Support this binding retrieval for backtrace frames (#4669)

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

docs/02.API-REFERENCE.md

@@ -10606,6 +10606,7 @@ main (void)
 - [jerry_backtrace_get_frame_type](#jerry_backtrace_get_frame_type)
 - [jerry_backtrace_get_location](#jerry_backtrace_get_location)
 - [jerry_backtrace_get_function](#jerry_backtrace_get_function)
+- [jerry_backtrace_get_this](#jerry_backtrace_get_this)
 - [jerry_backtrace_is_strict](#jerry_backtrace_is_strict)
 
 
@@ -10785,6 +10786,63 @@ backtrace_callback (jerry_backtrace_frame_t *frame_p,
 - [jerry_backtrace_capture](#jerry_backtrace_capture)
 
 
+## jerry_backtrace_get_this
+
+**Summary**
+
+Initialize and return with the 'this' binding private field of a backtrace frame.
+The 'this' binding is a hidden value passed to the called function. As for arrow
+functions, the 'this' binding is assigned at function creation. This getter
+function can only be called from the callback function of
+[jerry_backtrace_capture](#jerry_backtrace_capture), and the value becomes invalid
+after the callback returns.
+
+*Notes*:
+- The returned data must not be modified, and does not need to be freed.
+  Any cleanup is done automatically after the callback is returned.
+
+**Prototype**
+
+```c
+const jerry_value_t *
+jerry_backtrace_get_this (jerry_backtrace_frame_t *frame_p);
+```
+
+- `frame_p` - a frame passed to the [jerry_backtrace_callback_t](#jerry_backtrace_callback_t) callback
+- return value
+  - pointer to the 'this' binding if the binding is available,
+  - NULL otherwise
+
+*New in version [[NEXT_RELEASE]]*.
+
+**Example**
+
+See the example of [jerry_backtrace_capture](#jerry_backtrace_capture)
+with the following callback function:
+
+```c
+static bool
+backtrace_callback (jerry_backtrace_frame_t *frame_p,
+                    void *user_p)
+{
+  jerry_value_t *this_p = jerry_backtrace_get_this (frame_p);
+
+  if (this_p != NULL)
+  {
+    printf ("The 'this' binding is available");
+    return true;
+  }
+
+  printf ("The 'this' binding is NOT available");
+  return true;
+}
+```
+
+**See also**
+
+- [jerry_backtrace_capture](#jerry_backtrace_capture)
+
+
 ## jerry_backtrace_is_strict
 
 **Summary**

jerry-core/api/jerry.c

@@ -5276,6 +5276,26 @@ jerry_backtrace_get_function (jerry_backtrace_frame_t *frame_p) /**< frame point
   return NULL;
 } /* jerry_backtrace_get_function */
 
+/**
+ * Initialize and return with the 'this' binding private field of a backtrace frame.
+ * The 'this' binding is a hidden value passed to the called function. As for arrow
+ * functions, the 'this' binding is assigned at function creation.
+ *
+ * @return pointer to the 'this' binding - if the binding is available,
+ *         NULL - otherwise
+ */
+const jerry_value_t *
+jerry_backtrace_get_this (jerry_backtrace_frame_t *frame_p) /**< frame pointer */
+{
+  if (frame_p->frame_type == JERRY_BACKTRACE_FRAME_JS)
+  {
+    frame_p->this_binding = frame_p->context_p->this_binding;
+    return &frame_p->this_binding;
+  }
+
+  return NULL;
+} /* jerry_backtrace_get_this */
+
 /**
  * Returns true, if the code bound to the backtrace frame is strict mode code.
  *

jerry-core/include/jerryscript-core.h

@@ -350,6 +350,7 @@ void jerry_backtrace_capture (jerry_backtrace_callback_t callback, void *user_p)
 jerry_backtrace_frame_types_t jerry_backtrace_get_frame_type (jerry_backtrace_frame_t *frame_p);
 const jerry_backtrace_location_t *jerry_backtrace_get_location (jerry_backtrace_frame_t *frame_p);
 const jerry_value_t *jerry_backtrace_get_function (jerry_backtrace_frame_t *frame_p);
+const jerry_value_t *jerry_backtrace_get_this (jerry_backtrace_frame_t *frame_p);
 bool jerry_backtrace_is_strict (jerry_backtrace_frame_t *frame_p);
 
