Deprecate `module` syntax #62876

RyanCavanaugh · 2025-12-10T21:56:37Z

This changes the existing suggestion diagnostic to an error when you write forms like module foo or module foo.bar {

~~The ambient form declare module foo { is still ok~~ edit: no, we agreed in #62211 to also deprecate that form, as is the ambient module declaration form declare module "specifier" {

Copilot

Pull request overview

This PR deprecates the non-ambient module keyword syntax in TypeScript, changing it from a suggestion diagnostic to an error. The change enforces that developers use namespace instead of module for namespace declarations, while still allowing declare module for ambient declarations and declare module "specifier" for module augmentation.

Key changes:

Changed the diagnostic from a suggestion to an error for non-ambient module declarations
Updated the condition to exclude ambient contexts from the error
Updated all test cases to use namespace instead of module

Reviewed changes

Copilot reviewed 88 out of 88 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
`src/compiler/checker.ts`	Modified the check to emit an error instead of a suggestion diagnostic for non-ambient module declarations, and removed unused import
`tests/cases/fourslash/moduleDeclarationDeprecated_suggestion1.ts`	Removed test file that checked for suggestion diagnostics
`tests/cases/fourslash/moduleDeclarationDeprecated_suggestion2.ts`	Removed test file that checked for empty suggestion diagnostics
`tests/cases/compiler/moduleKeywordDeprecated.ts`	Added new test file to verify error behavior for non-ambient `module` declarations
`tests/cases/conformance/internalModules/DeclarationMerging/*.ts`	Updated test cases to use `namespace` instead of `module`
`tests/cases/compiler/*.ts`	Updated multiple test cases to use `namespace` instead of deprecated `module` keyword
`tests/baselines/reference/*.{types,symbols,js,errors.txt}`	Updated baseline files to reflect changes from `module` to `namespace`

Comments suppressed due to low confidence (2)

tests/cases/compiler/escapedIdentifiers.ts:1

The declare keyword was added to convert this non-ambient module declaration to an ambient one. However, this changes the semantics of the code beyond just updating the keyword. If this was previously a non-ambient module declaration, it should be changed to namespace moduleType\u0032 instead.
tests/baselines/reference/moduleKeywordDeprecated.errors.txt:1
The error diagnostic is still labeled as "suggestion" in the baseline output, but according to the PR description and the code changes, it should now be an error. The diagnostic level should be "error" instead of "suggestion".

RyanCavanaugh · 2025-12-10T22:34:53Z

@typescript-bot test top800

typescript-bot · 2025-12-10T22:34:58Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`test top800`	✅ Started	✅ Results

tests/cases/compiler/escapedIdentifiers.ts

jakebailey · 2025-12-11T00:09:53Z

tests/baselines/reference/dottedModuleName2.errors.txt

@@ -0,0 +1,58 @@
+dottedModuleName2.ts(22,8): suggestion TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.


The message in diagnosticMessage.json should be updated to "error"

typescript-bot · 2025-12-11T00:58:46Z

@RyanCavanaugh Here are the results of running the top 800 repos with tsc comparing main and refs/pull/62876/merge:

Everything looks good!

DanielRosenwasser · 2025-12-11T08:30:41Z

@typescript-bot pack this

typescript-bot · 2025-12-11T08:30:48Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`pack this`	✅ Started	✅ Results

typescript-bot · 2025-12-11T08:35:03Z

Hey @DanielRosenwasser, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/166787/artifacts?artifactName=tgz&fileId=5B5A1DC78D2CF32FC54B5EBC8ACD09579FF86E294083153584D973D89884D14D02&fileName=/typescript-6.0.0-insiders.20251211.tgz"
    }
}

and then running npm install.

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/[email protected]".;

robpalme · 2025-12-11T09:31:12Z

Thanks for the pack. A quick try out suggest that when you provoke the intended checker error, it crashes.

Error: Debug Failure. Should never get an Info diagnostic on the command line.
    at getCategoryFormat (/home/projects/stackblitz-starters-ybxu3fvk/node_modules/typescript/lib/_tsc.js:121656:20)
    at formatDiagnosticsWithColorAndContext (/home/projects/stackblitz-starters-ybxu3fvk/node_modules/typescript/lib/_tsc.js:121721:71)

RyanCavanaugh · 2025-12-11T16:52:03Z

A quick try out suggest that when you provoke the intended checker error, it crashes.

