diff --git a/CHANGELOG.md b/CHANGELOG.md
index e881b6b4c38..72abaa86733 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,38 @@
# Changelog
+## Breaking changes
+
+* Add support for TypeScript's `preserveValueImports` setting ([#1525](https://github.com/evanw/esbuild/issues/1525))
+
+ TypeScript 4.5, which was just released, added [a new setting called `preserveValueImports`](https://devblogs.microsoft.com/typescript/announcing-typescript-4-5/#preserve-value-imports). This release of esbuild implements support for this new setting. However, this release also changes esbuild's behavior regarding the `importsNotUsedAsValues` setting, so this release is being considered a breaking change. Now esbuild's behavior should more accurately match the behavior of the TypeScript compiler. This is described in more detail below.
+
+ The difference in behavior is around unused imports. By default, unused import names are considered to be types and are completely removed if they are unused. If all import names are removed for a given import statement, then the whole import statement is removed too. The two `tsconfig.json` settings [`importsNotUsedAsValues`](https://www.typescriptlang.org/tsconfig#importsNotUsedAsValues) and [`preserveValueImports`](https://www.typescriptlang.org/tsconfig#preserveValueImports) let you customize this. Here's what the TypeScript compiler's output looks like with these different settings enabled:
+
+ ```ts
+ // Original code
+ import { unused } from "foo";
+
+ // Default output
+ /* (the import is completely removed) */
+
+ // Output with "importsNotUsedAsValues": "preserve"
+ import "foo";
+
+ // Output with "preserveValueImports": true
+ import { unused } from "foo";
+ ```
+
+ Previously, since the `preserveValueImports` setting didn't exist yet, esbuild had treated the `importsNotUsedAsValues` setting as if it were what is now the `preserveValueImports` setting instead. This was a deliberate deviation from how the TypeScript compiler behaves, but was necessary to allow esbuild to be used as a TypeScript-to-JavaScript compiler inside of certain composite languages such as Svelte and Vue. These languages append additional code after converting the TypeScript to JavaScript so unused imports may actually turn out to be used later on:
+
+ ```svelte
+
+
+ ```
+
+ Previously the implementers of these languages had to use the `importsNotUsedAsValues` setting as a hack for esbuild to preserve the import statements. With this release, esbuild now follows the behavior of the TypeScript compiler so implementers will need to use the new `preserveValueImports` setting to do this instead. This is the breaking change.
+
## 0.13.15
* Fix `super` in lowered `async` arrow functions ([#1777](https://github.com/evanw/esbuild/issues/1777))
diff --git a/internal/bundler/bundler.go b/internal/bundler/bundler.go
index 2d7456e2b01..fea150bb225 100644
--- a/internal/bundler/bundler.go
+++ b/internal/bundler/bundler.go
@@ -1114,8 +1114,8 @@ func (s *scanner) maybeParseFile(
if resolveResult.UseDefineForClassFieldsTS != config.Unspecified {
optionsClone.UseDefineForClassFields = resolveResult.UseDefineForClassFieldsTS
}
- if resolveResult.PreserveUnusedImportsTS {
- optionsClone.PreserveUnusedImportsTS = true
+ if resolveResult.UnusedImportsTS != config.UnusedImportsRemoveStmt {
+ optionsClone.UnusedImportsTS = resolveResult.UnusedImportsTS
}
optionsClone.TSTarget = resolveResult.TSTarget
diff --git a/internal/bundler/bundler_tsconfig_test.go b/internal/bundler/bundler_tsconfig_test.go
index bab62c9f216..cae6902c1b7 100644
--- a/internal/bundler/bundler_tsconfig_test.go
+++ b/internal/bundler/bundler_tsconfig_test.go
@@ -1090,11 +1090,7 @@ func TestTsconfigPreserveUnusedImports(t *testing.T) {
})
}
-// This must preserve the import clause even though all imports are not used as
-// values. THIS BEHAVIOR IS A DEVIATION FROM THE TYPESCRIPT COMPILER! It exists
-// to support the use case of compiling partial modules for compile-to-JavaScript
-// languages such as Svelte.
