Partial Application Syntax: Stage 1 (#9343)

* add partial application syntax and some tests

* remove unnecessary error message and hasPartial function from parseNewArguments

* add types for PartialExpression

* Update the tests

* rename PartialExpression to Partial

* move Partial from expressions to types and rename to ArgumentPlaceholder

* add tests for ArgumentPlaceholder in babel-generator

* rename Partial to ArgumentPlaceholder

* update the tests

* remove alias from the type and undo changes in generated folder

* adds a nice error message

* better definition for the type

* auto-generated files

* update the conditional for allowPlaceholder message and tests

* update CallExpression definition to accept ArgumentPlaceholder

* change description

* clean up

* indent ArgumentPlaceholder entry and revert unwanted changes

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

@@ -323,7 +323,6 @@ export default class ExpressionParser extends LValParser {
         const operator = this.state.value;
         node.left = left;
         node.operator = operator;
-
         if (
           operator === "**" &&
           left.type === "UnaryExpression" &&
@@ -634,6 +633,7 @@ export default class ExpressionParser extends LValParser {
         tt.parenR,
         possibleAsync,
         base.type === "Import",
+        base.type !== "Super",
       );
       if (!state.optionalChainMember) {
         this.finishCallExpression(node);
@@ -744,6 +744,7 @@ export default class ExpressionParser extends LValParser {
     close: TokenType,
     possibleAsyncArrow: boolean,
     dynamicImport?: boolean,
+    allowPlaceholder?: boolean,
   ): $ReadOnlyArray<?N.Expression> {
     const elts = [];
     let innerParenStart;
@@ -776,6 +777,7 @@ export default class ExpressionParser extends LValParser {
           false,
           possibleAsyncArrow ? { start: 0 } : undefined,
           possibleAsyncArrow ? { start: 0 } : undefined,
+          allowPlaceholder,
         ),
       );
     }
@@ -1945,6 +1947,7 @@ export default class ExpressionParser extends LValParser {
     allowEmpty: ?boolean,
     refShorthandDefaultPos: ?Pos,
     refNeedsArrowPos: ?Pos,
+    allowPlaceholder: ?boolean,
   ): ?N.Expression {
     let elt;
     if (allowEmpty && this.match(tt.comma)) {
@@ -1957,6 +1960,14 @@ 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,