When resolving references, the Ivy compiler has a few strategies it could use.
For relative path, one of strategies is [`RelativePathStrategy`](
https://github.com/angular/angular/blob/master/packages/compiler-cli/src/
ngtsc/imports/README.md#relativepathstrategy). This strategy
relies on `compilerOptions.rootDir` and `compilerOptions.rootDirs` to perform
the resolution, but language service only passes `rootDirs` to the compiler,
and not `rootDir`.
In reality, `rootDir` is very different from `rootDirs` even though they
sound the same.
According to the official [TS documentation][1],
> `rootDir` specifies the root directory of input files. Only use to control
> the output directory structure with --outDir.
> `rootDirs` is a list of root folders whose combined content represent the
> structure of the project at runtime. See [Module Resolution documentation](
> https://www.typescriptlang.org/docs/handbook/
> module-resolution.html#virtual-directories-with-rootdirs)
> for more details.
For now, we keep the behavior between compiler and language service consistent,
but we will revisit the notion of `rootDir` and how it is used later.
Fixangular/vscode-ng-language-service#1039
[1]: https://www.typescriptlang.org/docs/handbook/compiler-options.html
PR Close#40243
a62416c6e4