feat: add support for PartialApplication

CHANGELOG.unreleased.md

@@ -44,6 +44,42 @@ const link = <a href="example.com">http://example.com</a>;
 
 -->
 
+#### JavaScript: add support for PartialApplication ([#6397] by [@JounQin])
+
+Previous versions would not be able to format this syntax, this has been fixed in this version.
+
+<!-- prettier-ignore -->
+```js
+const addOne = add(1, ?); // apply from the left
+addOne(2); // 3
+
+const addTen = add(?, 10); // apply from the right
+addTen(2); // 12
+
+// with pipeline
+let newScore = player.score
+  |> add(7, ?)
+  |> clamp(0, 100, ?); // shallow stack, the pipe to `clamp` is the same frame as the pipe to `add`.
+
+// Output (Prettier stable)
+SyntaxError: Unexpected token (1:23)
+> 1 | const addOne = add(1, ?); // apply from the left
+    |                       ^
+  2 | addOne(2); // 3
+  3 |
+  4 | const addTen = add(?, 10); // apply from the right
+
+// Output (Prettier master)
+const addOne = add(1, ?); // apply from the left
+addOne(2); // 3
+
+const addTen = add(?, 10); // apply from the right
+addTen(2); // 12
+
+// with pipeline
+let newScore = player.score |> add(7, ?) |> clamp(0, 100, ?); // shallow stack, the pipe to \`clamp\` is the same frame as the pipe to \`add\`.
+```
+
 #### JavaScript: More readable parentheses for new-call ([#6412] by [@bakkot])
 
 <!-- prettier-ignore -->
@@ -995,6 +1031,7 @@ class A {
 [#6340]: https://github.com/prettier/prettier/pull/6340
 [#6377]: https://github.com/prettier/prettier/pull/6377
 [#6381]: https://github.com/prettier/prettier/pull/6381
+[#6397]: https://github.com/prettier/prettier/pull/6397
 [#6404]: https://github.com/prettier/prettier/pull/6404
 [#6411]: https://github.com/prettier/prettier/pull/6411
 [#6412]: https://github.com/prettier/prettier/pull/6412

src/language-js/parser-babylon.js

@@ -39,7 +39,8 @@ function babelOptions(extraOptions, extraPlugins) {
         "throwExpressions",
         "logicalAssignment",
         "classPrivateMethods",
-        "v8intrinsic"
+        "v8intrinsic",
+        "partialApplication"
       ].concat(extraPlugins)
     },
     extraOptions

src/language-js/printer-estree.js

@@ -3506,6 +3506,9 @@ function printPathNoParens(path, options, print, args) {
         " as ",
         path.call(print, "alias")
       ]);
+
+    case "ArgumentPlaceholder":
+      return "?";
     default:
       /* istanbul ignore next */
       throw new Error("unknown type: " + JSON.stringify(n.type));

tests/partial_application/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,31 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`test.js 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+const addOne = add(1, ?); // apply from the left
+addOne(2); // 3
+
+const addTen = add(?, 10); // apply from the right
+addTen(2); // 12
+
+// with pipeline
+let newScore = player.score
+  |> add(7, ?)
+  |> clamp(0, 100, ?); // shallow stack, the pipe to \`clamp\` is the same frame as the pipe to \`add\`.
+
+=====================================output=====================================
+const addOne = add(1, ?); // apply from the left
+addOne(2); // 3
+
+const addTen = add(?, 10); // apply from the right
+addTen(2); // 12
+
+// with pipeline
+let newScore = player.score |> add(7, ?) |> clamp(0, 100, ?); // shallow stack, the pipe to \`clamp\` is the same frame as the pipe to \`add\`.
+
+================================================================================
+`;

tests/partial_application/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, ["babel"]);

tests/partial_application/test.js

@@ -0,0 +1,10 @@
+const addOne = add(1, ?); // apply from the left
+addOne(2); // 3
+
+const addTen = add(?, 10); // apply from the right
+addTen(2); // 12
+
+// with pipeline
+let newScore = player.score
+  |> add(7, ?)
+  |> clamp(0, 100, ?); // shallow stack, the pipe to `clamp` is the same frame as the pipe to `add`.