Fix sending `this` value to function environments (#526)

.editorConfig

@@ -3,3 +3,9 @@ root = true
 [{Makefile,**.mk}]
 # Use tabs for indentation (Makefiles require tabs)
 indent_style = tab
+
+[*]
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true

.vscode/tasks.json

@@ -7,14 +7,20 @@
       "type": "process",
       "label": "Cargo Run",
       "command": "cargo",
-      "args": ["run", "--bin", "boa", "./tests/js/test.js"],
-      "problemMatcher": ["$rustc"],
+      "args": [
+        "run",
+        "--bin",
+        "boa",
+        "./tests/js/test.js"
+      ],
       "group": {
         "kind": "build",
         "isDefault": true
       },
       "options": {
-        "env": { "RUST_BACKTRACE": "full" }
+        "env": {
+          "RUST_BACKTRACE": "full"
+        }
       },
       "presentation": {
         "clear": true
@@ -24,14 +30,17 @@
       "type": "process",
       "label": "Cargo Run (Profiler)",
       "command": "cargo",
-      "args": ["run", "--features", "Boa/profiler", "../tests/js/test.js"],
-      "problemMatcher": ["$rustc"],
-      "group": {
-        "kind": "build",
-        "isDefault": true
-      },
+      "args": [
+        "run",
+        "--features",
+        "Boa/profiler",
+        "../tests/js/test.js"
+      ],
+      "group": "build",
       "options": {
-        "env": { "RUST_BACKTRACE": "full" },
+        "env": {
+          "RUST_BACKTRACE": "full"
+        },
         "cwd": "${workspaceFolder}/boa_cli"
       },
       "presentation": {
@@ -42,8 +51,12 @@
       "type": "process",
       "label": "Get Tokens",
       "command": "cargo",
-      "args": ["run", "--", "-t=Debug", "./tests/js/test.js"],
-      "problemMatcher": ["$rustc"],
+      "args": [
+        "run",
+        "--",
+        "-t=Debug",
+        "./tests/js/test.js"
+      ],
       "group": "build",
       "presentation": {
         "clear": true
@@ -53,19 +66,24 @@
       "type": "process",
       "label": "Get AST",
       "command": "cargo",
-      "args": ["run", "--", "-a=Debug", "./tests/js/test.js"],
-      "problemMatcher": ["$rustc"],
+      "args": [
+        "run",
+        "--",
+        "-a=Debug",
+        "./tests/js/test.js"
+      ],
       "group": "build",
       "presentation": {
         "clear": true
-      }
+      },
     },
     {
       "type": "process",
       "label": "Cargo Test",
       "command": "cargo",
-      "args": ["test"],
-      "problemMatcher": ["$rustc"],
+      "args": [
+        "test"
+      ],
       "group": {
         "kind": "test",
         "isDefault": true
@@ -78,8 +96,10 @@
       "type": "process",
       "label": "Cargo Test Build",
       "command": "cargo",
-      "args": ["test", "--no-run"],
-      "problemMatcher": ["$rustc"],
+      "args": [
+        "test",
+        "--no-run"
+      ],
       "group": "build"
     }
   ]

boa/src/builtins/function/mod.rs

@@ -191,9 +191,18 @@ impl Function {
                     // <https://tc39.es/ecma262/#sec-prepareforordinarycall>
                     let local_env = new_function_environment(
                         function,
-                        None,
+                        if let ThisMode::Lexical = self.this_mode {
+                            None
+                        } else {
+                            Some(this.clone())
+                        },
                         self.environment.as_ref().cloned(),
-                        BindingStatus::Uninitialized,
+                        // Arrow functions do not have a this binding https://tc39.es/ecma262/#sec-function-environment-records
+                        if let ThisMode::Lexical = self.this_mode {
+                            BindingStatus::Lexical
+                        } else {
+                            BindingStatus::Uninitialized
+                        },
                     );
 
                     // Add argument bindings to the function environment
@@ -253,7 +262,12 @@ impl Function {
                         function,
                         Some(this.clone()),
                         self.environment.as_ref().cloned(),
-                        BindingStatus::Initialized,
+                        // Arrow functions do not have a this binding https://tc39.es/ecma262/#sec-function-environment-records
+                        if let ThisMode::Lexical = self.this_mode {
+                            BindingStatus::Lexical
+                        } else {
+                            BindingStatus::Uninitialized
+                        },
                     );
 
                     // Add argument bindings to the function environment

boa/src/environment/function_environment_record.rs

@@ -112,7 +112,7 @@ impl EnvironmentRecordTrait for FunctionEnvironmentRecord {
             }
             BindingStatus::Uninitialized => {
                 // TODO: change this when error handling comes into play
-                panic!("Reference Error: Unitialised binding for this function");
+                panic!("Reference Error: Uninitialised binding for this function");
             }
 
             BindingStatus::Initialized => self.this_value.clone(),

boa/src/environment/lexical_environment.rs

@@ -235,15 +235,20 @@ pub fn new_function_environment(
     outer: Option<Environment>,
     binding_status: BindingStatus,
 ) -> Environment {
-    Gc::new(GcCell::new(Box::new(FunctionEnvironmentRecord {
+    let mut func_env = FunctionEnvironmentRecord {
         env_rec: FxHashMap::default(),
         function: f,
         this_binding_status: binding_status,
         home_object: Value::undefined(),
         new_target: Value::undefined(),
         outer_env: outer, // this will come from Environment set as a private property of F - https://tc39.es/ecma262/#sec-ecmascript-function-objects
-        this_value: this.unwrap_or_else(Value::undefined),
-    })))
+        this_value: Value::undefined(),
+    };
+    // If a `this` value has been passed, bind it to the environment
+    if let Some(v) = this {
+        func_env.bind_this_value(v);
+    }
+    Gc::new(GcCell::new(Box::new(func_env)))
 }
 
 pub fn new_object_environment(object: Value, environment: Option<Environment>) -> Environment {

boa/src/exec/tests.rs

@@ -939,3 +939,19 @@ fn to_object() {
         .is_object());
     assert!(engine.to_object(&Value::null()).unwrap_err().is_object());
 }
+
+#[test]
+fn check_this_binding_in_object_literal() {
+    let realm = Realm::create();
+    let mut engine = Interpreter::new(realm);
+    let init = r#"
+        var foo = {
+            a: 3,
+            bar: function () { return this.a + 5 }
+        };
+    
+        foo.bar()
+        "#;
+
+    assert_eq!(forward(&mut engine, init), "8");
+}