Fix plpgsql to reinitialize record variables at block re-entry.

If one exits and re-enters a DECLARE ... BEGIN ... END block within a
single execution of a plpgsql function, perhaps due to a surrounding loop,
the declared variables are supposed to get re-initialized to null (or
whatever their initializer is).  But this failed to happen for variables
of type "record", because while exec_stmt_block() expected such variables
to be included in the block's initvarnos list, plpgsql_add_initdatums()
only adds DTYPE_VAR variables to that list.  This bug appears to have
been there since the aboriginal addition of plpgsql to our tree.

Fix by teaching plpgsql_add_initdatums() to include DTYPE_REC variables
as well.  (We don't need to consider other DTYPEs because they don't
represent separately-stored values.)  I failed to resist the temptation
to make some nearby cosmetic adjustments, too.

No back-patch, because there have not been field complaints, and it
seems possible that somewhere out there someone has code depending
on the incorrect behavior.  In any case this change would have no
impact on correctly-written code.

Discussion: https://postgr.es/m/22994.1512800671@sss.pgh.pa.us

src/pl/plpgsql/src/pl_comp.c

@@ -2384,14 +2384,14 @@ plpgsql_finish_datums(PLpgSQL_function *function)
 
 /* ----------
  * plpgsql_add_initdatums		Make an array of the datum numbers of
- *					all the simple VAR datums created since the last call
+ *					all the initializable datums created since the last call
  *					to this function.
  *
  * If varnos is NULL, we just forget any datum entries created since the
  * last call.
  *
- * This is used around a DECLARE section to create a list of the VARs
- * that have to be initialized at block entry.  Note that VARs can also
+ * This is used around a DECLARE section to create a list of the datums
+ * that have to be initialized at block entry.  Note that datums can also
  * be created elsewhere than DECLARE, eg by a FOR-loop, but it is then
  * the responsibility of special-purpose code to initialize them.
  * ----------
@@ -2402,11 +2402,16 @@ plpgsql_add_initdatums(int **varnos)
 	int			i;
 	int			n = 0;
 
+	/*
+	 * The set of dtypes recognized here must match what exec_stmt_block()
+	 * cares about (re)initializing at block entry.
+	 */
 	for (i = datums_last; i < plpgsql_nDatums; i++)
 	{
 		switch (plpgsql_Datums[i]->dtype)
 		{
 			case PLPGSQL_DTYPE_VAR:
+			case PLPGSQL_DTYPE_REC:
 				n++;
 				break;
 
@@ -2427,6 +2432,7 @@ plpgsql_add_initdatums(int **varnos)
 				switch (plpgsql_Datums[i]->dtype)
 				{
 					case PLPGSQL_DTYPE_VAR:
+					case PLPGSQL_DTYPE_REC:
 						(*varnos)[n++] = plpgsql_Datums[i]->dno;
 
 					default:

src/pl/plpgsql/src/pl_exec.c

@@ -1184,7 +1184,6 @@ exec_stmt_block(PLpgSQL_execstate *estate, PLpgSQL_stmt_block *block)
 {
 	volatile int rc = -1;
 	int			i;
-	int			n;
 
 	/*
 	 * First initialize all variables declared in this block
@@ -1193,13 +1192,17 @@ exec_stmt_block(PLpgSQL_execstate *estate, PLpgSQL_stmt_block *block)
 
 	for (i = 0; i < block->n_initvars; i++)
 	{
-		n = block->initvarnos[i];
+		int			n = block->initvarnos[i];
+		PLpgSQL_datum *datum = estate->datums[n];
 
-		switch (estate->datums[n]->dtype)
+		/*
+		 * The set of dtypes handled here must match plpgsql_add_initdatums().
+		 */
+		switch (datum->dtype)
 		{
 			case PLPGSQL_DTYPE_VAR:
 				{
-					PLpgSQL_var *var = (PLpgSQL_var *) (estate->datums[n]);
+					PLpgSQL_var *var = (PLpgSQL_var *) datum;
 
 					/*
 					 * Free any old value, in case re-entering block, and
@@ -1241,7 +1244,7 @@ exec_stmt_block(PLpgSQL_execstate *estate, PLpgSQL_stmt_block *block)
 
 			case PLPGSQL_DTYPE_REC:
 				{
-					PLpgSQL_rec *rec = (PLpgSQL_rec *) (estate->datums[n]);
+					PLpgSQL_rec *rec = (PLpgSQL_rec *) datum;
 
 					if (rec->freetup)
 					{
@@ -1258,13 +1261,8 @@ exec_stmt_block(PLpgSQL_execstate *estate, PLpgSQL_stmt_block *block)
 				}
 				break;
 
-			case PLPGSQL_DTYPE_RECFIELD:
-			case PLPGSQL_DTYPE_ARRAYELEM:
-				break;
-
 			default:
-				elog(ERROR, "unrecognized dtype: %d",
-					 estate->datums[n]->dtype);
+				elog(ERROR, "unrecognized dtype: %d", datum->dtype);
 		}
 	}
 

src/pl/plpgsql/src/plpgsql.h

@@ -407,8 +407,8 @@ typedef struct PLpgSQL_stmt_block
 	int			lineno;
 	char	   *label;
 	List	   *body;			/* List of statements */
-	int			n_initvars;
-	int		   *initvarnos;
+	int			n_initvars;		/* Length of initvarnos[] */
+	int		   *initvarnos;		/* dnos of variables declared in this block */
 	PLpgSQL_exception_block *exceptions;
 } PLpgSQL_stmt_block;
 

src/test/regress/expected/plpgsql.out

@@ -5025,6 +5025,33 @@ select scope_test();
 (1 row)
 
 drop function scope_test();
+-- Check that variables are reinitialized on block re-entry.
+do $$
+begin
+  for i in 1..3 loop
+    declare
+      x int;
+      y int := i;
+      r record;
+    begin
+      if i = 1 then
+        x := 42;
+        r := row(i, i+1);
+      end if;
+      raise notice 'x = %', x;
+      raise notice 'y = %', y;
+      raise notice 'r = %', r;
+    end;
+  end loop;
+end$$;
+NOTICE:  x = 42
+NOTICE:  y = 1
+NOTICE:  r = (1,2)
+NOTICE:  x = <NULL>
+NOTICE:  y = 2
+ERROR:  record "r" is not assigned yet
+DETAIL:  The tuple structure of a not-yet-assigned record is indeterminate.
+CONTEXT:  PL/pgSQL function inline_code_block line 15 at RAISE
 -- Check handling of conflicts between plpgsql vars and table columns.
 set plpgsql.variable_conflict = error;
 create function conflict_test() returns setof int8_tbl as $$

src/test/regress/sql/plpgsql.sql

@@ -4014,6 +4014,27 @@ select scope_test();
 
 drop function scope_test();
 
+-- Check that variables are reinitialized on block re-entry.
+
+do $$
+begin
+  for i in 1..3 loop
+    declare
+      x int;
+      y int := i;
+      r record;
+    begin
+      if i = 1 then
+        x := 42;
+        r := row(i, i+1);
+      end if;
+      raise notice 'x = %', x;
+      raise notice 'y = %', y;
+      raise notice 'r = %', r;
+    end;
+  end loop;
+end$$;
+
 -- Check handling of conflicts between plpgsql vars and table columns.
 
 set plpgsql.variable_conflict = error;