Proposal: Logical Assignment Operators (#7385)

* Proposal: Logical Assignment Operators

https://github.com/jridgewell/proposal-logical-assignment

I'm bringing it [back](https://github.com/babel/babel/pull/516). 😉

* Use expectPlugin

* Add to stage 0 preset

* Add logicalAssignment missing plugin log stuff

packages/babel-core/src/transformation/util/missing-plugin-helper.js

@@ -113,6 +113,16 @@ const pluginNameMap = {
       url: "https://git.io/vb4yd",
     },
   },
+  logicalAssignment: {
+    syntax: {
+      name: "@babel/plugin-syntax-logical-assignment-operators",
+      url: "https://git.io/vAlBp",
+    },
+    transform: {
+      name: "@babel/plugin-proposal-logical-assignment-operators",
+      url: "https://git.io/vAlRe",
+    },
+  },
   nullishCoalescingOperator: {
     syntax: {
       name: "@babel/plugin-syntax-nullish-coalescing-operator",

packages/babel-plugin-proposal-logical-assignment-operators/.npmignore

@@ -0,0 +1,3 @@
+src
+test
+*.log

packages/babel-plugin-proposal-logical-assignment-operators/README.md

@@ -0,0 +1,63 @@
+# @babel/plugin-proposal-logical-assignment-operator
+
+> Transforms logical assignment operators into short-circuited assignments
+
+## Example
+
+**In**
+
+```javascript
+a ||= b;
+obj.a.b ||= c;
+
+a &&= b;
+obj.a.b &&= c;
+```
+
+**Out**
+
+```javascript
+var _obj$a, _obj$a2;
+
+a || (a = b);
+(_obj$a = obj.a).b || (_obj$a.b = c);
+
+a && (a = b);
+(_obj$a2 = obj.a).b && (_obj$a2.b = c);
+```
+
+## Installation
+
+```sh
+npm install --save-dev @babel/plugin-proposal-logical-assignment-operators
+```
+
+## Usage
+
+### Via `.babelrc` (Recommended)
+
+**.babelrc**
+
+```json
+{
+  "plugins": ["@babel/plugin-proposal-logical-assignment-operators"]
+}
+```
+
+### Via CLI
+
+```sh
+babel --plugins @babel/plugin-proposal-logical-assignment-operators script.js
+```
+
+### Via Node API
+
+```javascript
+require("@babel/core").transform("code", {
+  plugins: ["@babel/plugin-proposal-logical-assignment-operators"]
+});
+```
+
+## References
+
+* [Proposal: Logical Assignment Operators](https://github.com/jridgewell/proposal-logical-assignment-operators)

packages/babel-plugin-proposal-logical-assignment-operators/package.json

@@ -0,0 +1,21 @@
+{
+  "name": "@babel/plugin-proposal-logical-assignment-operators",
+  "version": "7.0.0-beta.40",
+  "description": "Transforms logical assignment operators into short-circuited assignments",
+  "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-proposal-logical-assignment-operators",
+  "license": "MIT",
+  "main": "lib",
+  "keywords": [
+    "babel-plugin"
+  ],
+  "dependencies": {
+    "@babel/plugin-syntax-logical-assignment-operators": "7.0.0-beta.40"
+  },
+  "peerDependencies": {
+    "@babel/core": "7.0.0-beta.40"
+  },
+  "devDependencies": {
+    "@babel/core": "7.0.0-beta.40",
+    "@babel/helper-plugin-test-runner": "7.0.0-beta.40"
+  }
+}

