Optimize Schema.Class decoding (#6733)

Author: gcanti

.changeset/optimize-schema-class-decoding.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Avoid validating `Schema.Class` fields twice when decoding.

packages/effect/src/Schema.ts

@@ -14145,7 +14145,14 @@ function makeClass<
 
 function getClassTransformation(self: new(...args: ReadonlyArray<any>) => any) {
   return new SchemaTransformation.Transformation<any, any, never, never>(
-    SchemaGetter.transform((input) => new self(input)),
+    SchemaGetter.transform((input) =>
+      new self(input, {
+        "~payload": {
+          token: payloadToken,
+          value: input
+        }
+      })
+    ),
     SchemaGetter.passthrough()
   )
 }

packages/effect/test/schema/Schema.test.ts

@@ -6433,6 +6433,22 @@ Expected a value between -2147483648 and 2147483647, got 9007199254740992`
       deepStrictEqual(Effect.runSync(A.makeEffect()), new A())
     })
 
+    it("decoding validates the class struct once", () => {
+      let checks = 0
+      const schema = Schema.Struct({
+        a: Schema.String
+      }).check(Schema.makeFilter(() => {
+        checks++
+        return true
+      }))
+      class A extends Schema.Class<A>("A")(schema) {}
+
+      const instance = Schema.decodeUnknownSync(A)({ a: "a" })
+
+      assertTrue(instance instanceof A)
+      strictEqual(checks, 1)
+    })
+
     it("suspend before initialization", async () => {
       const schema = Schema.suspend(() => string)
       class A extends Schema.Class<A>("A")(Schema.Struct({ a: schema })) {}
@@ -6752,6 +6768,33 @@ Expected a value between -2147483648 and 2147483647, got 9007199254740992`
         await decoding.succeed({ a: "a", b: 2 }, new B({ a: "a", b: 2 }))
       })
 
+      it("decoding validates the extended struct once", () => {
+        let baseChecks = 0
+        let extensionChecks = 0
+        class A extends Schema.Class<A>("A")(
+          Schema.Struct({
+            a: Schema.String
+          }).check(Schema.makeFilter(() => {
+            baseChecks++
+            return true
+          }))
+        ) {}
+        class B extends A.extend<B>("B")(
+          Schema.Struct({
+            b: Schema.Number
+          }).check(Schema.makeFilter(() => {
+            extensionChecks++
+            return true
+          }))
+        ) {}
+
+        const instance = Schema.decodeUnknownSync(B)({ a: "a", b: 1 })
+
+        assertTrue(instance instanceof B)
+        strictEqual(baseChecks, 1)
+        strictEqual(extensionChecks, 1)
+      })
+
       it("constructor preserves subclass fields while ignoring excess properties by default", () => {
         class A extends Schema.Class<A>("A")({
           a: Schema.String