Add backtrace print when the 'assert' js method fails

In the jerry-ext there is a native 'assert' handler implemented.
This change adds extra backtrace information if an 'assert' call fails.

To print out the backtrace the library should be built with `JERRY_LINE_INFO` enabled.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.u-szeged@partner.samsung.com

Author: galpeter

docs/10.EXT-REFERENCE-HANDLER.md

@@ -421,6 +421,9 @@ For example usage see [jerryx_set_properties](#jerryx_set_properties).
 
 Hard assert for scripts. The routine calls `jerry_port_fatal` on assertion failure.
 
+If the `JERRY_FEATURE_LINE_INFO` runtime feature is enabled (build option: `JERRY_LINE_INFO`)
+a backtrace is also printed out.
+
 **Prototype**
 
 ```c

jerry-ext/handler/handler-assert.c

@@ -16,9 +16,15 @@
 #include "jerryscript-ext/handler.h"
 #include "jerryscript-port.h"
 
+#include <inttypes.h>
+
 /**
  * Hard assert for scripts. The routine calls jerry_port_fatal on assertion failure.
  *
+ * Notes:
+ *  * If the `JERRY_FEATURE_LINE_INFO` runtime feature is enabled (build option: `JERRY_LINE_INFO`)
+ *    a backtrace is also printed out.
+ *
  * @return true - if only one argument was passed and that argument was a boolean true.
  *         Note that the function does not return otherwise.
  */
@@ -38,7 +44,52 @@ jerryx_handler_assert_fatal (const jerry_value_t func_obj_val, /**< function obj
     return jerry_create_boolean (true);
   }
 
+  /* Assert failed, print a bit of JS backtrace */
   jerry_port_log (JERRY_LOG_LEVEL_ERROR, "Script Error: assertion failed\n");
+
+  if (jerry_is_feature_enabled (JERRY_FEATURE_LINE_INFO))
+  {
+    jerry_port_log (JERRY_LOG_LEVEL_ERROR, "Script backtrace (top 5):\n");
+
+    /* If the line info feature is disabled an empty array will be returned. */
+    jerry_value_t backtrace_array = jerry_get_backtrace (5);
+    uint32_t array_length = jerry_get_array_length (backtrace_array);
+
+    for (uint32_t idx = 0; idx < array_length; idx++)
+    {
+      jerry_value_t property = jerry_get_property_by_index (backtrace_array, idx);
+
+      jerry_length_t total_size = jerry_get_utf8_string_size (property);
+      jerry_length_t current_size = 0;
+      jerry_char_t string_buffer[64];
+      const jerry_length_t copy_size = (jerry_length_t) (sizeof (string_buffer) - 1);
+
+      /* On some systems the uint32_t values can't be printed with "%u" and
+       * on some systems it can be printed. To avoid differences in the uint32_t typdef
+       * The "PRIu32" macro is used to correctly add the formatter.
+       */
+      jerry_port_log (JERRY_LOG_LEVEL_ERROR, " %"PRIu32": ", idx);
+      do
+      {
+        jerry_size_t copied_bytes = jerry_substring_to_utf8_char_buffer (property,
+                                                                         current_size,
+                                                                         current_size + copy_size,
+                                                                         string_buffer,
+                                                                         copy_size);
+        string_buffer[copied_bytes] = '\0';
+        jerry_port_log (JERRY_LOG_LEVEL_ERROR, "%s", string_buffer);
+
+        current_size += copied_bytes;
+      }
+      while (total_size != current_size);
+      jerry_port_log (JERRY_LOG_LEVEL_ERROR, "\n");
+
+      jerry_release_value (property);
+    }
+
+    jerry_release_value (backtrace_array);
+  }
+
   jerry_port_fatal (ERR_FAILED_INTERNAL_ASSERTION);
 } /* jerryx_handler_assert_fatal */