packages/babel-plugin-proposal-logical-assignment-operators/src/index.js

@@ -0,0 +1,42 @@
+import syntaxLogicalAssignmentOperators from "@babel/plugin-syntax-logical-assignment-operators";
+import { types as t } from "@babel/core";
+
+export default function() {
+  return {
+    inherits: syntaxLogicalAssignmentOperators,
+
+    visitor: {
+      AssignmentExpression(path) {
+        const { node, scope } = path;
+        const { operator, left, right } = node;
+        if (operator !== "||=" && operator !== "&&=") {
+          return;
+        }
+
+        let ref;
+        if (t.isMemberExpression(left)) {
+          const { object } = left;
+          const memo = scope.maybeGenerateMemoised(object);
+          if (memo) {
+            path
+              .get("left.object")
+              .replaceWith(
+                t.assignmentExpression("=", t.cloneNode(memo), object),
+              );
+
+            ref = t.cloneNode(left);
+            ref.object = t.cloneNode(memo);
+          }
+        }
+
+        path.replaceWith(
+          t.logicalExpression(
+            operator.slice(0, -1),
+            left,
+            t.assignmentExpression("=", ref || t.cloneNode(left), right),
+          ),
+        );
+      },
+    },
+  };
+}

packages/babel-plugin-proposal-logical-assignment-operators/test/fixtures/logical-assignment/general-semantics/exec.js

@@ -0,0 +1,40 @@
+var x = 0;
+var sets = 0;
+var obj = {
+  get x() {
+    return x;
+  },
+
+  set x(value) {
+    sets++;
+    x = value;
+  },
+};
+
+assert.equal(obj.x ||= 1, 1);
+assert.equal(sets, 1);
+assert.equal(obj.x ||= 2, 1);
+assert.equal(sets, 1);
+
+assert.equal(obj.x &&= 0, 0);
+assert.equal(sets, 2);
+assert.equal(obj.x &&= 3, 0);
+assert.equal(sets, 2);
+
+var gets = 0;
+var deep = {
+  get obj() {
+    gets++;
+    return obj;
+  },
+};
+
+assert.equal(deep.obj.x ||= 1, 1);
+assert.equal(gets, 1);
+assert.equal(deep.obj.x ||= 2, 1);
+assert.equal(gets, 2);
+
+assert.equal(deep.obj.x &&= 0, 0);
+assert.equal(gets, 3);
+assert.equal(deep.obj.x &&= 3, 0);
+assert.equal(gets, 4);

packages/babel-plugin-proposal-logical-assignment-operators/test/fixtures/logical-assignment/general-semantics/input.js

@@ -0,0 +1,40 @@
+var x = 0;
+var sets = 0;
+var obj = {
+  get x() {
+    return x;
+  },
+
+  set x(value) {
+    sets++;
+    x = value;
+  },
+};
+
+assert.equal(obj.x ||= 1, 1);
+assert.equal(sets, 1);
+assert.equal(obj.x ||= 2, 1);
+assert.equal(sets, 1);
+
+assert.equal(obj.x &&= 0, 0);
+assert.equal(sets, 2);
+assert.equal(obj.x &&= 3, 0);
+assert.equal(sets, 2);
+
+var gets = 0;
+var deep = {
+  get obj() {
+    gets++;
+    return obj;
+  },
+};
+
+assert.equal(deep.obj.x ||= 1, 1);
+assert.equal(gets, 1);
+assert.equal(deep.obj.x ||= 2, 1);
+assert.equal(gets, 2);
+
+assert.equal(deep.obj.x &&= 0, 0);
+assert.equal(gets, 3);
+assert.equal(deep.obj.x &&= 3, 0);
+assert.equal(gets, 4);

packages/babel-plugin-proposal-logical-assignment-operators/test/fixtures/logical-assignment/general-semantics/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["proposal-logical-assignment-operators"]
+}

packages/babel-plugin-proposal-logical-assignment-operators/test/fixtures/logical-assignment/general-semantics/output.js

