verbatimModuleSyntax enables isolatedModules errors, even when isolatedModules is disabled

[daniele-orlando]

🔎 Search Terms

enum, verbatimModuleSyntax, isolatedModules

🕗 Version & Regression Information

TypeScript: 5.5.3

• This changed between versions 5.4 and 5.5

⏯ Playground Link

Reproduction Project

💻 Code

See the attached project.

🙁 Actual behavior

verbatimModuleSyntax = false
isolatedModules = undefined

npx -p [email protected] tsc --showConfig -p tsconfig.verbatime-false.json | grep isolatedModules
// outputs nothing.
// CORRECT

npx -p [email protected] tsc --noEmit -p tsconfig.verbatime-false.json
// PASSES

---

verbatimModuleSyntax = true
isolatedModules = undefined

npx -p [email protected] tsc --showConfig -p tsconfig.verbatime-true.json | grep isolatedModules
// outputs "isolatedModules": true.
// WRONG

npx -p [email protected] tsc --noEmit -p tsconfig.verbatime-true.json
// FAILS
// ... has a string type, but must have syntactically recognizable string syntax when 'isolatedModules' is enabled.

---

verbatimModuleSyntax = true
isolatedModules = false

npx -p [email protected] tsc --showConfig -p tsconfig.verbatime-true,isolated-false.json | grep isolatedModules
// outputs "isolatedModules": false.
// CORRECT

// BUT
npx -p [email protected] tsc --noEmit -p tsconfig.verbatime-true,isolated-false.json
// FAILS
// ... has a string type, but must have syntactically recognizable string syntax when 'isolatedModules' is enabled.

🙂 Expected behavior

Setting verbatimModuleSyntax: true should not enable isolatedModules.
Setting verbatimModuleSyntax: true and isolatedModules: false should disable isolatedModules.

[daniele-orlando]

At the attention of: @weswigham

[RyanCavanaugh]

It's always been the intent of VMS to be a superset of IM, see #51479 (comment)

[daniele-orlando]

Thanks for the clarification.

I think it should be documented inside the doc that verbatimModuleSyntax implies isolatedModules. From what I can see, there is not mention in the Reference TSConfig Documentation.

[daniele-orlando]

How/where can I report the issue about the documentation?

[jakebailey]

If you send a PR to https://github.com/microsoft/TypeScript-Website/blob/4503af71d2c4ae95cbc4188a4ce29ca272bd9f57/packages/tsconfig-reference/scripts/tsconfigRules.ts#L201 which marks isolatedModules: trueIf("verbatimModuleSyntax"), that would update the site to show that.

[daniele-orlando]

Thank you very much @jakebailey. Following you suggestion I opened a PR for the doc website.

microsoft/TypeScript-Website#3179.

[daniele-orlando]

I close this issue as it is a documentation issue.