Somewhat improve conditional type alias (#15811)

Co-authored-by: fisker Cheung <lionkay@gmail.com>

changelog_unreleased/typescript/15811.md

@@ -0,0 +1,24 @@
+#### Improve conditional type alias layout (#15811 by @seiyab)
+
+<!-- prettier-ignore -->
+```ts
+// Input
+type FallbackFlags<F extends Flags | undefined> =
+  Equals<NonNullableFlag<F>["flags"], {}> extends true
+    ? Dict<any>
+    : NonNullableFlag<F>["flags"];
+
+// Prettier stable
+type FallbackFlags<F extends Flags | undefined> = Equals<
+  NonNullableFlag<F>["flags"],
+  {}
+> extends true
+  ? Dict<any>
+  : NonNullableFlag<F>["flags"];
+
+// Prettier main
+type FallbackFlags<F extends Flags | undefined> =
+  Equals<NonNullableFlag<F>["flags"], {}> extends true
+    ? Dict<any>
+    : NonNullableFlag<F>["flags"];
+```

src/language-js/print/assignment.js

@@ -25,6 +25,10 @@ import {
 import { shouldInlineLogicalExpression } from "./binaryish.js";
 import { printCallExpression } from "./call-expression.js";
 
+/**
+ * @typedef {import("../../common/ast-path.js").default} AstPath
+ */
+
 function printAssignment(
   path,
   options,
@@ -147,7 +151,6 @@ function chooseLayout(path, options, print, leftDoc, rightPropertyName) {
 
   if (
     isComplexDestructuring(node) ||
-    isComplexTypeAliasParams(node) ||
     hasComplexTypeAnnotation(node) ||
     (isArrowFunctionVariableDeclarator(node) && canBreakLeftDoc)
   ) {
@@ -166,6 +169,10 @@ function chooseLayout(path, options, print, leftDoc, rightPropertyName) {
     return "break-after-operator";
   }
 
+  if (isComplexTypeAliasParams(node)) {
+    return "break-lhs";
+  }
+
   if (
     !canBreakLeftDoc &&
     (hasShortKey ||
@@ -194,7 +201,10 @@ function shouldBreakAfterOperator(path, options, print, hasShortKey) {
       return true;
     case "TSConditionalType":
     case "ConditionalTypeAnnotation":
-      if (!options.experimentalTernaries) {
+      if (
+        !options.experimentalTernaries &&
+        !shouldBreakBeforeConditionalType(rightNode)
+      ) {
         break;
       }
       return true;
@@ -435,6 +445,22 @@ function getTypeArgumentsFromCallExpression(node) {
   return (node.typeParameters ?? node.typeArguments)?.params;
 }
 
+function shouldBreakBeforeConditionalType(node) {
+  function isGeneric(subNode) {
+    switch (subNode.type) {
+      case "FunctionTypeAnnotation":
+      case "GenericTypeAnnotation":
+      case "TSFunctionType":
+      case "TSTypeReference":
+        return Boolean(subNode.typeParameters);
+      default:
+        return false;
+    }
+  }
+
+  return isGeneric(node.checkType) || isGeneric(node.extendsType);
+}
+
 export {
   isArrowFunctionVariableDeclarator,
   printAssignment,

tests/format/flow/type-alias/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,89 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`conditional.js [babel-flow] format 1`] = `
+"Unexpected token (2:43)
+  1 | type FallbackFlags<F: Flags | void> =
+> 2 |   Equals<NonNullableFlag<F>["flags"], {}> extends true
+    |                                           ^
+  3 |     ? Dict<any>
+  4 |     : NonNullableFlag<F>["flags"];
+  5 |
+Cause: Unexpected token (2:42)"
+`;
+
+exports[`conditional.js format 1`] = `
+====================================options=====================================
+parsers: ["flow"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type FallbackFlags<F: Flags | void> =
+  Equals<NonNullableFlag<F>["flags"], {}> extends true
+    ? Dict<any>
+    : NonNullableFlag<F>["flags"];
+
+    export type UnPromise<Type: Promise<mixed>> =
+    Type extends Promise<infer Generic>
+      ? Generic
+      : empty;
+
+export type Equals<X, Y> =
+  (<T>() => T extends X ? 1 : 2) extends
+  (<T>() => T extends Y ? 1 : 2)
+    ? true
+    : false;
+
+export type _Repeat<A: any, N: number, L: List = []> =
+  __Repeat<N, A, L> extends infer X
+  ? Cast<X, List>
+  : empty
+
+export type Repeat<A: any, N: number, L: List = []> =
+  N extends mixed
+  ? L extends mixed
+    ? _Repeat<A, N, L>
+    : empty
+  : empty
+
+export type Intersect<U1: any, U2: any> =
+  U1 extends mixed
+  ? U2 extends mixed
+    ? {1: U1, 0: empty}[Equals<U1, U2>]
+    : empty
+  : empty
+
+=====================================output=====================================
+type FallbackFlags<F: Flags | void> =
+  Equals<NonNullableFlag<F>["flags"], {}> extends true
+    ? Dict<any>
+    : NonNullableFlag<F>["flags"];
+
+export type UnPromise<Type: Promise<mixed>> =
+  Type extends Promise<infer Generic> ? Generic : empty;
+
+export type Equals<X, Y> =
+  (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y ? 1 : 2
+    ? true
+    : false;
+
+export type _Repeat<A: any, N: number, L: List = []> =
+  __Repeat<N, A, L> extends infer X ? Cast<X, List> : empty;
+
+export type Repeat<A: any, N: number, L: List = []> = N extends mixed
+  ? L extends mixed
+    ? _Repeat<A, N, L>
+    : empty
+  : empty;
+
+export type Intersect<U1: any, U2: any> = U1 extends mixed
+  ? U2 extends mixed
+    ? { 1: U1, 0: empty }[Equals<U1, U2>]
+    : empty
+  : empty;
+
+================================================================================
+`;
+
 exports[`issue-100857.js format 1`] = `
 ====================================options=====================================
 parsers: ["flow"]

