl_varname	: T_WORD
 											  $1.ident, NULL, NULL,
 											  NULL) != NULL)
 							yyerror("duplicate declaration");
+
+						if (plpgsql_curr_compile->extra_warnings & PLPGSQL_XCHECK_SHADOWVAR ||
+							plpgsql_curr_compile->extra_errors & PLPGSQL_XCHECK_SHADOWVAR)
+						{
+							PLpgSQL_nsitem *nsi;
+							nsi = plpgsql_ns_lookup(plpgsql_ns_top(), false,
+													$1.ident, NULL, NULL, NULL);
+							if (nsi != NULL)
+								ereport(plpgsql_curr_compile->extra_errors & PLPGSQL_XCHECK_SHADOWVAR ? ERROR : WARNING,
+										(errcode(ERRCODE_DUPLICATE_ALIAS),
+										 errmsg("variable \"%s\" shadows a previously defined variable",
+												$1.ident),
+										 parser_errposition(@1)));
+						}
+
 					}
 				| unreserved_keyword
 					{
@@ -740,6 +755,21 @@ decl_varname	: T_WORD
 											  $1, NULL, NULL,
 											  NULL) != NULL)
 							yyerror("duplicate declaration");
+
+						if (plpgsql_curr_compile->extra_warnings & PLPGSQL_XCHECK_SHADOWVAR ||
+							plpgsql_curr_compile->extra_errors & PLPGSQL_XCHECK_SHADOWVAR)
+						{
+							PLpgSQL_nsitem *nsi;
+							nsi = plpgsql_ns_lookup(plpgsql_ns_top(), false,
+													$1, NULL, NULL, NULL);
+							if (nsi != NULL)
+								ereport(plpgsql_curr_compile->extra_errors & PLPGSQL_XCHECK_SHADOWVAR ? ERROR : WARNING,
+										(errcode(ERRCODE_DUPLICATE_ALIAS),
+										 errmsg("variable \"%s\" shadows a previously defined variable",
+												$1),
+										 parser_errposition(@1)));
+						}
+
 					}
 				;
 

src/pl/plpgsql/src/pl_handler.c

@@ -25,6 +25,11 @@
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 
+
+static bool plpgsql_extra_checks_check_hook(char **newvalue, void **extra, GucSource source);
+static void plpgsql_extra_warnings_assign_hook(const char *newvalue, void *extra);
+static void plpgsql_extra_errors_assign_hook(const char *newvalue, void *extra);
+
 PG_MODULE_MAGIC;
 
 /* Custom GUC variable */
@@ -39,10 +44,89 @@ int			plpgsql_variable_conflict = PLPGSQL_RESOLVE_ERROR;
 
 bool		plpgsql_print_strict_params = false;
 
+char		*plpgsql_extra_warnings_string = NULL;
+char		*plpgsql_extra_errors_string = NULL;
+int			plpgsql_extra_warnings;
+int			plpgsql_extra_errors;
+
 /* Hook for plugins */
 PLpgSQL_plugin **plugin_ptr = NULL;
 
 
+static bool
+plpgsql_extra_checks_check_hook(char **newvalue, void **extra, GucSource source)
+{
+	char	   *rawstring;
+	List	   *elemlist;
+	ListCell   *l;
+	int		    extrachecks = 0;
+	int		   *myextra;
+
+	if (pg_strcasecmp(*newvalue, "all") == 0)
+		extrachecks = PLPGSQL_XCHECK_ALL;
+	else if (pg_strcasecmp(*newvalue, "none") == 0)
+		extrachecks = PLPGSQL_XCHECK_NONE;
+	else
+	{
+		/* Need a modifiable copy of string */
+		rawstring = pstrdup(*newvalue);
+
+		/* Parse string into list of identifiers */
+		if (!SplitIdentifierString(rawstring, ',', &elemlist))
+		{
+			/* syntax error in list */
+			GUC_check_errdetail("List syntax is invalid.");
+			pfree(rawstring);
+			list_free(elemlist);
+			return false;
+		}
+
+		foreach(l, elemlist)
+		{
+			char	   *tok = (char *) lfirst(l);
+
+			if (pg_strcasecmp(tok, "shadowed_variables") == 0)
+				extrachecks |= PLPGSQL_XCHECK_SHADOWVAR;
+			else if (pg_strcasecmp(tok, "all") == 0 || pg_strcasecmp(tok, "none") == 0)
+			{
+				GUC_check_errdetail("Key word \"%s\" cannot be combined with other key words.", tok);
+				pfree(rawstring);
+				list_free(elemlist);
+				return false;
+			}
+			else
+			{
+				GUC_check_errdetail("Unrecognized key word: \"%s\".", tok);
+				pfree(rawstring);
+				list_free(elemlist);
+				return false;
+			}
+		}
+
+		pfree(rawstring);
+		list_free(elemlist);
+	}
+
+	myextra = (int *) malloc(sizeof(int));
+	*myextra = extrachecks;
+	*extra = (void *) myextra;
+
+	return true;
+}
+
+static void
+plpgsql_extra_warnings_assign_hook(const char *newvalue, void *extra)
+{
+	plpgsql_extra_warnings = *((int *) extra);
+}
+
+static void
+plpgsql_extra_errors_assign_hook(const char *newvalue, void *extra)
+{
+	plpgsql_extra_errors = *((int *) extra);
+}
+
+
 /*
  * _PG_init()			- library load-time initialization
  *
@@ -76,6 +160,26 @@ _PG_init(void)
 							 PGC_USERSET, 0,
 							 NULL, NULL, NULL);
 