@@ -0,0 +1,39 @@
+var _deep$obj, _deep$obj2, _deep$obj3, _deep$obj4;
+
+var x = 0;
+var sets = 0;
+var obj = {
+  get x() {
+    return x;
+  },
+
+  set x(value) {
+    sets++;
+    x = value;
+  }
+
+};
+assert.equal(obj.x || (obj.x = 1), 1);
+assert.equal(sets, 1);
+assert.equal(obj.x || (obj.x = 2), 1);
+assert.equal(sets, 1);
+assert.equal(obj.x && (obj.x = 0), 0);
+assert.equal(sets, 2);
+assert.equal(obj.x && (obj.x = 3), 0);
+assert.equal(sets, 2);
+var gets = 0;
+var deep = {
+  get obj() {
+    gets++;
+    return obj;
+  }
+
+};
+assert.equal((_deep$obj = deep.obj).x || (_deep$obj.x = 1), 1);
+assert.equal(gets, 1);
+assert.equal((_deep$obj2 = deep.obj).x || (_deep$obj2.x = 2), 1);
+assert.equal(gets, 2);
+assert.equal((_deep$obj3 = deep.obj).x && (_deep$obj3.x = 0), 0);
+assert.equal(gets, 3);
+assert.equal((_deep$obj4 = deep.obj).x && (_deep$obj4.x = 3), 0);
+assert.equal(gets, 4);

packages/babel-plugin-proposal-logical-assignment-operators/test/index.js

@@ -0,0 +1,3 @@
+import runner from "@babel/helper-plugin-test-runner";
+
+runner(__dirname);

packages/babel-plugin-syntax-logical-assignment-operators/.npmignore

@@ -0,0 +1,3 @@
+src
+test
+*.log

packages/babel-plugin-syntax-logical-assignment-operators/README.md

@@ -0,0 +1,35 @@
+# @babel/plugin-syntax-logical-assignment-operators
+
+> Allow parsing of the logical assignment operators.
+
+## Installation
+
+```sh
+npm install --save-dev @babel/plugin-syntax-logical-assignment-operators
+```
+
+## Usage
+
+### Via `.babelrc` (Recommended)
+
+**.babelrc**
+
+```json
+{
+  "plugins": ["@babel/plugin-syntax-logical-assignment-operators"]
+}
+```
+
+### Via CLI
+
+```sh
+babel --plugins @babel/plugin-syntax-logical-assignment-operators script.js
+```
+
+### Via Node API
+
+```javascript
+require("@babel/core").transform("code", {
+  plugins: ["@babel/plugin-syntax-logical-assignment-operators"]
+});
+```

packages/babel-plugin-syntax-logical-assignment-operators/package.json

@@ -0,0 +1,17 @@
+{
+  "name": "@babel/plugin-syntax-logical-assignment-operators",
+  "version": "7.0.0-beta.40",
+  "description": "Allow parsing of the logical assignment operators",
+  "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-syntax-logical-assignment-operators",
+  "license": "MIT",
+  "main": "lib",
+  "keywords": [
+    "babel-plugin"
+  ],
+  "peerDependencies": {
+    "@babel/core": "7.0.0-beta.40"
+  },
+  "devDependencies": {
+    "@babel/core": "7.0.0-beta.40"
+  }
+}

packages/babel-plugin-syntax-logical-assignment-operators/src/index.js

@@ -0,0 +1,7 @@
+export default function() {
+  return {
+    manipulateOptions(opts, parserOpts) {
+      parserOpts.plugins.push("logicalAssignment");
+    },
+  };
+}

packages/babel-preset-stage-0/package.json

@@ -9,6 +9,7 @@
   "main": "lib/index.js",
   "dependencies": {
     "@babel/plugin-proposal-function-bind": "7.0.0-beta.40",
+    "@babel/plugin-proposal-logical-assignment-operators": "7.0.0-beta.40",
     "@babel/preset-stage-1": "7.0.0-beta.40"
   },
   "peerDependencies": {

packages/babel-preset-stage-0/src/index.js

@@ -1,6 +1,7 @@
 import presetStage1 from "@babel/preset-stage-1";
 
 import transformFunctionBind from "@babel/plugin-proposal-function-bind";
+import transformLogicalAssignmentOperators from "@babel/plugin-proposal-logical-assignment-operators";
 
 export default function(context, opts = {}) {
   let loose = false;
@@ -22,6 +23,6 @@ export default function(context, opts = {}) {
 
