feat(ivy): introduce typecheck package and a type constructor generator (angular#26203)

This commit introduces //packages/compiler-cli/src/ngtsc/typecheck as a
container for template type-checking code, and implements an initial API:
type constructor generation.

Type constructors are static methods on component/directive types with
no runtime implementation. The methods are used during compilation to
enable inference of a component or directive's generic type parameters
from the types of expressions bound to any of their @inputs. A type
constructor looks like:

class Directive<T> {
  someInput: T;
  static ngTypeCtor<T>(init: Partial<Pick<Directive<T>, 'someInput'>>): Directive<T>;
}

It can be used to infer a type for T based on the input:

const _dir = Directive.ngTypeCtor({someInput: 'string'}); // Directive<T>

PR Close angular#26203

Author: alxhub

packages/compiler-cli/src/ngtsc/typecheck/BUILD.bazel

@@ -0,0 +1,15 @@
+package(default_visibility = ["//visibility:public"])
+
+load("//tools:defaults.bzl", "ts_library")
+
+ts_library(
+    name = "typecheck",
+    srcs = glob(["**/*.ts"]),
+    module_name = "@angular/compiler-cli/src/ngtsc/typecheck",
+    deps = [
+        "//packages:types",
+        "//packages/compiler",
+        "//packages/compiler-cli/src/ngtsc/metadata",
+        "//packages/compiler-cli/src/ngtsc/util",
+    ],
+)

packages/compiler-cli/src/ngtsc/typecheck/src/api.ts

@@ -0,0 +1,27 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/**
+ * Metadata to generate a type constructor for a particular directive.
+*/
+export interface TypeCtorMetadata {
+  /**
+   * The name of the requested type constructor function.
+   */
+  fnName: string;
+
+  /**
+   * Whether to generate a body for the function or not.
+   */
+  body: boolean;
+
+  /**
+   * Input, output, and query field names in the type which should be included as constructor input.
+   */
+  fields: {inputs: string[]; outputs: string[]; queries: string[];};
+}

packages/compiler-cli/src/ngtsc/typecheck/src/type_constructor.ts

@@ -0,0 +1,109 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import * as ts from 'typescript';
+
+import {TypeCtorMetadata} from './api';
+
+/**
+ * Generate a type constructor for the given class and metadata.
+ *
+ * A type constructor is a specially shaped TypeScript static method, intended to be placed within
+ * a directive class itself, that permits type inference of any generic type parameters of the class
+ * from the types of expressions bound to inputs or outputs, and the types of elements that match
+ * queries performed by the directive. It also catches any errors in the types of these expressions.
+ * This method is never called at runtime, but is used in type-check blocks to construct directive
+ * types.
+ *
+ * A type constructor for NgFor looks like:
+ *
+ * static ngTypeCtor<T>(init: Partial<Pick<NgForOf<T>, 'ngForOf'|'ngForTrackBy'|'ngForTemplate'>>):
+ *   NgForOf<T>;
+ *
+ * A typical usage would be:
+ *
+ * NgForOf.ngTypeCtor(init: {ngForOf: ['foo', 'bar']}); // Infers a type of NgForOf<string>.
+ *
+ * @param node the `ts.ClassDeclaration` for which a type constructor will be generated.
+ * @param meta additional metadata required to generate the type constructor.
+ * @returns a `ts.MethodDeclaration` for the type constructor.
+ */
+export function generateTypeCtor(
+    node: ts.ClassDeclaration, meta: TypeCtorMetadata): ts.MethodDeclaration {
+  // Build rawType, a `ts.TypeNode` of the class with its generic parameters passed through from
+  // the definition without any type bounds. For example, if the class is
+  // `FooDirective<T extends Bar>`, its rawType would be `FooDirective<T>`.
+  const rawTypeArgs = node.typeParameters !== undefined ?
+      node.typeParameters.map(param => ts.createTypeReferenceNode(param.name, undefined)) :
+      undefined;
+  const rawType: ts.TypeNode = ts.createTypeReferenceNode(node.name !, rawTypeArgs);
+
+  // initType is the type of 'init', the single argument to the type constructor method.
+  // If the Directive has any inputs, outputs, or queries, its initType will be:
+  //
+  // Partial<Pick<rawType, 'inputField'|'outputField'|'queryField'>>
+  //
+  // Pick here is used to select only those fields from which the generic type parameters of the
+  // directive will be inferred. Partial is used because inputs are optional, so there may not be
+  // bindings for each field.
+  //
+  // In the special case there are no inputs/outputs/etc, initType is set to {}.
+  let initType: ts.TypeNode;
+
+  const keys: string[] = [
+    ...meta.fields.inputs,
+    ...meta.fields.outputs,
+    ...meta.fields.queries,
+  ];
+  if (keys.length === 0) {
+    // Special case - no inputs, outputs, or other fields which could influence the result type.
+    initType = ts.createTypeLiteralNode([]);
+  } else {
+    // Construct a union of all the field names.
+    const keyTypeUnion = ts.createUnionTypeNode(
+        keys.map(key => ts.createLiteralTypeNode(ts.createStringLiteral(key))));
+
+    // Construct the Pick<rawType, keyTypeUnion>.
+    const pickType = ts.createTypeReferenceNode('Pick', [rawType, keyTypeUnion]);
+
+    // Construct the Partial<pickType>.
+    initType = ts.createTypeReferenceNode('Partial', [pickType]);
+  }
+
+  // If this constructor is being generated into a .ts file, then it needs a fake body. The body
+  // is set to a return of `null!`. If the type constructor is being generated into a .d.ts file,
+  // it needs no body.
+  let body: ts.Block|undefined = undefined;
+  if (meta.body) {
+    body = ts.createBlock([
+      ts.createReturn(ts.createNonNullExpression(ts.createNull())),
+    ]);
+  }
+
+  // Create the 'init' parameter itself.
+  const initParam = ts.createParameter(
+      /* decorators */ undefined,
+      /* modifiers */ undefined,
+      /* dotDotDotToken */ undefined,
+      /* name */ 'init',
+      /* questionToken */ undefined,
+      /* type */ initType,
+      /* initializer */ undefined, );
+
+  // Create the type constructor method declaration.
+  return ts.createMethod(
+      /* decorators */ undefined,
+      /* modifiers */[ts.createModifier(ts.SyntaxKind.StaticKeyword)],
+      /* asteriskToken */ undefined,
+      /* name */ meta.fnName,
+      /* questionToken */ undefined,
+      /* typeParameters */ node.typeParameters,
+      /* parameters */[initParam],
+      /* type */ rawType,
+      /* body */ body, );
+}