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--experimental-strip-types should elide imported types #230
Description
Node Version: v22.9.0
Command: node --experimental-strip-types example.ts
import { Http2SecureServer } from 'http2'; // causes error
//import type { Http2SecureServer } from 'http2'; // no error
console.log('done');import { Http2SecureServer } from 'http2'; // causes error
^^^^^^^^^^^^^^^^^
SyntaxError: The requested module 'http2' does not provide an export named 'Http2SecureServer'
at ModuleJob._instantiate (node:internal/modules/esm/module_job:171:21)
at async ModuleJob.run (node:internal/modules/esm/module_job:254:5)
at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:483:26)
When I import a built in type using import type ... everything seems OK. I wonder if -experimental-strip-types needs to rewrite imports in some cases?
Activity
davidfiala commentedon Oct 9, 2024
Apologies- this was in part my mistake.
Http2SecureServeris not exported bynode:http2. The user error was that the IDE and bundler let me get away with the import without using thetypekeyword.I think this does bring up an interesting question though: bundlers disregard things exported as a type and only used as a type. It's much harder for
--experimental-strip-typesto know which imports it can disregard until after it's done a full pass of the source code. And even then, I wonder if it's idempotent to skip any import that was never used as anything except a type.aduh95 commentedon Oct 9, 2024
According to the spec, importing a specific named imports should not be observable IIUC (i.e.
import {whatever} from 'specifier'andimport 'specifier'should be equivalent as long aswhateveris not used). That being said, it's probably quite tricky to reliably assess whether something is only used as a type, and would come with some speed tradeoff I assume.FWIW, there's
verbatimModuleSyntaxto avoid this trap – as well as a lint rule.davidfiala commentedon Oct 10, 2024
Thank you for the tips!
nicolo-ribaudo commentedon Oct 10, 2024
It's is impossible to determine that reliably (because the binding could be re-exported). That's why typescript introduced isolatedModules very long ago :)
davidfiala commentedon Jan 9, 2025
Note to self: what I'm looking for is called
import elisionand is documented very nicely with caveats within typescript 5.0+verbatimModuleSyntaxflag.Discussed here per the earlier link: https://www.typescriptlang.org/tsconfig/#verbatimModuleSyntax
As a result, I'm renaming the issue to
--experimental-strip-types should elide imported types[-]--experimental-strip-types cannot import built in types: The requested module 'XXX' does not provide an export named 'YYY'[/-][+]--experimental-strip-types should elide imported types[/+]