Fix support for absolute paths on GitHub

At some point in time,
GitHub changed absolute paths in markdown,
to be related to the repo.
Instead of `github.com`.
This patch reflects that.

Closes GH-75.

lib/index.js

@@ -106,6 +106,8 @@
  *   Prefix of headings (example: `'#'`, `'#markdown-header-'`).
  * @property {string | null | undefined} [hostname]
  *   Domain of URLs (example: `'github.com'`, `'bitbucket.org'`).
+ * @property {boolean | null | undefined} [resolveAbsolutePathsInRepo]
+ *   Whether absolute paths (`/x/y/z.md`) resolve relative to a repo.
  * @property {boolean | null | undefined} [lines]
  *   Whether lines in files can be linked.
  * @property {string | null | undefined} [prefix]
@@ -227,6 +229,10 @@ export default function remarkValidateLinks(options, fileSet) {
             config.lines = lineLinks[info.type]
           }
 
+          if (info.type === 'github') {
+            config.resolveAbsolutePathsInRepo = true
+          }
+
           if (info.type in topAnchors) {
             config.topAnchor = topAnchors[info.type]
           }
@@ -416,9 +422,9 @@ export default function remarkValidateLinks(options, fileSet) {
             }
           }
 
-          // To do: test for no readme in directory.
+          // To do: test for no readme in folder.
 
-          // Else, there’s no readme that we can parse, so add the directory.
+          // Else, there’s no readme that we can parse, so add the folder.
           if (file) {
             filePath = path.join(filePath, file)
             statted.add(filePath)
@@ -632,14 +638,19 @@ function warn(landmarks, reference) {
  */
 // eslint-disable-next-line complexity
 function urlToPath(value, state, type) {
-  // Absolute paths: `/wooorm/test/blob/main/directory/example.md`.
+  // Absolute paths: `/folder/example.md`.
   if (value.charAt(0) === slash) {
     if (!state.urlConfig.hostname) {
       return
     }
 
+    const pathname =
+      state.urlConfig.resolveAbsolutePathsInRepo && state.urlConfig.prefix
+        ? state.urlConfig.prefix + 'main' + value
+        : value
+
     // Create a URL.
-    value = https + slashes + state.urlConfig.hostname + value
+    value = https + slashes + state.urlConfig.hostname + pathname
   }
 
   /** @type {URL | undefined} */
@@ -649,7 +660,7 @@ function urlToPath(value, state, type) {
     url = new URL(value)
   } catch {}
 
-  // URLs: `https://github.com/wooorm/test/blob/main/directory/example.md`.
+  // URLs: `https://github.com/wooorm/test/blob/main/folder/example.md`.
   if (url && state.root) {
     // Exit if we don’t have hosted Git info or this is not a URL to the repo.
     if (
@@ -666,7 +677,7 @@ function urlToPath(value, state, type) {
     value = url.pathname.slice(state.urlConfig.prefix.length)
 
     // Things get interesting here: branches: `foo/bar/baz` could be `baz` on
-    // the `foo/bar` branch, or, `baz` in the `bar` directory on the `foo`
+    // the `foo/bar` branch, or, `baz` in the `bar` folder on the `foo`
     // branch.
     // Currently, we’re ignoring this and just not supporting branches.
     value = value.split(slash).slice(1).join(slash)

readme.md

@@ -109,8 +109,8 @@ References w/o definitions are not checked: [delta]
 …and a module `example.js`:
 
 ```js
-import {remark} from 'remark'
 import remarkValidateLinks from 'remark-validate-links'
+import {remark} from 'remark'
 import {read} from 'to-vfile'
 import {reporter} from 'vfile-reporter'
 

test/fixtures/github.md

@@ -8,7 +8,7 @@ This is an invalid relative heading [link](#world).
 
 This is a valid relative file [link](https://github.com/wooorm/test/blob/main/examples/github.md).
 
-This is a valid absolute file [link](/wooorm/test/blob/main/examples/github.md).
+This is a valid absolute file [link](/examples/github.md).
 
 So is this [link](https://github.com/wooorm/test/blob/foo-bar/examples/github.md).
 
@@ -20,7 +20,7 @@ This is a valid external [file](../index.js).
 
 This is an invalid relative file [link](https://github.com/wooorm/test/blob/main/examples/world.md).
 
-This is an invalid absolute file [link](/wooorm/test/blob/main/examples/world.md).
+This is an invalid absolute file [link](/examples/world.md).
 
 So is this [link](https://github.com/wooorm/test/blob/foo-bar/examples/world.md).
 

test/fixtures/gitlab.md

@@ -12,6 +12,8 @@ So is this [link](https://gitlab.com/wooorm/test/blob/foo-bar/examples/gitlab.md
 
 And this [link](./examples/gitlab.md).
 
+How about this [link](/examples/gitlab.md).
+
 And this [link](examples/gitlab.md).
 
 This is a valid external [file](../index.js).