Flow: fix function type param (#8365)

changelog_unreleased/flow/pr-8365.md

@@ -0,0 +1,19 @@
+#### Fix function type param contains nullable param ([#8365](https://github.com/prettier/prettier/pull/8365) by [@fisker](https://github.com/fisker))
+
+<!-- prettier-ignore -->
+```flow
+// Input
+let f: <A>(
+  ((?A) => B),
+) => B;
+
+// Prettier stable
+let f: <A>((?A) => B) => B;
+
+// Prettier stable (Second format)
+SyntaxError: Unexpected token (1:12)
+> 1 | let f: <A>((?A) => B) => B;
+
+// Prettier master
+let f: <A>(((?A) => B)) => B;
+```

src/language-js/needs-parens.js

@@ -456,7 +456,16 @@ function needsParens(path, options) {
         // We should check ancestor's parent to know whether the parentheses
         // are really needed, but since ??T doesn't make sense this check
         // will almost never be true.
-        ancestor.type === "NullableTypeAnnotation"
+        ancestor.type === "NullableTypeAnnotation" ||
+        // See #5283
+        (parent.type === "FunctionTypeParam" &&
+          parent.name === null &&
+          node.params &&
+          node.params.some(
+            (param) =>
+              param.typeAnnotation &&
+              param.typeAnnotation.type === "NullableTypeAnnotation"
+          ))
       );
     }
 

tests/flow/function-type-param/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,32 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`issue-5283.js format 1`] = `
+====================================options=====================================
+parsers: ["flow", "babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+
+let f: <A>((
+  (?A) => B
+)) => B;
+
+
+export const testFunctionOnOptionsAsArgument: <T1,a>(?a, ((?a) => T1)) => T1 = function _(Arg1, Arg2) { const result = TypesBS.testFunctionOnOptionsAsArgument((Arg1 == null ? undefined : Arg1), Arg2); return result };
+
+=====================================output=====================================
+let f: <A>(((?A) => B)) => B;
+
+export const testFunctionOnOptionsAsArgument: <T1, a>(
+  ?a,
+  ((?a) => T1)
+) => T1 = function _(Arg1, Arg2) {
+  const result = TypesBS.testFunctionOnOptionsAsArgument(
+    Arg1 == null ? undefined : Arg1,
+    Arg2
+  );
+  return result;
+};
+
+================================================================================
+`;

tests/flow/function-type-param/issue-5283.js

@@ -0,0 +1,7 @@
+
+let f: <A>((
+  (?A) => B
+)) => B;
+
+
+export const testFunctionOnOptionsAsArgument: <T1,a>(?a, ((?a) => T1)) => T1 = function _(Arg1, Arg2) { const result = TypesBS.testFunctionOnOptionsAsArgument((Arg1 == null ? undefined : Arg1), Arg2); return result };

tests/flow/function-type-param/jsfmt.spec.js

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