Repository: HiDeoo/starlight-links-validator (ts)

Issue:
More informative error for a specific typo
### Is your feature request related to a problem?

Hi, thanks for a great product! It saves a massive amount of time!

I made a typo and entered a link like the following: `[text](/https://astro.build/)`. The error log provided by the links validator didn't mention the page on which the problem was found. As a result, it was far more challenging to hunt down the bug.

Details: Whenever I prepend a / to the href of a link within a markdown or MDX file within Starlight, it breaks the build. The information given by the links validator includes only the phrase, "The URL must be of scheme file" and a stack trace. However, it includes no other information. Here's an example:
```
 validating links 
The URL must be of scheme file
  Stack trace:
    at new NodeError (node:internal/errors:406:5)
    at isValidAsset (C:/c/mono/node_modules/.pnpm/starlight-links-validator@0.7.1_@astrojs+starlight@0.24.2_astro@4.10.2_@types+node@20.14.2_ty_eyzihxfa7kaqghr2icuuqz2pdm/node_modules/starlight-links-validator/libs/validation.ts:154:42)
    at Module.validateLinks (C:/c/mono/node_modules/.pnpm/starlight-links-validator@0.7.1_@astrojs+starlight@0.24.2_astro@4.10.2_@types+node@20.14.2_ty_eyzihxfa7kaqghr2icuuqz2pdm/node_modules/starlight-links-validator/libs/validation.ts:55:9)      
    at runHookBuildDone (file:///C:/c/mono/node_modules/.pnpm/astro@4.10.2_@types+node@20.14.2_typescript@5.4.5/node_modules/astro/dist/integrations/hooks.js:409:58)
    at async AstroBuilder.build (file:///C:/c/mono/node_modules/.pnpm/astro@4.10.2_@types+node@20.14.2_typescript@5.4.5/node_modules/astro/dist/core/build/index.js:143:5)
 ELIFECYCLE  Command failed with exit code 1.
```

### Describe the solution you'd like

I'd like an error message that includes the file where the error was found. A line number or the text of the link would be nice if possible.

### Describe alternatives you've considered

I ended up solving it through a recursive process of deleting half the folders in the content directory to find the folder that the error was in, then following a similar process within the folder. Once I saw the actual link I immediately recognized it. If it happens again, I'd probably lean more heavily on git history.

### Additional Context

_No response_

Pull request description:
Fix a potential validation issue
Closes #44 

Patch:
diff --git a/packages/starlight-links-validator/libs/validation.ts b/packages/starlight-links-validator/libs/validation.ts
index 14cda25..a1754ab 100644
--- a/packages/starlight-links-validator/libs/validation.ts
+++ b/packages/starlight-links-validator/libs/validation.ts
@@ -205,9 +205,8 @@ function isValidAsset(path: string, context: ValidationContext) {
     }
   }
 
-  const filePath = fileURLToPath(new URL(path, context.outputDir))
-
   try {
+    const filePath = fileURLToPath(new URL(path, context.outputDir))
     const stats = statSync(filePath)
 
     return stats.isFile()


Test patch:
diff --git a/packages/starlight-links-validator/tests/basics.test.ts b/packages/starlight-links-validator/tests/basics.test.ts
index c2e8bbe..7a220ce 100644
--- a/packages/starlight-links-validator/tests/basics.test.ts
+++ b/packages/starlight-links-validator/tests/basics.test.ts
@@ -18,9 +18,10 @@ test('should not build with invalid links', async () => {
   try {
     await loadFixture('basics-invalid-links')
   } catch (error) {
-    expectValidationErrorCount(error, 28, 4)
+    expectValidationErrorCount(error, 29, 4)
 
     expectValidationErrors(error, 'test/', [
+      ['/https://starlight.astro.build/', ValidationErrorType.InvalidLink],
       ['/', ValidationErrorType.InvalidLink],
       ['/unknown', ValidationErrorType.InvalidLink],
       ['/unknown/', ValidationErrorType.InvalidLink],
diff --git a/packages/starlight-links-validator/tests/fixtures/basics-invalid-links/src/content/docs/test.md b/packages/starlight-links-validator/tests/fixtures/basics-invalid-links/src/content/docs/test.md
index b1afc42..6c63e25 100644
--- a/packages/starlight-links-validator/tests/fixtures/basics-invalid-links/src/content/docs/test.md
+++ b/packages/starlight-links-validator/tests/fixtures/basics-invalid-links/src/content/docs/test.md
@@ -6,6 +6,8 @@ title: Test
 
 - [External link](https://starlight.astro.build/)
 
+- [External link prefixed with a slash](/https://starlight.astro.build/)
+
 - [Home page](/)
 
 - [Unknown page](/unknown)