Fix core dump in jsonb #> operator, and add regression test cases.

jsonb's #> operator segfaulted (dereferencing a null pointer) if the RHS
was a zero-length array, as reported in bug #11207 from Justin Van Winkle.
json's #> operator returns NULL in such cases, so for the moment let's
make jsonb act likewise.

Also add a bunch of regression test queries memorializing the -> and #>
operators' behavior for this and other corner cases.

There is a good argument for changing some of these behaviors, as they
are not very consistent with each other, and throwing an error isn't
necessarily a desirable behavior for operators that are likely to be
used in indexes.  However, everybody can agree that a core dump is the
Wrong Thing, and we need test cases even if we decide to change their
expected output later.

1 files changed, 15 insertions, 1 deletions

diff --git a/src/backend/utils/adt/jsonfuncs.c b/src/backend/utils/adt/jsonfuncs.c
index 6c16a953dd3..5fabef0de96 100644
--- a/src/backend/utils/adt/jsonfuncs.c
+++ b/src/backend/utils/adt/jsonfuncs.c
@@ -726,6 +726,13 @@ get_path_all(FunctionCallInfo fcinfo, const char *funcname, bool as_text)
 	deconstruct_array(path, TEXTOID, -1, false, 'i',
 					  &pathtext, &pathnulls, &npath);
 
+	/*
+	 * If the array is empty, return NULL; this is dubious but it's what 9.3
+	 * did.
+	 */
+	if (npath <= 0)
+		PG_RETURN_NULL();
+
 	tpath = palloc(npath * sizeof(char *));
 	ipath = palloc(npath * sizeof(int));
 
@@ -1100,11 +1107,11 @@ get_jsonb_path_all(FunctionCallInfo fcinfo, const char *funcname, bool as_text)
 {
 	Jsonb	   *jb = PG_GETARG_JSONB(0);
 	ArrayType  *path = PG_GETARG_ARRAYTYPE_P(1);
+	Jsonb	   *res;
 	Datum	   *pathtext;
 	bool	   *pathnulls;
 	int			npath;
 	int			i;
-	Jsonb	   *res;
 	bool		have_object = false,
 				have_array = false;
 	JsonbValue *jbvp = NULL;
@@ -1120,6 +1127,13 @@ get_jsonb_path_all(FunctionCallInfo fcinfo, const char *funcname, bool as_text)
 	deconstruct_array(path, TEXTOID, -1, false, 'i',
 					  &pathtext, &pathnulls, &npath);
 
+	/*
+	 * If the array is empty, return NULL; this is dubious but it's what 9.3
+	 * did.
+	 */
+	if (npath <= 0)
+		PG_RETURN_NULL();
+
 	if (JB_ROOT_IS_OBJECT(jb))
 		have_object = true;
 	else if (JB_ROOT_IS_ARRAY(jb) && !JB_ROOT_IS_SCALAR(jb))