Monomorphize generic overload calls and call generic methods through Pick views (#1511)

packages/compiler/src/frontend/lowering/generic-functions.ts

@@ -268,10 +268,13 @@ export function genericCallInstance(
   {
     const rdecl = rsig ? rsig.declaration : undefined;
     if (
+      rsig &&
       rdecl &&
       (ts.isFunctionDeclaration(rdecl) || ts.isMethodDeclaration(rdecl)) &&
       !rdecl.body
     ) {
+      const overload = overloadCallInstance(lowerer, expr, info, rsig, rdecl);
+      if (overload) return overload;
       lowerer.unsupported(
         "SC1090",
         expr,
@@ -317,23 +320,11 @@ export function genericCallInstance(
   // different fields). Non-literal bindings (a key union, plain string)
   // share one runtime-keyed instance per IR signature, exactly the
   // widened discipline.
-  const keyofTps = keyofConstrainedTypeParams(info);
-  if (keyofTps.size > 0) {
+  if (keyofConstrainedTypeParams(info).size > 0) {
     const tsBindings = new Map<ts.Symbol, ts.Type>();
     const bindings = lowerer.inferTypeParamBindings(expr, info, rsig, tsBindings);
-    const litKey = info.typeParams
-      .filter((tp) => keyofTps.has(tp))
-      .map((tp) => {
-        const bound = tsBindings.get(tp);
-        return bound?.isStringLiteralType()
-          ? JSON.stringify(bound.value)
-          : bound?.isNumberLiteralType()
-            ? String(bound.value)
-            : "*";
-      })
-      .join(",");
     return internGenericInstance(lowerer, expr, info, params, returnType, () => bindings, {
-      extraKey: `@${litKey}`,
+      extraKey: keyofLiteralKey(info, tsBindings),
       tsBindings,
     });
   }
@@ -342,6 +333,98 @@ export function genericCallInstance(
   );
 }
 