Well, that's one way to get people to change their code 🤦

RyanCavanaugh · 2025-12-11T17:03:08Z

@typescript-bot test top800
@typescript-bot pack this

typescript-bot · 2025-12-11T17:03:12Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`test top800`	✅ Started	👀 Results
`pack this`	✅ Started	✅ Results

tests/baselines/reference/escapedIdentifiers.errors.txt

typescript-bot · 2025-12-11T17:07:19Z

Hey @RyanCavanaugh, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/166789/artifacts?artifactName=tgz&fileId=F7B95EBDF36B0403901B7D4CB436D9FE693D2E5245B7A658F1362E103A40D18402&fileName=/typescript-6.0.0-insiders.20251211.tgz"
    }
}

and then running npm install.

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/[email protected]".;

robpalme · 2025-12-11T18:05:42Z

The new pack works great. No crashes!

And it correctly errors on the declare form. Thank you for that update 💙

The only issue I observe is that for all forms, the error squiggles are on the identifier, not the keyword. Which seems a bit misleading.

index.ts:3:16 - error TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.

3 declare module types {
                 ~~~~~


Found 1 error in index.ts:3

typescript-bot · 2025-12-11T19:28:05Z

@RyanCavanaugh Here are the results of running the top 800 repos with tsc comparing main and refs/pull/62876/merge:

Something interesting changed - please have a look.

Details

microsoft/vscode

11 of 63 projects failed to build with the old tsc and were ignored

src/tsconfig.tsec.json

error TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.

src/tsconfig.monaco.json

error TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.
- src/vs/editor/standalone/browser/standaloneServices.ts#L1174
- src/vs/platform/sign/browser/signService.ts#L14

jakebailey · 2025-12-11T21:19:15Z

@typescript-bot test top800

typescript-bot · 2025-12-11T21:19:20Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`test top800`	✅ Started	✅ Results

typescript-bot · 2025-12-11T23:44:46Z

@jakebailey Here are the results of running the top 800 repos with tsc comparing main and refs/pull/62876/merge:

Everything looks good!

jakebailey

So long, module

RyanCavanaugh added 3 commits December 10, 2025 13:51

Update tests and baselines

9707ef2

Ban non-ambient uses of module keyword

6f07a90

Add test

5fb6474

Copilot AI review requested due to automatic review settings December 10, 2025 21:56

github-project-automation bot added this to PR Backlog Dec 10, 2025

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github-project-automation bot moved this to Not started in PR Backlog Dec 10, 2025

typescript-bot added Author: Team For Uncommitted Bug PR for untriaged, rejected, closed or missing bug labels Dec 10, 2025

Copilot started reviewing on behalf of RyanCavanaugh December 10, 2025 21:57 View session

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knip'd

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typescript-bot added For Milestone Bug PRs that fix a bug with a specific milestone and removed For Uncommitted Bug PR for untriaged, rejected, closed or missing bug labels Dec 11, 2025

Update to also error in ambient contexts; fix more tests

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jakebailey mentioned this pull request Dec 11, 2025

Replace old-style TS modules with namespaces microsoft/vscode#282862

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github-project-automation bot moved this from Not started to Needs merge in PR Backlog Dec 12, 2025

RyanCavanaugh added this pull request to the merge queue Dec 12, 2025

Merged via the queue into microsoft:main with commit 16b933f Dec 12, 2025
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RyanCavanaugh deleted the deprecateModules branch December 12, 2025 00:30

github-project-automation bot moved this from Needs merge to Done in PR Backlog Dec 12, 2025

jakebailey pushed a commit to jakebailey/TypeScript that referenced this pull request Dec 12, 2025

Deprecate module syntax (microsoft#62876)

b6e4c25

robpalme mentioned this pull request Dec 12, 2025

[Feat] TypeScript 6.0 compatibility via [email protected] visgl/react-map-gl#2561

Open

nicolo-ribaudo mentioned this pull request Dec 12, 2025

Drop support for TS module <identifier> babel/babel#17659

Open

		@@ -0,0 +1,58 @@
		dottedModuleName2.ts(22,8): suggestion TS1540: A 'namespace' declaration should not be declared using the 'module' keyword. Please use the 'namespace' keyword instead.

Deprecate module syntax #62876

Deprecate module syntax #62876

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Deprecate `module` syntax #62876

Deprecate `module` syntax #62876

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