Track minimum language version for various language features (#57670)

Author: rbuckton

src/compiler/checker.ts

@@ -144,6 +144,9 @@ export const inverseJsxOptionMap = new Map(mapIterator(jsxOptionMap.entries(), (
 //       order in the generated program (see `getDefaultLibPriority` in program.ts). This
 //       order also affects overload resolution when a type declared in one lib is
 //       augmented in another lib.
+// NOTE: We must reevaluate the target for upcoming features when each successive TC39 edition is ratified in
+//       June of each year. This includes changes to `LanguageFeatureMinimumTarget`, `ScriptTarget`,
+//       transformers/esnext.ts, commandLineParser.ts, and the contents of each lib/esnext.*.d.ts file.
 const libEntries: [string, string][] = [
     // JavaScript only
     ["es5", "lib.es5.d.ts"],

src/compiler/commandLineParser.ts

@@ -71,6 +71,10 @@ const enum UsingKind {
 
 /** @internal */
 export function transformESNext(context: TransformationContext): (x: SourceFile | Bundle) => SourceFile | Bundle {
+    // NOTE: We must reevaluate the target for upcoming features when each successive TC39 edition is ratified in
+    //       June of each year. This includes changes to `LanguageFeatureMinimumTarget`, `ScriptTarget`,
+    //       transformers/esnext.ts, commandLineParser.ts, and the contents of each lib/esnext.*.d.ts file.
+
     const {
         factory,
         getEmitHelperFactory: emitHelpers,

src/compiler/transformers/esnext.ts

@@ -7277,6 +7277,9 @@ export const enum ScriptKind {
     Deferred = 7,
 }
 
+// NOTE: We must reevaluate the target for upcoming features when each successive TC39 edition is ratified in
+//       June of each year. This includes changes to `LanguageFeatureMinimumTarget`, `ScriptTarget`,
+//       transformers/esnext.ts, commandLineParser.ts, and the contents of each lib/esnext.*.d.ts file.
 export const enum ScriptTarget {
     /** @deprecated */
     ES3 = 0,
@@ -8035,6 +8038,65 @@ export type UniqueNameHandler = (baseName: string, checkFn?: (name: string) => b
 
 export type EmitHelperUniqueNameCallback = (name: string) => string;
 
+/**
+ * Indicates the minimum `ScriptTarget` (inclusive) after which a specific language feature is no longer transpiled.
+ *
+ * @internal
+ */
+export const enum LanguageFeatureMinimumTarget {
+    // ES2015 Features
+    Classes = ScriptTarget.ES2015,
+    ForOf = ScriptTarget.ES2015,
+    Generators = ScriptTarget.ES2015,
+    Iteration = ScriptTarget.ES2015,
+    SpreadElements = ScriptTarget.ES2015,
+    RestElements = ScriptTarget.ES2015,
+    TaggedTemplates = ScriptTarget.ES2015,
+    DestructuringAssignment = ScriptTarget.ES2015,
+    BindingPatterns = ScriptTarget.ES2015,
+    ArrowFunctions = ScriptTarget.ES2015,
+    BlockScopedVariables = ScriptTarget.ES2015,
+    ObjectAssign = ScriptTarget.ES2015,
+
+    // ES2016 Features
+    Exponentiation = ScriptTarget.ES2016, // `x ** y`
+
+    // ES2017 Features
+    AsyncFunctions = ScriptTarget.ES2017, // `async function f() {}`
+
+    // ES2018 Features
+    ForAwaitOf = ScriptTarget.ES2018, // `for await (const x of y)`
+    AsyncGenerators = ScriptTarget.ES2018, // `async function * f() { }`
+    AsyncIteration = ScriptTarget.ES2018, // `Symbol.asyncIterator`
+    ObjectSpreadRest = ScriptTarget.ES2018, // `{ ...obj }`
+
+    // ES2019 Features
+    BindinglessCatch = ScriptTarget.ES2019, // `try { } catch { }`
+
+    // ES2020 Features
+    BigInt = ScriptTarget.ES2020, // `0n`
+    NullishCoalesce = ScriptTarget.ES2020, // `a ?? b`
+    OptionalChaining = ScriptTarget.ES2020, // `a?.b`
+
+    // ES2021 Features
+    LogicalAssignment = ScriptTarget.ES2021, // `a ||= b`, `a &&= b`, `a ??= b`
+
+    // ES2022 Features
+    TopLevelAwait = ScriptTarget.ES2022,
+    ClassFields = ScriptTarget.ES2022,
+    PrivateNamesAndClassStaticBlocks = ScriptTarget.ES2022, // `class C { static {} #x = y, #m() {} }`, `#x in y`
+
+    // ES2023 Features
+    ShebangComments = ScriptTarget.ESNext,
+
+    // Upcoming Features
+    // NOTE: We must reevaluate the target for upcoming features when each successive TC39 edition is ratified in
+    //       June of each year. This includes changes to `LanguageFeatureMinimumTarget`, `ScriptTarget`,
+    //       transformers/esnext.ts, commandLineParser.ts, and the contents of each lib/esnext.*.d.ts file.
+    UsingAndAwaitUsing = ScriptTarget.ESNext, // `using x = y`, `await using x = y`
+    ClassAndClassElementDecorators = ScriptTarget.ESNext, // `@dec class C {}`, `class C { @dec m() {} }`
+}
+
 // dprint-ignore
 /**
  * Used by the checker, this enum keeps track of external emit helpers that should be type

src/compiler/types.ts

@@ -8,7 +8,19 @@ async function f() {
 }
 
 //// [awaitUsingDeclarationsWithImportHelpers.js]
+import { __addDisposableResource, __disposeResources } from "tslib";
 async function f() {
-    await using a = null;
+    const env_1 = { stack: [], error: void 0, hasError: false };
+    try {
+        const a = __addDisposableResource(env_1, null, true);
+    }
+    catch (e_1) {
+        env_1.error = e_1;
+        env_1.hasError = true;
+    }
+    finally {
+        const result_1 = __disposeResources(env_1);
+        if (result_1)
+            await result_1;
+    }
 }
-export {};

tests/baselines/reference/awaitUsingDeclarationsWithImportHelpers.js

@@ -8,7 +8,17 @@ export {};
 }
 
 //// [usingDeclarationsWithImportHelpers.js]
+import { __addDisposableResource, __disposeResources } from "tslib";
 {
-    using a = null;
+    const env_1 = { stack: [], error: void 0, hasError: false };
+    try {
+        const a = __addDisposableResource(env_1, null, false);
+    }
+    catch (e_1) {
+        env_1.error = e_1;
+        env_1.hasError = true;
+    }
+    finally {
+        __disposeResources(env_1);
+    }
 }
-export {};

tests/baselines/reference/usingDeclarationsWithImportHelpers.js

@@ -1,4 +1,4 @@
-// @target: esnext
+// @target: es2022
 // @module: esnext
 // @lib: esnext
 // @importHelpers: true

tests/cases/conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarationsWithImportHelpers.ts

@@ -1,4 +1,4 @@
-// @target: esnext
+// @target: es2022
 // @module: esnext
 // @lib: esnext
 // @importHelpers: true