tests/format/flow/type-alias/conditional.js

@@ -0,0 +1,34 @@
+type FallbackFlags<F: Flags | void> =
+  Equals<NonNullableFlag<F>["flags"], {}> extends true
+    ? Dict<any>
+    : NonNullableFlag<F>["flags"];
+
+    export type UnPromise<Type: Promise<mixed>> =
+    Type extends Promise<infer Generic>
+      ? Generic
+      : empty;
+
+export type Equals<X, Y> =
+  (<T>() => T extends X ? 1 : 2) extends
+  (<T>() => T extends Y ? 1 : 2)
+    ? true
+    : false;
+
+export type _Repeat<A: any, N: number, L: List = []> =
+  __Repeat<N, A, L> extends infer X
+  ? Cast<X, List>
+  : empty
+
+export type Repeat<A: any, N: number, L: List = []> =
+  N extends mixed
+  ? L extends mixed
+    ? _Repeat<A, N, L>
+    : empty
+  : empty
+
+export type Intersect<U1: any, U2: any> =
+  U1 extends mixed
+  ? U2 extends mixed
+    ? {1: U1, 0: empty}[Equals<U1, U2>]
+    : empty
+  : empty

tests/format/flow/type-alias/jsfmt.spec.js

@@ -1 +1,5 @@
-run_spec(import.meta, ["flow"]);
+run_spec(import.meta, ["flow"], {
+  errors: {
+    "babel-flow": ["conditional.js"],
+  },
+});

tests/format/typescript/type-alias/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,78 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`conditional.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type FallbackFlags<F extends Flags | undefined> =
+  Equals<NonNullableFlag<F>["flags"], {}>    extends   true
+    ? Dict<any>
+    : NonNullableFlag<F>["flags"];
+
+export type UnPromise<Type extends Promise<unknown>> =
+  Type extends Promise<infer Generic>
+    ? Generic
+    : never;
+
+export type Equals<X, Y> =
+  (<T>() => T extends X ? 1 : 2) extends
+  (<T>() => T extends Y ? 1 : 2)
+    ? true
+    : false;
+
+export type _Repeat<A extends any, N extends number, L extends List = []> =
+  __Repeat<N, A, L> extends infer X
+  ? Cast<X, List>
+  : never
+
+export type Repeat<A extends any, N extends number, L extends List = []> =
+  N extends unknown
+  ? L extends unknown
+    ? _Repeat<A, N, L>
+    : never
+  : never
+
+export type Intersect<U1 extends any, U2 extends any> =
+  U1 extends unknown
+  ? U2 extends unknown
+    ? {1: U1, 0: never}[Equals<U1, U2>]
+    : never
+  : never
+
+=====================================output=====================================
+type FallbackFlags<F extends Flags | undefined> =
+  Equals<NonNullableFlag<F>["flags"], {}> extends true
+    ? Dict<any>
+    : NonNullableFlag<F>["flags"];
+
+export type UnPromise<Type extends Promise<unknown>> =
+  Type extends Promise<infer Generic> ? Generic : never;
+
+export type Equals<X, Y> =
+  (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y ? 1 : 2
+    ? true
+    : false;
+
+export type _Repeat<A extends any, N extends number, L extends List = []> =
+  __Repeat<N, A, L> extends infer X ? Cast<X, List> : never;
+
+export type Repeat<
+  A extends any,
+  N extends number,
+  L extends List = [],
+> = N extends unknown ? (L extends unknown ? _Repeat<A, N, L> : never) : never;
+
+export type Intersect<U1 extends any, U2 extends any> = U1 extends unknown
+  ? U2 extends unknown
+    ? { 1: U1; 0: never }[Equals<U1, U2>]
+    : never
+  : never;
+
+================================================================================
+`;
+
 exports[`issue-9874.ts format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]

tests/format/typescript/type-alias/conditional.ts

@@ -0,0 +1,34 @@
+type FallbackFlags<F extends Flags | undefined> =
+  Equals<NonNullableFlag<F>["flags"], {}>    extends   true
+    ? Dict<any>
+    : NonNullableFlag<F>["flags"];
+
+export type UnPromise<Type extends Promise<unknown>> =
+  Type extends Promise<infer Generic>
+    ? Generic
+    : never;
+
+export type Equals<X, Y> =
+  (<T>() => T extends X ? 1 : 2) extends
+  (<T>() => T extends Y ? 1 : 2)
+    ? true
+    : false;
+
+export type _Repeat<A extends any, N extends number, L extends List = []> =
+  __Repeat<N, A, L> extends infer X
+  ? Cast<X, List>
+  : never
+
+export type Repeat<A extends any, N extends number, L extends List = []> =
+  N extends unknown
+  ? L extends unknown
+    ? _Repeat<A, N, L>
+    : never
+  : never
+
+export type Intersect<U1 extends any, U2 extends any> =
+  U1 extends unknown
+  ? U2 extends unknown
+    ? {1: U1, 0: never}[Equals<U1, U2>]
+    : never
+  : never