-func TestTsconfigPreserveUnusedImportClause(t *testing.T) {
+func TestTsconfigImportsNotUsedAsValuesPreserve(t *testing.T) {
tsconfig_suite.expectBundled(t, bundled{
files: map[string]string{
"/Users/user/project/src/entry.ts": `
@@ -1123,6 +1119,35 @@ func TestTsconfigPreserveUnusedImportClause(t *testing.T) {
})
}
+func TestTsconfigPreserveValueImports(t *testing.T) {
+ tsconfig_suite.expectBundled(t, bundled{
+ files: map[string]string{
+ "/Users/user/project/src/entry.ts": `
+ import {x, y} from "./foo"
+ import z from "./foo"
+ import * as ns from "./foo"
+ console.log(1 as x, 2 as z, 3 as ns.y)
+ `,
+ "/Users/user/project/src/tsconfig.json": `{
+ "compilerOptions": {
+ "preserveValueImports": true
+ }
+ }`,
+ },
+ entryPaths: []string{"/Users/user/project/src/entry.ts"},
+ options: config.Options{
+ Mode: config.ModeConvertFormat,
+ OutputFormat: config.FormatESModule,
+ AbsOutputFile: "/Users/user/project/out.js",
+ ExternalModules: config.ExternalModules{
+ AbsPaths: map[string]bool{
+ "/Users/user/project/src/foo": true,
+ },
+ },
+ },
+ })
+}
+
func TestTsconfigTarget(t *testing.T) {
tsconfig_suite.expectBundled(t, bundled{
files: map[string]string{
diff --git a/internal/bundler/snapshots/snapshots_tsconfig.txt b/internal/bundler/snapshots/snapshots_tsconfig.txt
index a2bae996345..bfc7ef16ae0 100644
--- a/internal/bundler/snapshots/snapshots_tsconfig.txt
+++ b/internal/bundler/snapshots/snapshots_tsconfig.txt
@@ -198,6 +198,14 @@ var test_default = 123;
// Users/user/project/src/entry.ts
console.log(test_default);
+================================================================================
+TestTsconfigImportsNotUsedAsValuesPreserve
+---------- /Users/user/project/out.js ----------
+import "./foo";
+import "./foo";
+import "./foo";
+console.log(1, 2, 3);
+
================================================================================
TestTsconfigJsonAbsoluteBaseUrl
---------- /Users/user/project/out.js ----------
@@ -319,14 +327,6 @@ var require_util = __commonJS({
var import_util = __toModule(require_util());
console.log((0, import_util.default)());
-================================================================================
-TestTsconfigPreserveUnusedImportClause
----------- /Users/user/project/out.js ----------
-import { x, y } from "./foo";
-import z from "./foo";
-import * as ns from "./foo";
-console.log(1, 2, 3);
-
================================================================================
TestTsconfigPreserveUnusedImports
---------- /Users/user/project/out.js ----------
@@ -334,6 +334,14 @@ TestTsconfigPreserveUnusedImports
import "./src/foo";
console.log(1);
+================================================================================
+TestTsconfigPreserveValueImports
+---------- /Users/user/project/out.js ----------
+import { x, y } from "./foo";
+import z from "./foo";
+import * as ns from "./foo";
+console.log(1, 2, 3);
+
================================================================================
TestTsconfigRemoveUnusedImports
---------- /Users/user/project/out.js ----------
diff --git a/internal/config/config.go b/internal/config/config.go
index d8ab71e9831..4fa90437122 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -223,7 +223,7 @@ type Options struct {
WriteToStdout bool
OmitRuntimeForTests bool
- PreserveUnusedImportsTS bool
+ UnusedImportsTS UnusedImportsTS
UseDefineForClassFields MaybeBool
ASCIIOnly bool
KeepNames bool
@@ -284,6 +284,29 @@ type Options struct {
Stdin *StdinInfo
}
+type UnusedImportsTS uint8
+
+const (
+ // "import { unused } from 'foo'" => "" (TypeScript's default behavior)
+ UnusedImportsRemoveStmt UnusedImportsTS = iota
+
+ // "import { unused } from 'foo'" => "import 'foo'" ("importsNotUsedAsValues" != "remove")
+ UnusedImportsKeepStmtRemoveValues
+
+ // "import { unused } from 'foo'" => "import { unused } from 'foo'" ("preserveValueImports" == true)
+ UnusedImportsKeepValues
+)
+
+func UnusedImportsFromTsconfigValues(preserveImportsNotUsedAsValues bool, preserveValueImports bool) UnusedImportsTS {
+ if preserveValueImports {
+ return UnusedImportsKeepValues
+ }
+ if preserveImportsNotUsedAsValues {
+ return UnusedImportsKeepStmtRemoveValues
+ }
+ return UnusedImportsRemoveStmt
+}
+
type TSTarget struct {
Source logger.Source
Range logger.Range
diff --git a/internal/js_parser/js_parser.go b/internal/js_parser/js_parser.go
index ef92d1916bd..d2dcfc816ec 100644
--- a/internal/js_parser/js_parser.go
+++ b/internal/js_parser/js_parser.go
@@ -337,7 +337,7 @@ type optionsThatSupportStructuralEquality struct {
omitRuntimeForTests bool
ignoreDCEAnnotations bool
treeShaking bool
- preserveUnusedImportsTS bool
+ unusedImportsTS config.UnusedImportsTS
useDefineForClassFields config.MaybeBool
}
@@ -363,7 +363,7 @@ func OptionsFromConfig(options *config.Options) Options {
omitRuntimeForTests: options.OmitRuntimeForTests,
ignoreDCEAnnotations: options.IgnoreDCEAnnotations,
treeShaking: options.TreeShaking,
- preserveUnusedImportsTS: options.PreserveUnusedImportsTS,
+ unusedImportsTS: options.UnusedImportsTS,
useDefineForClassFields: options.UseDefineForClassFields,
},
}
@@ -13054,19 +13054,12 @@ func (p *parser) scanForImportsAndExports(stmts []js_ast.Stmt) (result importsEx
case *js_ast.SImport:
record := &p.importRecords[s.ImportRecordIndex]
- // The official TypeScript compiler always removes unused imported
- // symbols. However, we deliberately deviate from the official
- // TypeScript compiler's behavior doing this in a specific scenario:
- // we are not bundling, symbol renaming is off, and the tsconfig.json
- // "importsNotUsedAsValues" setting is present and is not set to
- // "remove".
- //
- // This exists to support the use case of compiling partial modules for
- // compile-to-JavaScript languages such as Svelte. These languages try
- // to reference imports in ways that are impossible for esbuild to know
- // about when esbuild is only given a partial module to compile. Here
- // is an example of some Svelte code that might use esbuild to convert
- // TypeScript to JavaScript:
+ // We implement TypeScript's "preserveValueImports" tsconfig.json setting
+ // to support the use case of compiling partial modules for compile-to-
+ // JavaScript languages such as Svelte. These languages try to reference
+ // imports in ways that are impossible for TypeScript and esbuild to know
+ // about when they are only given a partial module to compile. Here is an
+ // example of some Svelte code that contains a TypeScript snippet:
//
//