IsExternalLibraryImport

How we override isExternalLibraryImport

isExternalLibraryImport is a boolean returned by node's module resolver that is true if the target module is inside a node_modules directory.

This has 2x effects inside the compiler: a) compiler refuses to emit JS for external modules b) increments node_module depth +1, which affects maxNodeModulesJsDepth

If someone require()s a file inside node_modules, we need to override this flag to overcome (a).

ts-node's behavior

• If TS's normal resolution deems a file is external, we might override this flag.
  • Is file's containing module directory marked as "must be internal"?
    • if yes, override as "internal"
    • if no, track this flag, and leave it as "external"

When you try to require() a file that's previously been deemed "external", we mark the entire module's directory as "must be internal" and add the file to rootFiles to trigger a re-resolve.

When you try to require() a file that's totally unknown to the compiler, we have to add it to rootFiles to trigger a recompile. This is a separate issue.

Implementation notes

In updateMemoryCache:

• If file is not in rootFiles and is not known internal (either was never resolved or was resolved external)
  • mark module directory as "must be internal"
  • add file to rootFiles to either pull file into compilation or trigger re-resolve (will do both)

TODO: WHAT IF WE MUST MARK FILEA INTERNAL; WILL FILEB AUTOMATICALLY GET THE SAME TREATMENT?

TODO if noResolve, force adding to rootFileNames?

TODO if noResolve are the resolvers called anyway?

TODO eagerly classify .ts as internal, only use the "bucket" behavior for .js?

• b/c externalModule and maxNodeModulesJsDepth only seems to affect typechecking of .js, not .ts

Tests

require() .ts file where TS didn't know about it before require() .js file where TS didn't know about it before, w/allowJs import {} ./node_modules//.ts import {} ./node_modules//.js w/allowJs (initially external; will be switched to internal) import {} ./node_modules//.ts from another file within node_modules import {} ./node_modules//.js from another file within node_modules require() from ./node_modules when it is ignored; ensure is not forced internal and maxNodeModulesJsDepth is respected (type info does not change)

Keywords for searching TypeScript's source code

These may jog my memory the next time I need to read TypeScript's source and remember how this works.

currentNodeModulesDepth sourceFilesFoundSearchingNodeModules

isExternalLibraryImport is used to increment currentNodeModulesDepth currentNodeModulesDepth is used to put things into sourceFilesFoundSearchingNodeModules

https://github.com/microsoft/TypeScript/blob/ec338146166935069124572135119b57a3d2cd22/src/compiler/program.ts#L2384-L2398

getSourceFilesToEmit / sourceFileMayBeEmitted obeys internal "external" state, is responsible for preventing emit of external modules