+	DefineCustomStringVariable("plpgsql.extra_warnings",
+							   gettext_noop("List of programming constructs which should produce a warning."),
+							   NULL,
+							   &plpgsql_extra_warnings_string,
+							   "none",
+							   PGC_USERSET, GUC_LIST_INPUT,
+							   plpgsql_extra_checks_check_hook,
+							   plpgsql_extra_warnings_assign_hook,
+							   NULL);
+
+	DefineCustomStringVariable("plpgsql.extra_errors",
+							   gettext_noop("List of programming constructs which should produce an error."),
+							   NULL,
+							   &plpgsql_extra_errors_string,
+							   "none",
+							   PGC_USERSET, GUC_LIST_INPUT,
+							   plpgsql_extra_checks_check_hook,
+							   plpgsql_extra_errors_assign_hook,
+							   NULL);
+
 	EmitWarningsOnPlaceholders("plpgsql");
 
 	plpgsql_HashTableInit();

src/pl/plpgsql/src/plpgsql.h

@@ -739,6 +739,10 @@ typedef struct PLpgSQL_function
 
 	bool		print_strict_params;
 
+	/* extra checks */
+	int 		extra_warnings;
+	int 		extra_errors;
+
 	int			ndatums;
 	PLpgSQL_datum **datums;
 	PLpgSQL_stmt_block *action;
@@ -881,6 +885,14 @@ extern int	plpgsql_variable_conflict;
 
 extern bool plpgsql_print_strict_params;
 
+/* extra compile-time checks */
+#define PLPGSQL_XCHECK_NONE			0
+#define PLPGSQL_XCHECK_SHADOWVAR	1
+#define PLPGSQL_XCHECK_ALL			((int) ~0)
+
+extern int plpgsql_extra_warnings;
+extern int plpgsql_extra_errors;
+
 extern bool plpgsql_check_syntax;
 extern bool plpgsql_DumpExecTree;
 