   return {
     presets: [[presetStage1, { loose, useBuiltIns }]],
-    plugins: [transformFunctionBind],
+    plugins: [transformFunctionBind, transformLogicalAssignmentOperators],
   };
 }

packages/babylon/src/tokenizer/index.js

@@ -464,9 +464,16 @@ export default class Tokenizer extends LocationParser {
     const next = this.input.charCodeAt(this.state.pos + 1);
 
     if (next === code) {
+      const assign =
+        this.input.charCodeAt(this.state.pos + 2) === charCodes.equalsTo;
+      if (assign) {
+        this.expectPlugin("logicalAssignment");
+      }
       this.finishOp(
-        code === charCodes.verticalBar ? tt.logicalOR : tt.logicalAND,
-        2,
+        assign
+          ? tt.assign
+          : code === charCodes.verticalBar ? tt.logicalOR : tt.logicalAND,
+        assign ? 3 : 2,
       );
       return;
     }

packages/babylon/test/fixtures/experimental/logical-assignment-operator/and-and-equals-no-plugin/input.js

@@ -0,0 +1,2 @@
+a &&= b;
+obj.a &&= b;

packages/babylon/test/fixtures/experimental/logical-assignment-operator/and-and-equals-no-plugin/options.json

@@ -0,0 +1,4 @@
+{
+  "plugins": [],
+  "throws": "This experimental syntax requires enabling the parser plugin: 'logicalAssignment' (1:2)"
+}

packages/babylon/test/fixtures/experimental/logical-assignment-operator/and-and-equals/input.js

@@ -0,0 +1,2 @@
+a &&= b;
+obj.a &&= b;

packages/babylon/test/fixtures/experimental/logical-assignment-operator/and-and-equals/options.json

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

packages/babylon/test/fixtures/experimental/logical-assignment-operator/and-and-equals/output.json

@@ -0,0 +1,197 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 21,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 2,
+      "column": 12
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 21,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 2,
+        "column": 12
+      }
+    },
+    "sourceType": "script",
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 8,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 8
+          }
+        },
+        "expression": {
+          "type": "AssignmentExpression",
+          "start": 0,
+          "end": 7,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 7
+            }
+          },
+          "operator": "&&=",
+          "left": {
+            "type": "Identifier",
+            "start": 0,
+            "end": 1,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 0
+              },
+              "end": {
+                "line": 1,
+                "column": 1
+              },
+              "identifierName": "a"
+            },
+            "name": "a"
+          },
+          "right": {
+            "type": "Identifier",
+            "start": 6,
+            "end": 7,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 6
+              },
+              "end": {
+                "line": 1,
+                "column": 7
+              },
+              "identifierName": "b"
+            },
+            "name": "b"
+          }
+        }
+      },
+      {
+        "type": "ExpressionStatement",
+        "start": 9,
+        "end": 21,
+        "loc": {
+          "start": {
+            "line": 2,
+            "column": 0
+          },
+          "end": {
+            "line": 2,
+            "column": 12
+          }
+        },
+        "expression": {
+          "type": "AssignmentExpression",
+          "start": 9,
+          "end": 20,
+          "loc": {
+            "start": {
+              "line": 2,
+              "column": 0
+            },
+            "end": {
+              "line": 2,
+              "column": 11
+            }
+          },
+          "operator": "&&=",
+          "left": {
+            "type": "MemberExpression",
+            "start": 9,
+            "end": 14,
+            "loc": {
+              "start": {
+                "line": 2,
+                "column": 0
+              },
+              "end": {
+                "line": 2,
+                "column": 5
+              }
+            },
+            "object": {
+              "type": "Identifier",
+              "start": 9,
+              "end": 12,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 0
+                },
+                "end": {
+                  "line": 2,
+                  "column": 3
+                },
+                "identifierName": "obj"
+              },
+              "name": "obj"
+            },
+            "property": {
+              "type": "Identifier",
+              "start": 13,
+              "end": 14,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 4
+                },
+                "end": {
+                  "line": 2,
+                  "column": 5
+                },
+                "identifierName": "a"
+              },
+              "name": "a"
+            },
+            "computed": false
+          },
+          "right": {
+            "type": "Identifier",
+            "start": 19,
+            "end": 20,
+            "loc": {
+              "start": {
+                "line": 2,
+                "column": 10
+              },
+              "end": {
+                "line": 2,
+                "column": 11
+              },
+              "identifierName": "b"
+            },
+            "name": "b"
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babylon/test/fixtures/experimental/logical-assignment-operator/mallet-no-plugin/input.js