+/** A call that resolved to an OVERLOAD signature of a generic function
+ * or method with an implementation (`request<T>(p: WithHandler<T>):
+ * Promise<T>; request(p: Plain): Promise<Res>; request<T>(p: Params<T>)
+ * {...}`): the implementation monomorphizes under the bindings the
+ * overload's resolved signature proves for its type parameters (the
+ * structural unification every generic call uses, run against the
+ * overload; unbound parameters take their declared defaults). The
+ * instance's parameters and result are the IMPLEMENTATION's under those
+ * bindings — the body was checked against them — and the call's
+ * arguments and result coerce across, exactly as a non-generic overload
+ * call reconciles with its implementation (parameters the overload omits
+ * must be optional in the implementation). Null when the overload does
+ * not belong to this implementation or the arities do not line up. */
+function overloadCallInstance(
+  lowerer: Lowerer,
+  expr: ts.CallExpression,
+  info: GenericFnInfo,
+  rsig: ts.Signature,
+  rdecl: ts.FunctionDeclaration | ts.MethodDeclaration,
+): GenericInstance | null {
+  const impl = info.decl;
+  if (
+    rdecl.parent !== impl.parent ||
+    rdecl.name === undefined ||
+    impl.name === undefined ||
+    rdecl.name.getText() !== impl.name.getText() ||
+    rdecl.parameters.nodes.length > impl.parameters.nodes.length ||
+    impl.parameters.nodes
+      .slice(rdecl.parameters.nodes.length)
+      .some((p) => p.questionToken === undefined && p.initializer === undefined) ||
+    rdecl.parameters.nodes.some((p) => p.dotDotDotToken !== undefined)
+  )
+    return null;
+  const declSig = lowerer.checker.getSignatureFromDeclaration(impl);
+  if (!declSig) return null;
+  const tsBindings = new Map<ts.Symbol, ts.Type>();
+  const bindings = new Map<ts.Symbol, IrType>();
+  unifySignatureBindings(lowerer, info, rsig, bindings, tsBindings);
+  // Explicit type arguments name the OVERLOAD's type parameters, which
+  // need not match the implementation's in order: the resolved overload
+  // already carries them, so unification binds first, and an explicit
+  // argument binds only a still-unbound implementation parameter of the
+  // same name.
+  const overloadTps = rdecl.typeParameters?.nodes ?? [];
+  expr.typeArguments?.nodes.forEach((ta, i) => {
+    const name = overloadTps[i]?.name.text;
+    const tp = info.typeParams.find((p) => p.name === name);
+    if (!tp || bindings.has(tp)) return;
+    const taT = lowerer.checker.getTypeFromTypeNode(ta);
+    const mapped = lowerer.mapTypeOf(taT);
+    if (mapped) {
+      bindings.set(tp, mapped);
+      tsBindings.set(tp, taT);
+    }
+  });
+  bindDefaultTypeParams(lowerer, info.typeParams, impl.typeParameters?.nodes, bindings, tsBindings);
+  // A type parameter the overload never mentions (a handler the overload
+  // omits) is `unknown`, the checker's own answer for an uninferred one.
+  for (const tp of info.typeParams) {
+    if (bindings.has(tp)) continue;
+    bindings.set(tp, DYN);
+    tsBindings.set(tp, lowerer.checker.getUnknownType());
+  }
+  const previous = lowerer.typeParamBindings;
+  const previousTs = lowerer.typeParamTsBindings;
+  lowerer.typeParamBindings = bindings;
+  lowerer.typeParamTsBindings = tsBindings;
+  let params: ParamShape[];
+  let returnType: IrType | null;
+  try {
+    params = paramShapes(
+      lowerer,
+      impl.parameters.nodes,
+      declSig,
+      (_param, i) => expr.arguments.nodes[i] ?? expr,
+    );
+    returnType = lowerer.mapTypeOf(lowerer.checker.getReturnTypeOfSignature(declSig));
+  } finally {
+    lowerer.typeParamBindings = previous;
+    lowerer.typeParamTsBindings = previousTs;
+  }
+  if (!returnType) return null;
+  // keyof-constrained parameters key their instance on the bound literal,
+  // as on the implementation-signature path.
+  return internGenericInstance(lowerer, expr, info, params, returnType, () => bindings, {
+    ...(keyofConstrainedTypeParams(info).size > 0
+      ? { extraKey: keyofLiteralKey(info, tsBindings) }
+      : {}),
+    tsBindings,
+  });
+}
+
 /** A generic factory whose result is one of its own local classes
  * (`function base<T>(v: T) { return class { value: T = v }; }`). Each
  * instance has its own class, so the instance is keyed on its bindings and
@@ -570,6 +653,25 @@ function keyofConstrainedTypeParams(info: GenericFnInfo): Set<ts.Symbol> {
   return out;
 }
 
+/** The instance-key suffix of the literals bound to `info`'s
+ * keyof-constrained type parameters (`@"a"`; `*` for a non-literal
+ * binding): two literals can map to one IR signature while their bodies
+ * read different fields. */
+function keyofLiteralKey(info: GenericFnInfo, tsBindings: Map<ts.Symbol, ts.Type>): string {
+  const keyofTps = keyofConstrainedTypeParams(info);
+  const literals = info.typeParams
+    .filter((tp) => keyofTps.has(tp))
+    .map((tp) => {
+      const bound = tsBindings.get(tp);
+      return bound?.isStringLiteralType()
+        ? JSON.stringify(bound.value)
+        : bound?.isNumberLiteralType()
+          ? String(bound.value)
+          : "*";
+    });
+  return `@${literals.join(",")}`;
+}
+
 /** Type-parameter symbol → concrete IR type for one instantiation.
  * Explicit type arguments bind directly; the rest come from structurally
  * matching each DECLARED param/return type (which mentions the type
@@ -705,6 +807,27 @@ function unifySignatureBindings(
         // so match it against the whole remaining union. Removing null
         // too is safe only when no undeclared null arm remains.
         unify(dParts[0]!, lowerer.checker.getNonNullableType(inst), depth + 1);
+      } else if (dParts.length > 1 && iParts.length === dParts.length) {
+        // `T | Promise<T>` against `Res | Promise<Res>`: each declared
+        // part that names a generic target (Promise, an interface, an
+        // alias) pairs with the one instantiated part of the same target;
+        // a single remaining bare type parameter takes the single
+        // remaining instantiated part.
+        const remaining = [...iParts];
+        const bare: ts.Type[] = [];
+        for (const d of dParts) {
+          if (d.flags & ts.TypeFlags.TypeParameter) {
+            bare.push(d);
+            continue;
+          }
+          const target = d.getSymbol() ?? d.getAliasSymbol();
+          if (target === undefined) return;
+          const matches = remaining.filter((i) => (i.getSymbol() ?? i.getAliasSymbol()) === target);
+          if (matches.length !== 1) return;
+          remaining.splice(remaining.indexOf(matches[0]!), 1);
+          unify(d, matches[0]!, depth + 1);
+        }
+        if (bare.length === 1 && remaining.length === 1) unify(bare[0]!, remaining[0]!, depth + 1);
       }
       return;
     }

