@docusaurus/tsconfig: `baseUrl` is deprecated in TypeScript 6.0 (TS5101)

[mderazon]

Bug Description

@docusaurus/tsconfig sets "baseUrl": "." in its base config. Starting with TypeScript 6.0, baseUrl is deprecated and triggers a build error:

error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0.
Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.

This error surfaces in any Docusaurus project using TypeScript 6.x when running tsc --noEmit.

Root Cause

@docusaurus/tsconfig/tsconfig.json currently contains:

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "@site/*": ["./*"]
    }
  }
}

Per the TypeScript 6.0 migration guide, baseUrl was historically required to use paths, but this is no longer the case. The paths entries can simply be kept as-is without baseUrl, or baseUrl can be prepended to each entry.

Expected Behavior

tsc --noEmit passes without errors or deprecation warnings on TypeScript 6.x.

Workaround

Projects can add this to their own tsconfig.json to silence the warning:

{
  "extends": "@docusaurus/tsconfig",
  "compilerOptions": {
    "ignoreDeprecations": "6.0"
  }
}

Fix

Remove "baseUrl": "." from @docusaurus/tsconfig/tsconfig.json. The @site/* path alias should continue to work without it (TypeScript no longer requires baseUrl to be set when using paths).

[slorber]

I know about all this, see #11843

In v3.10 (released soon), our init templates will use "ignoreDeprecations": "6.0" by default and TS 6.0. Existing sites should add that manually if they want to use TS 6.0.

We can't do better for now. Removing baseUrl would be a breaking change so we can only do this in Docusaurus v4, and it's already planned.

Unfortunately, removing the baseUrl breaks the @site alias, see my comment here: #11843 (comment)

[slorber]

Fixed by #11915, scheduled for Docusaurus v4 (breaking change)