src/test/regress/expected/plpgsql.out

@@ -3208,6 +3208,128 @@ select footest();
 ERROR:  query returned more than one row
 DETAIL:  parameters: p1 = '2', p3 = 'foo'
 CONTEXT:  PL/pgSQL function footest() line 10 at SQL statement
+-- test warnings and errors
+set plpgsql.extra_warnings to 'all';
+set plpgsql.extra_warnings to 'none';
+set plpgsql.extra_errors to 'all';
+set plpgsql.extra_errors to 'none';
+-- test warnings when shadowing a variable
+set plpgsql.extra_warnings to 'shadowed_variables';
+-- simple shadowing of input and output parameters
+create or replace function shadowtest(in1 int)
+	returns table (out1 int) as $$
+declare
+in1 int;
+out1 int;
+begin
+end
+$$ language plpgsql;
+WARNING:  variable "in1" shadows a previously defined variable
+LINE 4: in1 int;
+        ^
+WARNING:  variable "out1" shadows a previously defined variable
+LINE 5: out1 int;
+        ^
+select shadowtest(1);
+ shadowtest 
+------------
+(0 rows)
+
+set plpgsql.extra_warnings to 'shadowed_variables';
+select shadowtest(1);
+ shadowtest 
+------------
+(0 rows)
+
+create or replace function shadowtest(in1 int)
+	returns table (out1 int) as $$
+declare
+in1 int;
+out1 int;
+begin
+end
+$$ language plpgsql;
+WARNING:  variable "in1" shadows a previously defined variable
+LINE 4: in1 int;
+        ^
+WARNING:  variable "out1" shadows a previously defined variable
+LINE 5: out1 int;
+        ^
+select shadowtest(1);
+ shadowtest 
+------------
+(0 rows)
+
+drop function shadowtest(int);
+-- shadowing in a second DECLARE block
+create or replace function shadowtest()
+	returns void as $$
+declare
+f1 int;
+begin
+	declare
+	f1 int;
+	begin
+	end;
+end$$ language plpgsql;
+WARNING:  variable "f1" shadows a previously defined variable
+LINE 7:  f1 int;
+         ^
+drop function shadowtest();
+-- several levels of shadowing
+create or replace function shadowtest(in1 int)
+	returns void as $$
+declare
+in1 int;
+begin
+	declare
+	in1 int;
+	begin
+	end;
+end$$ language plpgsql;
+WARNING:  variable "in1" shadows a previously defined variable
+LINE 4: in1 int;
+        ^
+WARNING:  variable "in1" shadows a previously defined variable
+LINE 7:  in1 int;
+         ^
+drop function shadowtest(int);
+-- shadowing in cursor definitions
+create or replace function shadowtest()
+	returns void as $$
+declare
+f1 int;
+c1 cursor (f1 int) for select 1;
+begin
+end$$ language plpgsql;
+WARNING:  variable "f1" shadows a previously defined variable
+LINE 5: c1 cursor (f1 int) for select 1;
+                   ^
+drop function shadowtest();
+-- test errors when shadowing a variable
+set plpgsql.extra_errors to 'shadowed_variables';
+create or replace function shadowtest(f1 int)
+	returns boolean as $$
+declare f1 int; begin return 1; end $$ language plpgsql;
+ERROR:  variable "f1" shadows a previously defined variable
+LINE 3: declare f1 int; begin return 1; end $$ language plpgsql;
+                ^
+select shadowtest(1);
+ERROR:  function shadowtest(integer) does not exist
+LINE 1: select shadowtest(1);
+               ^
+HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
+reset plpgsql.extra_errors;
+reset plpgsql.extra_warnings;
+create or replace function shadowtest(f1 int)
+	returns boolean as $$
+declare f1 int; begin return 1; end $$ language plpgsql;
+select shadowtest(1);
+ shadowtest 
+------------
+ t
+(1 row)
+
 -- test scrollable cursor support
 create function sc_test() returns setof integer as $$
 declare

src/test/regress/sql/plpgsql.sql

@@ -2689,6 +2689,95 @@ end$$ language plpgsql;
 
 select footest();
 
+-- test warnings and errors
+set plpgsql.extra_warnings to 'all';
+set plpgsql.extra_warnings to 'none';
+set plpgsql.extra_errors to 'all';
+set plpgsql.extra_errors to 'none';
+
+-- test warnings when shadowing a variable
+
+set plpgsql.extra_warnings to 'shadowed_variables';
+
+-- simple shadowing of input and output parameters
+create or replace function shadowtest(in1 int)
+	returns table (out1 int) as $$
+declare
+in1 int;
+out1 int;
+begin
+end
+$$ language plpgsql;
+select shadowtest(1);
+
+set plpgsql.extra_warnings to 'shadowed_variables';
+select shadowtest(1);
+create or replace function shadowtest(in1 int)
+	returns table (out1 int) as $$
+declare
+in1 int;
+out1 int;
+begin
+end
+$$ language plpgsql;
+select shadowtest(1);
+drop function shadowtest(int);
+
+-- shadowing in a second DECLARE block
+create or replace function shadowtest()
+	returns void as $$
+declare
+f1 int;
+begin
+	declare
+	f1 int;
+	begin
+	end;
+end$$ language plpgsql;
+drop function shadowtest();
+
+-- several levels of shadowing
+create or replace function shadowtest(in1 int)
+	returns void as $$
+declare
+in1 int;
+begin
+	declare
+	in1 int;
+	begin
+	end;
+end$$ language plpgsql;
+drop function shadowtest(int);
+
+-- shadowing in cursor definitions
+create or replace function shadowtest()
+	returns void as $$
+declare
+f1 int;
+c1 cursor (f1 int) for select 1;
+begin
+end$$ language plpgsql;
+drop function shadowtest();
+
+-- test errors when shadowing a variable
+
+set plpgsql.extra_errors to 'shadowed_variables';
+
+create or replace function shadowtest(f1 int)
+	returns boolean as $$
+declare f1 int; begin return 1; end $$ language plpgsql;
+
+select shadowtest(1);
+
+reset plpgsql.extra_errors;
+reset plpgsql.extra_warnings;
+
+create or replace function shadowtest(f1 int)
+	returns boolean as $$
+declare f1 int; begin return 1; end $$ language plpgsql;
+
+select shadowtest(1);
+
 -- test scrollable cursor support
 
 create function sc_test() returns setof integer as $$