@@ -0,0 +1 @@
+a ||= b;

packages/babylon/test/fixtures/experimental/logical-assignment-operator/mallet-no-plugin/options.json

@@ -0,0 +1,4 @@
+{
+  "plugins": [],
+  "throws": "This experimental syntax requires enabling the parser plugin: 'logicalAssignment' (1:2)"
+}

packages/babylon/test/fixtures/experimental/logical-assignment-operator/mallet/input.js

@@ -0,0 +1,2 @@
+a ||= b;
+obj.a ||= b;

packages/babylon/test/fixtures/experimental/logical-assignment-operator/mallet/options.json

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

packages/babylon/test/fixtures/experimental/logical-assignment-operator/mallet/output.json

@@ -0,0 +1,197 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 21,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 2,
+      "column": 12
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 21,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 2,
+        "column": 12
+      }
+    },
+    "sourceType": "script",
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 8,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 8
+          }
+        },
+        "expression": {
+          "type": "AssignmentExpression",
+          "start": 0,
+          "end": 7,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 7
+            }
+          },
+          "operator": "||=",
+          "left": {
+            "type": "Identifier",
+            "start": 0,
+            "end": 1,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 0
+              },
+              "end": {
+                "line": 1,
+                "column": 1
+              },
+              "identifierName": "a"
+            },
+            "name": "a"
+          },
+          "right": {
+            "type": "Identifier",
+            "start": 6,
+            "end": 7,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 6
+              },
+              "end": {
+                "line": 1,
+                "column": 7
+              },
+              "identifierName": "b"
+            },
+            "name": "b"
+          }
+        }
+      },
+      {
+        "type": "ExpressionStatement",
+        "start": 9,
+        "end": 21,
+        "loc": {
+          "start": {
+            "line": 2,
+            "column": 0
+          },
+          "end": {
+            "line": 2,
+            "column": 12
+          }
+        },
+        "expression": {
+          "type": "AssignmentExpression",
+          "start": 9,
+          "end": 20,
+          "loc": {
+            "start": {
+              "line": 2,
+              "column": 0
+            },
+            "end": {
+              "line": 2,
+              "column": 11
+            }
+          },
+          "operator": "||=",
+          "left": {
+            "type": "MemberExpression",
+            "start": 9,
+            "end": 14,
+            "loc": {
+              "start": {
+                "line": 2,
+                "column": 0
+              },
+              "end": {
+                "line": 2,
+                "column": 5
+              }
+            },
+            "object": {
+              "type": "Identifier",
+              "start": 9,
+              "end": 12,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 0
+                },
+                "end": {
+                  "line": 2,
+                  "column": 3
+                },
+                "identifierName": "obj"
+              },
+              "name": "obj"
+            },
+            "property": {
+              "type": "Identifier",
+              "start": 13,
+              "end": 14,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 4
+                },
+                "end": {
+                  "line": 2,
+                  "column": 5
+                },
+                "identifierName": "a"
+              },
+              "name": "a"
+            },
+            "computed": false
+          },
+          "right": {
+            "type": "Identifier",
+            "start": 19,
+            "end": 20,
+            "loc": {
+              "start": {
+                "line": 2,
+                "column": 10
+              },
+              "end": {
+                "line": 2,
+                "column": 11
+              },
+              "identifierName": "b"
+            },
+            "name": "b"
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}