packages/compiler/src/frontend/lowering/lower-calls.ts

@@ -3309,6 +3309,8 @@ function lowerDynReceiverMethodCall(
   // any-elemented array). Typed receivers keep their own lowerings.
   const recvTs = lowerer.typeOf(access.expression);
   if (lowerer.classImplementedProtocol(recvTs)) {
+    const viewed = pickViewGenericMethodCall(lowerer, call, access, recvTs);
+    if (viewed) return viewed;
     const property = lowerer.checker.getPropertyOfType(recvTs, access.name.text);
     if (
       property &&
@@ -10092,3 +10094,49 @@ function maybePromiseHandlerResult(
   }
   return stmt;
 }
+
+/** `view.m(args)` where `view` is a `Pick<C, K>` / `Omit<C, K>` view of a
+ * program class C and `m` is one of C's GENERIC methods (its overloads
+ * included): generic methods have no dispatchable method value, so the
+ * view's live receiver is extracted as the C instance it holds (a checked
+ * extraction — a value of another class throws Node-style TypeError
+ * text naming C) and the call monomorphizes statically against C, the
+ * same lowering a C-typed receiver gets. Null for other receivers. */
+function pickViewGenericMethodCall(
+  lowerer: Lowerer,
+  call: ts.CallExpression,
+  access: ts.PropertyAccessExpression,
+  recvTs: ts.Type,
+): IrExpr | null {
+  const alias = recvTs.getAliasSymbol();
+  if (alias === undefined || (alias.name !== "Pick" && alias.name !== "Omit")) return null;
+  if (!alias.declarations.every((d) => d.getSourceFile().isDeclarationFile)) return null;
+  const source = recvTs.getAliasTypeArguments()[0];
+  const symbol = source?.getSymbol();
+  const info = symbol ? lowerer.classBySymbol.get(symbol) : undefined;
+  if (!info || call.questionDotToken || access.questionDotToken) return null;
+  const found = findGenericMethodOn(lowerer, info, access.name.text);
+  if (!found) return null;
+  const loc = locOf(access.expression);
+  const lowered = lowerer.lowerExpr(access.expression);
+  const instance: IrType = { kind: "object", className: info.def.name };
+  // A view that statically holds an instance of another class (a
+  // structurally compatible one) calls that class's method in Node, not
+  // C's: the call is refused rather than extracted as a C instance.
+  if (
+    lowered.type.kind === "object" &&
+    lowered.type.className !== info.def.name &&
+    !lowerer.isSubclassOf(lowered.type.className, info.def.name)
+  ) {
+    lowerer.unsupported(
+      "SC1090",
+      access,
+      `calling the generic method '${access.name.text}' through a '${alias.name}' view of '${info.def.name}' that holds a '${lowerer.fmt(lowered.type)}'`,
+    );
+  }
+  const receiver: IrExpr =
+    lowered.type.kind === "object"
+      ? lowered
+      : { kind: "dynCheck", value: lowerer.coerceToExpected(lowered, DYN), type: instance, loc };
+  return lowerClassGenericMethodCall(lowerer, call, access, info, found, receiver);
+}

