Types from `*.d.ts` files are not parsed in node_modules

[rvetere]

If an installed package would deliver type informations with d.ts files, it won't parse these files and interface informations are missing in the props.

It could be fixed in the makeFsImporter.ts file with a simple addition:

if (!nextFile) {
      // Customization: try to read from a "d.ts" file instead, if it exists
      if (resolvedSource.includes("node_modules")) {
        const dtsPath = resolvedSource.replace(".js", ".d.ts");
        if (fs.existsSync(dtsPath)) {
          resolvedSource = dtsPath;
        }
      }
      // Customization: end

      // Read and parse the code
      const src = fs.readFileSync(resolvedSource, "utf8");

      nextFile = file.parse(src, resolvedSource);

      parseCache.set(resolvedSource, nextFile);
}

But i didn't want to make another pull request because i'm not sure if this is a nice way to solve it.

[alirezamirian]

There are currently two issues with types that are imported from .d.ts files:

1. import resolution: resolve that's used in the built-in fs importer is not built to locate type declaration files. Simply replacing .js with .d.ts is not a reliable solution, as it's quite likely for the type declaration file to be named something else, which is then specified in types or typings key of the package.json file. To make the matters worse, many packages have started to use package.json exports, which can include a types mapping too (example).
2. Parsing: The parsing doesn't always work for .d.ts files, since it doesn't recognize declare syntax. It's also reported in Can be generated from a difinition file? #814 (comment) and Typescript: Component declaration reference is not recognized by parser #898.

With an increasing number of reusable hooks and headless components, it is becoming common for component libraries to extend prop interfaces exported from third-party packages. Looking forward to improvements in this area, and I could also look into possible solutions for the first point.

Also related: #416, #352, storybookjs/storybook#10034