 /**

jerry-core/vm/vm-defines.h

@@ -157,6 +157,7 @@ struct jerry_backtrace_frame_internal_t
   uint8_t frame_type; /**< frame type */
   jerry_backtrace_location_t location; /**< location information */
   ecma_value_t function; /**< function reference */
+  ecma_value_t this_binding; /**< this binding passed to the function */
 };
 
 /**

tests/unit-core/test-backtrace.c

@@ -61,9 +61,11 @@ backtrace_callback (jerry_backtrace_frame_t *frame_p, /* frame information */
 
   const jerry_backtrace_location_t *location_p = jerry_backtrace_get_location (frame_p);
   const jerry_value_t *function_p = jerry_backtrace_get_function (frame_p);
+  const jerry_value_t *this_p = jerry_backtrace_get_this (frame_p);
 
   TEST_ASSERT (location_p != NULL);
   TEST_ASSERT (function_p != NULL);
+  TEST_ASSERT (this_p != NULL);
 
   compare_string (location_p->resource_name, "capture_test.js");
 
@@ -75,6 +77,7 @@ backtrace_callback (jerry_backtrace_frame_t *frame_p, /* frame information */
     TEST_ASSERT (location_p->line == 2);
     TEST_ASSERT (location_p->column == 1);
     TEST_ASSERT (handler_args_p[0] == *function_p);
+    TEST_ASSERT (handler_args_p[1] == *this_p);
     return true;
   }
 
@@ -83,15 +86,21 @@ backtrace_callback (jerry_backtrace_frame_t *frame_p, /* frame information */
     TEST_ASSERT (jerry_backtrace_is_strict (frame_p));
     TEST_ASSERT (location_p->line == 7);
     TEST_ASSERT (location_p->column == 1);
-    TEST_ASSERT (handler_args_p[1] == *function_p);
+    TEST_ASSERT (handler_args_p[2] == *function_p);
+    TEST_ASSERT (jerry_value_is_undefined (*this_p));
     return true;
   }
 
+  jerry_value_t global = jerry_get_global_object ();
+
   TEST_ASSERT (frame_index == 3);
   TEST_ASSERT (!jerry_backtrace_is_strict (frame_p));
   TEST_ASSERT (location_p->line == 11);
   TEST_ASSERT (location_p->column == 1);
-  TEST_ASSERT (handler_args_p[2] == *function_p);
+  TEST_ASSERT (handler_args_p[3] == *function_p);
+  TEST_ASSERT (global == *this_p);
+
+  jerry_release_value (global);
   return false;
 } /* backtrace_callback */
 
@@ -170,7 +179,7 @@ capture_handler (const jerry_call_info_t *call_info_p, /**< call information */
   JERRY_UNUSED (args_p);
   JERRY_UNUSED (args_count);
 
-  TEST_ASSERT (args_count == 0 || args_count == 2 || args_count == 3);
+  TEST_ASSERT (args_count == 0 || args_count == 2 || args_count == 4);
   TEST_ASSERT (args_count == 0 || frame_index == 0);
 
   jerry_backtrace_callback_t callback = backtrace_callback;
@@ -187,7 +196,7 @@ capture_handler (const jerry_call_info_t *call_info_p, /**< call information */
   handler_args_p = args_p;
   jerry_backtrace_capture (callback, (void *) args_p);
 
-  TEST_ASSERT (args_count == 0 || frame_index == (int) args_count);
+  TEST_ASSERT (args_count == 0 || frame_index == (args_count == 4 ? 3 : 2));
 
   return jerry_create_undefined ();
 } /* capture_handler */
@@ -323,13 +332,13 @@ test_get_backtrace_api_call (void)
   /* Test frame capturing. */
 
   frame_index = 0;
-  source_p = ("function f() {\n"
-              "  return capture(f, g, h);\n"
-              "}\n"
+  source_p = ("var o = { f:function() {\n"
+              "  return capture(o.f, o, g, h);\n"
+              "} }\n"
               "\n"
               "function g() {\n"
               "  'use strict';\n"
-              "  return f();\n"
+              "  return o.f();\n"
               "}\n"
               "\n"
               "function h() {\n"