Add support for using on API and in browser

Previously, this plugin only worked on the CLI. This adds support
for usage on the API itself (invluding in browser environments).

index.js

@@ -1,25 +1,31 @@
 'use strict';
 
 var url = require('url');
-var fs = require('fs');
-var path = require('path');
 var propose = require('propose');
 var visit = require('unist-util-visit');
 var definitions = require('mdast-util-definitions');
 var hostedGitInfo = require('hosted-git-info');
 var urljoin = require('urljoin');
 var slug = require('remark-slug');
-var xtend = require('xtend');
+var xtend = require('xtend/mutable.js');
+
+/* Optional Node dependencies. */
+var fs;
+var path;
+
+try {
+  fs = require('fs');
+  path = require('path');
+} catch (err) {}
 
 module.exports = attacher;
 
 var referenceId = 'remarkValidateLinksReferences';
 var landmarkId = 'remarkValidateLinksLandmarks';
 var sourceId = 'remark-validate-links';
 
-completer.pluginId = sourceId;
+cliCompleter.pluginId = sourceId;
 
-var exists = fs.existsSync;
 var parse = url.parse;
 
 var viewPaths = {
@@ -39,14 +45,9 @@ function attacher(options, fileSet) {
   var info;
   var pack;
 
-  /* Throw when not on the CLI. */
-  if (!fileSet) {
-    throw new Error('remark-validate-links only works on the CLI');
-  }
-
   /* Try to get the repo from `package.json` when not
    * given. */
-  if (!repo) {
+  if (!repo && fs && fileSet) {
     try {
       pack = fileSet.files[0].cwd;
       pack = JSON.parse(fs.readFileSync(path.resolve(pack, 'package.json')));
@@ -67,21 +68,34 @@ function attacher(options, fileSet) {
     }
   }
 
-  /* Attach a `completer`. */
-  fileSet.use(completer);
-
   /* Attach `slug` and a plugin that adds our transformer after it. */
   this.use(slug).use(subplugin);
 
+  /* Attach a `completer`. */
+  if (fileSet) {
+    fileSet.use(cliCompleter);
+  } else {
+    this.use(apiCompleter);
+  }
+
   function subplugin() {
     /* Expose transformer. */
     return transformerFactory(fileSet, info);
   }
 }
 
-/* Completer. */
-function completer(set, done) {
+/* Completer for the API (one file, only headings are checked). */
+function apiCompleter() {
+  return transformer;
+  function transformer(tree, file) {
+    checkFactory(file.data[landmarkId])(file);
+  }
+}
+
+/* Completer for the CLI (multiple files, and support to add more). */
+function cliCompleter(set, done) {
   var exposed = {};
+  var check = checkFactory(exposed);
 
   set.valueOf().forEach(expose);
   set.valueOf().forEach(check);
@@ -92,10 +106,13 @@ function completer(set, done) {
     var landmarks = file.data[landmarkId];
 
     if (landmarks) {
-      exposed = xtend(exposed, landmarks);
+      xtend(exposed, landmarks);
     }
   }
+}
 
+function checkFactory(exposed) {
+  return check;
   function check(file) {
     /* istanbul ignore else - stdin */
     if (file.path) {
@@ -125,13 +142,14 @@ function transformerFactory(fileSet, info) {
       return;
     }
 
-    references = gatherReferences(file, ast, info);
+    references = gatherReferences(file, ast, info, fileSet);
     current = getPathname(filePath);
 
     for (link in references) {
       pathname = getPathname(link);
 
       if (
+        fileSet &&
         pathname !== current &&
         getHash(link) &&
         links.indexOf(pathname) === -1
@@ -182,8 +200,8 @@ function validate(exposed, file) {
      * for headings they are not added to remark. This
      * is especially useful because they might be
      * non-markdown files. Here we check if they exist. */
-    if ((real === undefined || real === null) && !hash) {
-      real = exists(reference);
+    if ((real === undefined || real === null) && !hash && fs) {
+      real = fs.existsSync(reference);
       references[reference] = real;
     }
 
