jinja : fix negative step slice with start/stop values (#24580)

diff --git a/common/jinja/runtime.cpp b/common/jinja/runtime.cpp
index f81d98d954a1dc0608aa18421a29a83ec3f7378b..8d8d80b22ce6a0e85709e3f0b8e526f99d1b8c4a 100644 (file)
--- a/common/jinja/runtime.cpp
+++ b/common/jinja/runtime.cpp
@@ -761,9 +761,9 @@ value member_expression::execute_impl(context & ctx) {
 
         if (is_stmt<slice_expression>(this->property)) {
             auto s = cast_stmt<slice_expression>(this->property);
-            value start_val = s->start_expr ? s->start_expr->execute(ctx) : mk_val<value_int>(0);
-            value stop_val  = s->stop_expr  ? s->stop_expr->execute(ctx)  : mk_val<value_int>(arr_size);
             value step_val  = s->step_expr  ? s->step_expr->execute(ctx)  : mk_val<value_int>(1);
+            value start_val = s->start_expr ? s->start_expr->execute(ctx) : (step_val->as_int() < 0 ? mk_val<value_int>(arr_size - 1) : mk_val<value_int>(0));
+            value stop_val  = s->stop_expr  ? s->stop_expr->execute(ctx)  : (step_val->as_int() < 0 ? mk_val<value_int>(-1) : mk_val<value_int>(arr_size));
 
             // translate to function call: obj.slice(start, stop, step)
             JJ_DEBUG("Member expression is a slice: start %s, stop %s, step %s",

diff --git a/common/jinja/value.cpp b/common/jinja/value.cpp
index 72a12f665cfc364d5fab164739c03eb68dfcceb1..cd6a36956ceadede4bf44fc2e52b94cb62f01045 100644 (file)
--- a/common/jinja/value.cpp
+++ b/common/jinja/value.cpp
@@ -90,14 +90,14 @@ static T slice(const T & array, int64_t start, int64_t stop, int64_t step = 1) {
             stop_val = std::min(stop_val, len);
         }
     } else {
-        start_val = len - 1;
+        start_val = start;
         if (start_val < 0) {
-            start_val = std::max(len + start_val, (int64_t)-1);
+            start_val = std::max(len + start_val, (int64_t)0);
         } else {
             start_val = std::min(start_val, len - 1);
         }
 
-        stop_val = -1;
+        stop_val = stop;
         if (stop_val < -1) {
             stop_val = std::max(len + stop_val, (int64_t)-1);
         } else {

diff --git a/tests/test-jinja.cpp b/tests/test-jinja.cpp
index 21250d04c69f027fe64d66152cdd801d49761a3f..7bf6791b0a652c2a4e4505ea4811646da8cfedc9 100644 (file)
--- a/tests/test-jinja.cpp
+++ b/tests/test-jinja.cpp
@@ -435,6 +435,24 @@ static void test_expressions(testing & t) {
         "('c', 'b', 'a')"
     );
 
+    test_template(t, "string slice negative step",
+        "{{ 'abcdef'[::-2] }}",
+        json::object(),
+        "fdb"
+    );
+
+    test_template(t, "string slice negative start and step",
+        "{{ 'abcdef'[-1:1:-1] }}",
+        json::object(),
+        "fedc"
+    );
+
+    test_template(t, "string slice negative start, stop and step",
+        "{{ 'abcdef'[-1:-5:-1] }}",
+        json::object(),
+        "fedc"
+    );
+
     test_template(t, "arithmetic",
         "{{ (a + b) * c }}",
         {{"a", 2}, {"b", 3}, {"c", 4}},