Changing baseUrl causes compiler not to look at @types subdirectory

[spion]

When baseUrl is set in tsconfig.json, the compiler will not look into baseUrl/@types to try and find type definitions

TypeScript Version: 2.2.1

Code

Example is available at:

https://github.com/spion/ts-base-url-issue

If the "paths" entry is removed from tsconfig.json, the compiler is unable to find react-dom

Expected behavior:

Compiles fine even without a "paths" entry.

Actual behavior:

Compiler doesn't find the definition file if the paths config option is removed. --trace-resolution shows that it never tries baseUrl/@types/react-dom

======== Resolving module 'react-dom' from '/Users/spion/Documents/tests/ts-modules-broken/app/index.ts'. ========
Explicitly specified module resolution kind: 'NodeJs'.
'baseUrl' option is set to '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules', using this value to resolve non-relative module name 'react-dom'
Resolving module name 'react-dom' relative to base url '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules' - '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom'.
Loading module as file / folder, candidate module location '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom', target file type 'TypeScript'.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom.ts' does not exist.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom.tsx' does not exist.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom.d.ts' does not exist.
Found 'package.json' at '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/package.json'.
'package.json' does not have a 'typings' field.
'package.json' does not have a 'types' field.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/index.ts' does not exist.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/index.tsx' does not exist.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/index.d.ts' does not exist.
Loading module 'react-dom' from 'node_modules' folder, target file type 'TypeScript'.
Directory '/Users/spion/Documents/tests/ts-modules-broken/app/node_modules' does not exist, skipping all lookups in it.
Directory '/Users/spion/Documents/tests/ts-modules-broken/node_modules' does not exist, skipping all lookups in it.
Directory '/Users/spion/Documents/tests/node_modules' does not exist, skipping all lookups in it.
Directory '/Users/spion/Documents/node_modules' does not exist, skipping all lookups in it.
Directory '/Users/spion/node_modules' does not exist, skipping all lookups in it.
Directory '/Users/node_modules' does not exist, skipping all lookups in it.
Directory '/node_modules' does not exist, skipping all lookups in it.
'baseUrl' option is set to '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules', using this value to resolve non-relative module name 'react-dom'
Resolving module name 'react-dom' relative to base url '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules' - '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom'.
Loading module as file / folder, candidate module location '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom', target file type 'JavaScript'.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom.js' does not exist.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom.jsx' does not exist.
Found 'package.json' at '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/package.json'.
'package.json' has 'main' field 'index.js' that references '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/index.js'.
File '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/index.js' exist - use it as a name resolution result.
======== Module name 'react-dom' was successfully resolved to '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/index.js'. ========
app/index.ts(1,22): error TS7016: Could not find a declaration file for module 'react-dom'. '/Users/spion/Documents/tests/ts-modules-broken/vendor/node_modules/react-dom/index.js' implicitly has an 'any' type.

Workaround

Adding a paths entry gets the @types directory into the lookup list again:

    "baseUrl": "./vendor/node_modules",
    "paths": {
      "*": ["@types/*", "*"]
    }

[mhegazy]

Setting baseUrl tells the compiler that all non-relative module names are under baseUrl, that also applies to your external dependencies like react-dom.

The path mapping you have added seems correct to me.

[spion]

@mhegazy in that case, it would be useful to add this to: https://www.typescriptlang.org/docs/handbook/module-resolution.html

Moving node_modules seems to be a common requirement, and changing only baseUrl doesn't work now that we have @types.

[mhegazy]

it currentlly states that:

Setting baseUrl informs the compiler where to find modules. All module imports with non-relative names are assumed to be relative to the baseUrl.

Not sure we need to state that @types\module is just another module.

[spion]

I believe a "moving node_modules" example would be worthwhile since its pretty common (watch mode in docker with external readonly filesystem, official rails webpacker typescript support using vendor/node_modules etc).

Its certainly not the most intuitive behaviour as people assume that baseUrl/node_modules and baseUrl/node_modules/@types are also looked up

I think it might save people an hour or two 😀

[ricklove]

@spion I agree. I thought baseUrl would be like defining the root of the directory (like where tsconfig.json is located.)

The 2 big surprises so far were that I had to point it to node_modules and that node_modules/@types was not found.