lexical this

mcode.cm

@@ -2767,6 +2767,7 @@ var mcode = function(ast) {
     var result = null
     var saved_label = 0
     var saved_func = 0
+    var captured_this = 0
 
     push(parent_states, saved)
 
@@ -2818,6 +2819,13 @@ var mcode = function(ast) {
       s_max_slot = s_next_temp_slot
     }
 
+    // Arrow functions capture the enclosing this via closure
+    if (is_arrow) {
+      captured_this = alloc_slot()
+      emit_3("get", captured_this, saved.this_slot, 1)
+      s_this_slot = captured_this
+    }
+
     // Default parameter initialization
     ps = 1
     _i = 0

tests/suite.cm

@@ -3498,4 +3498,59 @@ return {
         }
     },
 
+    // ============================================================================
+    // ARROW FUNCTION LEXICAL THIS
+    // ============================================================================
+
+    test_arrow_captures_this: function() {
+        var obj = {
+            value: 42,
+            getIt: function() {
+                var arrow = () => this.value
+                return arrow()
+            }
+        }
+        if (obj.getIt() != 42) return "arrow should capture enclosing this"
+    },
+
+    test_arrow_captures_this_nested: function() {
+        var obj = {
+            value: 99,
+            getIt: function() {
+                var outer = () => {
+                    var inner = () => this.value
+                    return inner()
+                }
+                return outer()
+            }
+        }
+        if (obj.getIt() != 99) return "nested arrows should capture enclosing this"
+    },
+
+    test_arrow_this_not_rebound_by_method_call: function() {
+        var obj = {
+            value: 10,
+            getIt: function() {
+                var arrow = () => this.value
+                return arrow()
+            }
+        }
+        var other = { value: 20, stolen: obj.getIt }
+        if (other.stolen() != 20) return "setup failed"
+        if (obj.getIt() != 10) return "arrow this should come from enclosing method"
+    },
+
+    test_arrow_this_with_regular_function_this: function() {
+        var obj = {
+            value: 7,
+            getIt: function() {
+                var arrow = () => this.value
+                var regular = function() { return this }
+                if (regular() != null) return "regular fn direct call should have null this"
+                return arrow()
+            }
+        }
+        if (obj.getIt() != 7) return "arrow should capture this while regular fn does not"
+    },
+
 }