packages/compiler/src/frontend/type-mapper.ts

@@ -6340,6 +6340,10 @@ function dynSubsumableUnionArm(arm: IrType, ctx: TypeMapperCtx): boolean {
       return true;
     case "record":
     case "array":
+    // `T | Promise<T>` with T bound to `unknown`: the checked-dynamic value
+    // holds a promise by reference, so `unknown` absorbs the promise arm
+    // exactly as the checker's own union reduction does.
+    case "promise":
       return canConvertToDyn(
         arm,
         (id) => ctx.shapes.get(id),

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6495-generic-method-overloads.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6495-generic-method-overloads.ts"
+ ],
+ "diags": []
+}

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6496-overload-signatures.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6496-overload-signatures.ts"
+ ],
+ "diags": []
+}

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6497-generic-overload-bindings.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6497-generic-overload-bindings.ts"
+ ],
+ "diags": []
+}

packages/compiler/test/ts7/baselines/order-parity/tests/diagnostics/overload-fences.ts.json

@@ -1,6 +0,0 @@
-{
- "order": [
-  "<repo>/tests/diagnostics/overload-fences.ts"
- ],
- "diags": []
-}

packages/compiler/test/ts7/baselines/order-parity/tests/diagnostics/pick-view-generic-methods.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/diagnostics/pick-view-generic-methods.ts"
+ ],
+ "diags": []
+}

tests/corpus/6495-generic-method-overloads.ts

@@ -0,0 +1,54 @@
+// Calls that resolve to OVERLOAD signatures of a generic method or
+// function: the implementation monomorphizes under what the overload
+// proves for its type parameters (a parameter the overload never mentions
+// is unknown), directly and through a `Pick` view of the class, whose
+// live receiver keeps the instance's state. `T | Promise<T>` callbacks
+// bind T from either arm.
+interface Reply {
+  code: number;
+  text: string;
+}
+type Mapper<T> = (reply: Reply) => T | Promise<T>;
+
+class Store {
+  loads = 0;
+  async load<T>(key: string, map: Mapper<T>): Promise<T>;
+  async load(key: string): Promise<Reply>;
+  async load<T>(key: string, map?: Mapper<T>): Promise<T | Reply> {
+    this.loads++;
+    const reply: Reply = { code: 200, text: key };
+    if (map === undefined) return reply;
+    return await map(reply);
+  }
+}
+
+interface Services {
+  store: Pick<Store, "load">;
+}
+
+function pick<T>(items: T[], index: number): T;
+function pick<T>(items: T[]): T;
+function pick<T>(items: T[], index = 0): T {
+  return items[index]!;
+}
+
+async function settle<T>(reply: Reply, map?: Mapper<T>): Promise<T | Reply> {
+  return map ? await map(reply) : reply;
+}
+
+async function main(): Promise<void> {
+  const store = new Store();
+  const plain = await store.load("alpha");
+  console.log(plain.code, plain.text);
+  const length = await store.load("beta", (reply) => reply.text.length);
+  console.log(length * 2);
+  const services: Services = { store };
+  const viaView = await services.store.load("gamma");
+  const upper = await services.store.load("delta", async (reply) => reply.text.toUpperCase());
+  console.log(viaView.text, upper, store.loads);
+  console.log(pick(["x", "y"]), pick([1, 2, 3], 2));
+  console.log(JSON.stringify(await settle<Reply>({ code: 1, text: "s" })));
+  console.log(await settle({ code: 2, text: "tt" }, (reply) => reply.code + reply.text.length));
+}
+
+main();

