Typescript config support

[jesusbotella]

Which issue, if any, is this issue related to?

Closes #4940.

Is there anything in the PR that needs further explanation?

I think it is self-explanatory, but I have two doubts:

• Don't know where to add some more documentation about TypeScript config files (e.g., how to be able to export CommonJS for stylelint if you have another export format already, and some other issues that may appear)
• Are there any tests for configuration files? I would like to add one for TypeScript

[vankop]

Are there any tests for configuration files? I would like to add one for TypeScript

Maybe system tests will help you
https://github.com/stylelint/stylelint/tree/master/system-tests

[ota-meshi]

Does this change require users to install "typescript" due to "peerDependencies" of "ts-node"?

[ota-meshi]

I think we need to add "typescript" to "dependencies" to not require the user to install it.

[hudochenkov]

Does this change require users to install "typescript" due to "peerDependencies" of "ts-node"?
I think we need to add "typescript" to "dependencies" to not require the user to install it.

Installing TypeScript for 99.999% of users, who don't need it is bad. Also showing peer dependency warning about it. We need different solution, probably.

[ybiquitous]

I agree with @ota-meshi and @hudochenkov. So, I suggest another solution as follows:

• Dynamic require @endemolshinegroup/cosmiconfig-typescript-loader. The typescriptLoader() function is called only when a user has own stylelint.config.ts file.
• Move @endemolshinegroup/cosmiconfig-typescript-loader from dependencies to peerDependencies.
• Add the peerDependenciesMeta field in order to suppress an installation warning such as:

  npm WARN stylelint@13.7.0 requires a peer of @endemolshinegroup/cosmiconfig-typescript-loader@>=3.0.2 but none is installed. You must install peer dependencies yourself.

diff --git a/lib/createStylelint.js b/lib/createStylelint.js
index 3d0b17aa..39a6c438 100644
--- a/lib/createStylelint.js
+++ b/lib/createStylelint.js
@@ -8,9 +8,13 @@ const getPostcssResult = require('./getPostcssResult');
 const isPathIgnored = require('./isPathIgnored');
 const lintSource = require('./lintSource');
 const path = require('path');
-const typescriptLoader = require('@endemolshinegroup/cosmiconfig-typescript-loader').default;
 const { cosmiconfig } = require('cosmiconfig');
 
+const typescriptLoader = (...args) => {
+	const loader = require('@endemolshinegroup/cosmiconfig-typescript-loader').default;
+	return loader(...args);
+}
+
 const IS_TEST = process.env.NODE_ENV === 'test';
 const STOP_DIR = IS_TEST ? path.resolve(__dirname, '..') : undefined;
 
diff --git a/package.json b/package.json
index 841913d6..7510b222 100644
--- a/package.json
+++ b/package.json
@@ -110,7 +110,6 @@
     ]
   },
   "dependencies": {
-    "@endemolshinegroup/cosmiconfig-typescript-loader": "^3.0.2",
     "@stylelint/postcss-css-in-js": "^0.37.2",
     "@stylelint/postcss-markdown": "^0.36.1",
     "autoprefixer": "^9.8.6",
@@ -161,6 +160,7 @@
     "write-file-atomic": "^3.0.3"
   },
   "devDependencies": {
+    "@endemolshinegroup/cosmiconfig-typescript-loader": "^3.0.2",
     "@stylelint/prettier-config": "^2.0.0",
     "@stylelint/remark-preset": "^1.0.0",
     "@types/balanced-match": "^1.0.1",
@@ -196,6 +196,14 @@
     "remark-cli": "^8.0.1",
     "typescript": "^3.9.6"
   },
+  "peerDependencies": {
+    "@endemolshinegroup/cosmiconfig-typescript-loader": ">=3.0.2"
+  },
+  "peerDependenciesMeta": {
+    "@endemolshinegroup/cosmiconfig-typescript-loader": {
+      "optional": true
+    }
+  },
   "engines": {
     "node": ">=10.13.0"
   }

[jesusbotella]

Thank you for your comment @ybiquitous! I have just pushed the changes, but it seems like I need to work on this a little more because some checks are failing.

[ybiquitous]

@jesusbotella I think the following ways can resolve the errors:

Rest parameter 'args' implicitly has an 'any[]' type.

Explicitly set the missing types as follows:

--- a/lib/createStylelint.js
+++ b/lib/createStylelint.js
@@ -10,10 +10,14 @@ const lintSource = require('./lintSource');
 const path = require('path');
 const { cosmiconfig } = require('cosmiconfig');
 
-const typescriptLoader = (...args) => {
+/**
+ * @param {string} filepath
+ * @param {string} content
+ */
+const typescriptLoader = (filepath, content) => {
 	const loader = require('@endemolshinegroup/cosmiconfig-typescript-loader').default;
 
-	return loader(...args);
+	return loader(filepath, content);
 };
 
 const IS_TEST = process.env.NODE_ENV === 'test';

Cannot find module '@endemolshinegroup/cosmiconfig-typescript-loader' or its corresponding type declarations.

Add the package also to devDependencies:

--- a/package.json
+++ b/package.json
@@ -160,6 +160,7 @@
     "write-file-atomic": "^3.0.3"
   },
   "devDependencies": {
+    "@endemolshinegroup/cosmiconfig-typescript-loader": "^3.0.2",
     "@stylelint/prettier-config": "^2.0.0",
     "@stylelint/remark-preset": "^1.0.0",
     "@types/balanced-match": "^1.0.1",

[jeddy3]

Closing following discussion in #4940 and solution prorposed in #4940 (comment)