Throw on attempt to delete a private field

Given that private fields can only be used within classes, any code
using them must be in a strict mode context. As private fields cannot
be deleted, throw an early SyntaxError.

src/parser/expression.js

@@ -252,8 +252,16 @@ export default class ExpressionParser extends LValParser {
 
       if (update) {
         this.checkLVal(node.argument, undefined, undefined, "prefix operation");
-      } else if (this.state.strict && node.operator === "delete" && node.argument.type === "Identifier") {
+      } else if (this.state.strict && node.operator === "delete") {
-        this.raise(node.start, "Deleting local variable in strict mode");
+        const arg = node.argument;
+
+        if (arg.type === "Identifier") {
+          this.raise(node.start, "Deleting local variable in strict mode");
+        } else if (this.hasPlugin("classPrivateProperties")) {
+          if (arg.type === "PrivateName" || (arg.type === "MemberExpression" && arg.property.type === "PrivateName")) {
+            this.raise(node.start, "Deleting a private field is not allowed");
+          }
+        }
       }
 
       return this.finishNode(node, update ? "UpdateExpression" : "UnaryExpression");

test/fixtures/experimental/class-private-properties/delete-non-private/actual.js

@@ -0,0 +1,6 @@
+class Foo {
+  #x;
+  constructor() {
+    delete #x.d;
+  }
+}

test/fixtures/experimental/class-private-properties/delete-non-private/expected.json

@@ -0,0 +1,275 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 58,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 6,
+      "column": 1
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 58,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 6,
+        "column": 1
+      }
+    },
+    "sourceType": "script",
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start": 0,
+        "end": 58,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 6,
+            "column": 1
+          }
+        },
+        "id": {
+          "type": "Identifier",
+          "start": 6,
+          "end": 9,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 6
+            },
+            "end": {
+              "line": 1,
+              "column": 9
+            },
+            "identifierName": "Foo"
+          },
+          "name": "Foo"
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start": 10,
+          "end": 58,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 10
+            },
+            "end": {
+              "line": 6,
+              "column": 1
+            }
+          },
+          "body": [
+            {
+              "type": "ClassPrivateProperty",
+              "start": 14,
+              "end": 17,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 2
+                },
+                "end": {
+                  "line": 2,
+                  "column": 5
+                }
+              },
+              "key": {
+                "type": "Identifier",
+                "start": 15,
+                "end": 16,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 3
+                  },
+                  "end": {
+                    "line": 2,
+                    "column": 4
+                  },
+                  "identifierName": "x"
+                },
+                "name": "x"
+              },
+              "value": null
+            },
+            {
+              "type": "ClassMethod",
+              "start": 20,
+              "end": 56,
+              "loc": {
+                "start": {
+                  "line": 3,
+                  "column": 2
+                },
+                "end": {
+                  "line": 5,
+                  "column": 3
+                }
+              },
+              "static": false,
+              "computed": false,
+              "key": {
+                "type": "Identifier",
+                "start": 20,
+                "end": 31,
+                "loc": {
+                  "start": {
+                    "line": 3,
+                    "column": 2
+                  },
+                  "end": {
+                    "line": 3,
+                    "column": 13
+                  },
+                  "identifierName": "constructor"
+                },
+                "name": "constructor"
+              },
+              "kind": "constructor",
+              "id": null,
+              "generator": false,
+              "expression": false,
+              "async": false,
+              "params": [],
+              "body": {
+                "type": "BlockStatement",
+                "start": 34,
+                "end": 56,
+                "loc": {
+                  "start": {
+                    "line": 3,
+                    "column": 16
+                  },
+                  "end": {
+                    "line": 5,
+                    "column": 3
+                  }
+                },
+                "body": [
+                  {
+                    "type": "ExpressionStatement",
+                    "start": 40,
+                    "end": 52,
+                    "loc": {
+                      "start": {
+                        "line": 4,
+                        "column": 4
+                      },
+                      "end": {
+                        "line": 4,
+                        "column": 16
+                      }
+                    },
+                    "expression": {
+                      "type": "UnaryExpression",
+                      "start": 40,
+                      "end": 51,
+                      "loc": {
+                        "start": {
+                          "line": 4,
+                          "column": 4
+                        },
+                        "end": {
+                          "line": 4,
+                          "column": 15
+                        }
+                      },
+                      "operator": "delete",
+                      "prefix": true,
+                      "argument": {
+                        "type": "MemberExpression",
+                        "start": 47,
+                        "end": 51,
+                        "loc": {
+                          "start": {
+                            "line": 4,
+                            "column": 11
+                          },
+                          "end": {
+                            "line": 4,
+                            "column": 15
+                          }
+                        },
+                        "object": {
+                          "type": "PrivateName",
+                          "start": 48,
+                          "end": 49,
+                          "loc": {
+                            "start": {
+                              "line": 4,
+                              "column": 12
+                            },
+                            "end": {
+                              "line": 4,
+                              "column": 13
+                            }
+                          },
+                          "name": {
+                            "type": "Identifier",
+                            "start": 48,
+                            "end": 49,
+                            "loc": {
+                              "start": {
+                                "line": 4,
+                                "column": 12
+                              },
+                              "end": {
+                                "line": 4,
+                                "column": 13
+                              },
+                              "identifierName": "x"
+                            },
+                            "name": "x"
+                          }
+                        },
+                        "property": {
+                          "type": "Identifier",
+                          "start": 50,
+                          "end": 51,
+                          "loc": {
+                            "start": {
+                              "line": 4,
+                              "column": 14
+                            },
+                            "end": {
+                              "line": 4,
+                              "column": 15
+                            },
+                            "identifierName": "d"
+                          },
+                          "name": "d"
+                        },
+                        "computed": false
+                      },
+                      "extra": {
+                        "parenthesizedArgument": false
+                      }
+                    }
+                  }
+                ],
+                "directives": []
+              }
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}

test/fixtures/experimental/class-private-properties/delete-non-private/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["classProperties", "classPrivateProperties"]
+}

test/fixtures/experimental/class-private-properties/failure-delete-private-property/actual.js

@@ -0,0 +1,6 @@
+class Foo {
+  #x;
+  constructor() {
+    delete this.#x;
+  }
+}

test/fixtures/experimental/class-private-properties/failure-delete-private-property/options.json

@@ -0,0 +1,7 @@
+{
+  "throws": "Deleting a private field is not allowed (4:4)",
+  "plugins": [
+    "classProperties",
+    "classPrivateProperties"
+    ]
+}

test/fixtures/experimental/class-private-properties/failure-delete-shorthand/actual.js

@@ -0,0 +1,6 @@
+class Foo {
+  #x;
+  constructor() {
+    delete #x;
+  }
+}

test/fixtures/experimental/class-private-properties/failure-delete-shorthand/options.json

@@ -0,0 +1,7 @@
+{
+  "throws": "Deleting a private field is not allowed (4:4)",
+  "plugins": [
+    "classProperties",
+    "classPrivateProperties"
+    ]
+}