Partial application plugin

packages/babel-generator/src/generators/types.js

@@ -7,6 +7,10 @@ export function Identifier(node: Object) {
   });
 }
 
+export function ArgumentPlaceholder() {
+  this.token("?");
+}
+
 export function RestElement(node: Object) {
   this.token("...");
   this.print(node.argument, node);

packages/babel-generator/test/fixtures/types/ArgumentPlaceholder/input.js

@@ -0,0 +1,12 @@
+foo(?);
+foo(?, x);
+foo(x, ?);
+foo(?, x, ?);
+obj.foo(x, ?);
+obj.foo(?, x);
+obj.foo(?, x, ?);
+class foo {
+  constructor() {
+      baz(this, () => super.bar(?));
+  }
+}

packages/babel-generator/test/fixtures/types/ArgumentPlaceholder/options.json

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

packages/babel-generator/test/fixtures/types/ArgumentPlaceholder/output.js

@@ -0,0 +1,14 @@
+foo(?);
+foo(?, x);
+foo(x, ?);
+foo(?, x, ?);
+obj.foo(x, ?);
+obj.foo(?, x);
+obj.foo(?, x, ?);
+
+class foo {
+  constructor() {
+    baz(this, () => super.bar(?));
+  }
+
+}

packages/babel-parser/ast/spec.md

@@ -72,6 +72,7 @@ These are the core @babel/parser (babylon) AST node types.
     - [LogicalExpression](#logicalexpression)
       - [LogicalOperator](#logicaloperator)
     - [SpreadElement](#spreadelement)
+    - [ArgumentPlaceholder](#argumentplaceholder)
     - [MemberExpression](#memberexpression)
     - [BindExpression](#bindexpression)
   - [ConditionalExpression](#conditionalexpression)
@@ -862,6 +863,14 @@ interface SpreadElement <: Node {
 }
 ```
 
+### ArgumentPlaceholder
+
+```js
+interface ArgumentPlaceholder <: Node {
+    type: "ArgumentPlaceholder";
+}
+```
+
 ### MemberExpression
 
 ```js

packages/babel-parser/src/parser/expression.js

@@ -305,7 +305,6 @@ export default class ExpressionParser extends LValParser {
         const operator = this.state.value;
         node.left = left;
         node.operator = operator;
-
         if (
           operator === "**" &&
           left.type === "UnaryExpression" &&
@@ -616,6 +615,7 @@ export default class ExpressionParser extends LValParser {
         tt.parenR,
         possibleAsync,
         base.type === "Import",
+        base.type !== "Super",
       );
       if (!state.optionalChainMember) {
         this.finishCallExpression(node);
@@ -726,6 +726,7 @@ export default class ExpressionParser extends LValParser {
     close: TokenType,
     possibleAsyncArrow: boolean,
     dynamicImport?: boolean,
+    allowPlaceholder?: boolean,
   ): $ReadOnlyArray<?N.Expression> {
     const elts = [];
     let innerParenStart;
@@ -758,6 +759,7 @@ export default class ExpressionParser extends LValParser {
           false,
           possibleAsyncArrow ? { start: 0 } : undefined,
           possibleAsyncArrow ? { start: 0 } : undefined,
+          allowPlaceholder,
         ),
       );
     }
@@ -1901,6 +1903,7 @@ export default class ExpressionParser extends LValParser {
     allowEmpty: ?boolean,
     refShorthandDefaultPos: ?Pos,
     refNeedsArrowPos: ?Pos,
+    allowPlaceholder: ?boolean,
   ): ?N.Expression {
     let elt;
     if (allowEmpty && this.match(tt.comma)) {
@@ -1913,6 +1916,14 @@ export default class ExpressionParser extends LValParser {
         spreadNodeStartPos,
         spreadNodeStartLoc,
       );
+    } else if (this.match(tt.question)) {
+      this.expectPlugin("partialApplication");
+      if (!allowPlaceholder) {
+        this.raise(this.state.start, "Unexpected argument placeholder");
+      }
+      const node = this.startNode();
+      this.next();
+      elt = this.finishNode(node, "ArgumentPlaceholder");
     } else {
       elt = this.parseMaybeAssign(
         false,

packages/babel-parser/src/types.js

@@ -340,6 +340,8 @@ export type VariableDeclarator = NodeBase & {
 
 // Misc
 
+export type ArgumentPlaceholder = NodeBase & { type: "ArgumentPlaceholder" };
+
 export type Decorator = NodeBase & {
   type: "Decorator",
   expression: Expression,

packages/babel-parser/test/fixtures/experimental/partial-application/call-expr/input.js

@@ -0,0 +1 @@
+foo(?)

packages/babel-parser/test/fixtures/experimental/partial-application/call-expr/options.json

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

packages/babel-parser/test/fixtures/experimental/partial-application/call-expr/output.json

@@ -0,0 +1,99 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 6,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 6
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 6,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 6
+      }
+    },
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 6,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 6
+          }
+        },
+        "expression": {
+          "type": "CallExpression",
+          "start": 0,
+          "end": 6,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 6
+            }
+          },
+          "callee": {
+            "type": "Identifier",
+            "start": 0,
+            "end": 3,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 0
+              },
+              "end": {
+                "line": 1,
+                "column": 3
+              },
+              "identifierName": "foo"
+            },
+            "name": "foo"
+          },
+          "arguments": [
+            {
+              "type": "ArgumentPlaceholder",
+              "start": 4,
+              "end": 5,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 4
+                },
+                "end": {
+                  "line": 1,
+                  "column": 5
+                }
+              }
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/partial-application/call-on-SuperProperty/input.js

@@ -0,0 +1,5 @@
+class foo {
+    constructor() {
+        baz(this, () => super.bar(?));
+    }
+}

packages/babel-parser/test/fixtures/experimental/partial-application/call-on-SuperProperty/options.json

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