@@ -214,16 +232,12 @@ function validate(exposed, file) {
 
 /* Gather references: a map of file-paths references
  * to be one or more nodes. */
-function gatherReferences(file, tree, info) {
+function gatherReferences(file, tree, info, fileSet) {
   var cache = {};
-  var filePath = file.path;
-  var dirname = file.dirname;
-  var getDefinition;
+  var getDefinition = definitions(tree);
   var prefix = '';
   var headingPrefix = '#';
 
-  getDefinition = definitions(tree);
-
   if (info && info.type in viewPaths) {
     prefix = '/' + info.path() + '/' + viewPaths[info.type] + '/';
   }
@@ -259,13 +273,18 @@ function gatherReferences(file, tree, info) {
 
     uri = parse(link);
 
+    if (!fileSet && (uri.hostname || uri.pathname)) {
+      return;
+    }
+
     if (!uri.hostname) {
       /* Handle hashes, or relative files. */
       if (!uri.pathname && uri.hash) {
-        link = filePath + uri.hash;
+        link = file.path + uri.hash;
         uri = parse(link);
       } else {
-        link = urljoin(dirname, link);
+        link = urljoin(file.dirname, link);
+
         if (uri.hash) {
           link += uri.hash;
         }
@@ -275,7 +294,7 @@ function gatherReferences(file, tree, info) {
 
     /* Handle full links. */
     if (uri.hostname) {
-      if (!prefix) {
+      if (!prefix || !fileSet) {
         return;
       }
 
@@ -315,6 +334,7 @@ function gatherReferences(file, tree, info) {
 
     if (hash) {
       link = pathname + '#' + hash;
+
       if (!cache[link]) {
         cache[link] = [];
       }

package.json

@@ -37,6 +37,7 @@
     "remark-preset-wooorm": "^3.0.0",
     "strip-ansi": "^4.0.0",
     "tape": "^4.0.0",
+    "to-vfile": "^2.1.2",
     "xo": "^0.18.0"
   },
   "scripts": {

readme.md

@@ -68,7 +68,46 @@ readme.md: no issues found
 
 ## Programmatic
 
-This plug-in is **not** available on the API of remark.
+> Note: The API only checks links to headings.  Other URLs are not checked.
+
+Say we have the following file, `example.md`:
+
+```markdown
+# Alpha
+
+This [exists](#alpha). This [exists][alpha] too.
+This [one does not](#does-not).
+
+# Bravo
+
+This is [not checked](readme.md#bravo).
+
+[alpha]: #alpha
+```
+
+And our script, `example.js`, looks as follows:
+
+```javascript
+var vfile = require('to-vfile');
+var report = require('vfile-reporter');
+var remark = require('remark');
+var links = require('remark-validate-links');
+
+remark()
+  .use(links)
+  .process(vfile.readSync('example.md'), function (err, file) {
+    console.error(report(err || file));
+  });
+```
+
+Now, running `node example` yields:
+
+```markdown
+example.md
+  4:6-4:31  warning  Link to unknown heading: `does-not`  remark-validate-links  remark-validate-links
+
+⚠ 1 warning
+```
 
 ## Configuration
 

test/index.js

@@ -4,6 +4,7 @@ var fs = require('fs');
 var path = require('path');
 var test = require('tape');
 var execa = require('execa');
+var vfile = require('to-vfile');
 var remark = require('remark');
 var strip = require('strip-ansi');
 var links = require('..');
@@ -21,13 +22,22 @@ var source = '  remark-validate-links  remark-validate-links';
 test('remark-validate-links', function (t) {
   t.plan(12);
 
-  t.throws(
-    function () {
-      remark().use(links).freeze();
-    },
-    /Error: remark-validate-links only works on the CLI/,
-    'should throw an error when not on the CLI'
-  );
+  t.test('should work on the API', function (st) {
+    st.plan(1);
+
+    remark()
+      .use(links)
+      .process(vfile.readSync('github.md'), function (err, file) {
+        st.deepEqual(
+          [err].concat(file.messages.map(String)),
+          [
+            null,
+            'github.md:5:37-5:51: Link to unknown heading: `world`'
+          ],
+          'should report messages'
+        );
+      });
+  });
 
   t.test('should throw on unparsable git repositories', function (st) {
     st.plan(1);