perf(ts): use extends constraints on infer

RebeccaStevens · Jun 15, 2022 · f053e76 · f053e76
1 parent 20241c5
commit f053e76
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Showing 4 changed files with 439 additions and 25 deletions.
diff --git a/package.json b/package.json
@@ -50,7 +50,12 @@
         "dist/node/types/legacy/v4_0.d.ts"
       ]
     },
-    ">=4.1": {
+    "<4.7": {
+      "*": [
+        "dist/node/types/legacy/v4_6.d.ts"
+      ]
+    },
+    ">=4.7": {
       "*": [
         "dist/node/types/current/index.d.ts"
       ]

diff --git a/src/types/defaults.ts b/src/types/defaults.ts
@@ -108,17 +108,18 @@ type DeepMergeRecordsDefaultHKTInternalPropValueHelper<
   K extends PropertyKey,
   M,
   Acc extends ReadonlyArray<unknown>
-> = Ts extends readonly [infer Head, ...infer Rest]
-  ? Head extends Readonly<Record<PropertyKey, unknown>>
-    ? Rest extends readonly [unknown, ...ReadonlyArray<unknown>]
-      ? DeepMergeRecordsDefaultHKTInternalPropValueHelper<
-          Rest,
-          K,
-          M,
-          [...Acc, ValueOfKey<Head, K>]
-        >
-      : [...Acc, ValueOfKey<Head, K>]
-    : never
+> = Ts extends readonly [
+  infer Head extends Readonly<Record<PropertyKey, unknown>>,
+  ...infer Rest
+]
+  ? Rest extends readonly [unknown, ...ReadonlyArray<unknown>]
+    ? DeepMergeRecordsDefaultHKTInternalPropValueHelper<
+        Rest,
+        K,
+        M,
+        [...Acc, ValueOfKey<Head, K>]
+      >
+    : [...Acc, ValueOfKey<Head, K>]
   : never;
 
 /**
@@ -138,15 +139,16 @@ type DeepMergeArraysDefaultHKTHelper<
   MF extends DeepMergeMergeFunctionsURIs,
   M,
   Acc extends ReadonlyArray<unknown>
-> = Ts extends readonly [infer Head, ...infer Rest]
-  ? Head extends ReadonlyArray<unknown>
-    ? Rest extends readonly [
-        ReadonlyArray<unknown>,
-        ...ReadonlyArray<ReadonlyArray<unknown>>
-      ]
-      ? DeepMergeArraysDefaultHKTHelper<Rest, MF, M, [...Acc, ...Head]>
-      : [...Acc, ...Head]
-    : never
+> = Ts extends readonly [
+  infer Head extends ReadonlyArray<unknown>,
+  ...infer Rest
+]
+  ? Rest extends readonly [
+      ReadonlyArray<unknown>,
+      ...ReadonlyArray<ReadonlyArray<unknown>>
+    ]
+    ? DeepMergeArraysDefaultHKTHelper<Rest, MF, M, [...Acc, ...Head]>
+    : [...Acc, ...Head]
   : never;
 
 /**

diff --git a/tests/deepmerge-custom.test.ts b/tests/deepmerge-custom.test.ts
@@ -121,10 +121,10 @@ declare module "../src/types" {
     MF extends DeepMergeMergeFunctionsURIs,
     M
   > {
-    readonly CustomArrays2: Ts extends Readonly<readonly [...infer Es]>
-      ? Es extends ReadonlyArray<unknown>
-        ? unknown[]
-        : never
+    readonly CustomArrays2: Ts extends Readonly<
+      readonly [ReadonlyArray<unknown>]
+    >
+      ? unknown[]
       : never;
     readonly CustomOthers2: string;
   }