tests/corpus/6496-overload-signatures.ts

@@ -1,7 +1,7 @@
-// The overload fences that REMAIN now that overload signatures lower:
-// generic overload calls (the per-instantiation body would be typed
-// against a signature it was never checked under), and the multi-
-// signature type surfacing where a binding needs it spelled.
+// Overload signatures: a generic overload call monomorphizes the
+// implementation under the bindings the overload proves (a parameter the
+// overload omits is optional in the implementation), and an immutable
+// alias of an overloaded declaration projects onto the implementation.
 function twice<T>(x: T): T[];
 function twice<T>(x: T, n: number): T[];
 function twice<T>(x: T, n?: number): T[] {

tests/corpus/6497-generic-overload-bindings.ts

@@ -0,0 +1,34 @@
+// Bindings of generic overload calls: explicit type arguments name the
+// overload's type parameters, which can be declared in another order than
+// the implementation's, and keyof-constrained parameters bound to
+// different literals through an overload read their own fields.
+function tag<B, A>(value: A, label: B): string;
+function tag<A, B>(value: A, label?: B): string {
+  return `${typeof value}:${typeof label}:${String(value)}${String(label)}`;
+}
+console.log(tag<string, number>(5, "x"));
+console.log(tag<boolean, string>("y", true));
+
+class Labels {
+  prefix = "#";
+  render<B, A>(value: A, label: B): string;
+  render<A, B>(value: A, label?: B): string {
+    return `${this.prefix}${typeof value}/${typeof label}`;
+  }
+}
+console.log(new Labels().render<number, string>("z", 7));
+
+interface Row {
+  a: number;
+  b: number;
+  name: string;
+}
+function read<T, K extends keyof T>(row: T, key: K): T[K];
+function read<T, K extends keyof T>(row: T, key: K, fallback: T[K]): T[K];
+function read<T, K extends keyof T>(row: T, key: K, fallback?: T[K]): T[K] {
+  const value = row[key];
+  return value === undefined ? fallback! : value;
+}
+const row: Row = { a: 1, b: 2, name: "r" };
+console.log(read(row, "a"), read(row, "b"), read(row, "name"));
+console.log(read(row, "b", 0) + read(row, "a", 0));

tests/diagnostics/pick-view-generic-methods.ts

@@ -0,0 +1,16 @@
+// A generic method called through a `Pick` view of a class compiles
+// against that class. A view that holds an instance of a structurally
+// compatible, unrelated class is refused: Node calls that class's own
+// method.
+class Store {
+  load<T>(key: string, map: (text: string) => T): T {
+    return map(key);
+  }
+}
+class Mirror {
+  load<T>(key: string, map: (text: string) => T): T {
+    return map(`${key}!`);
+  }
+}
+const view: Pick<Store, "load"> = new Mirror();
+console.log(view.load("k", (text) => text.length));

tests/harness/__snapshots__/overload-fences.ts.txt

@@ -1,6 +0,0 @@
-overload-fences.ts:12:13 - error SC1090: calls selecting an overload signature of a generic function (only the implementation signature monomorphizes) is not supported yet
-
-  11 | }
-  12 | console.log(twice("q").length);
-     |             ^~~~~~~~~~
-  13 | function pick(x: "a"): string;

tests/harness/__snapshots__/pick-view-generic-methods.ts.txt

@@ -0,0 +1,6 @@
+pick-view-generic-methods.ts:16:13 - error SC1090: calling the generic method 'load' through a 'Pick' view of 'Store' that holds a 'Mirror' is not supported yet
+
+  15 | const view: Pick<Store, "load"> = new Mirror();
+  16 | console.log(view.load("k", (text) => text.length));
+     |             ^~~~~~~~~
+  17 | 

tests/harness/corpus-costs/6495-generic-method-overloads.ts.json

@@ -0,0 +1 @@
+{ "plain": 2783, "san": 2211 }

tests/harness/corpus-costs/6496-overload-signatures.ts.json

@@ -0,0 +1 @@
+{ "plain": 2032, "san": 1924 }

tests/harness/corpus-costs/6497-generic-overload-bindings.ts.json

@@ -0,0 +1 @@
+{ "plain": 2061, "san": 1900 }