Add improved errors

lib/index.js

@@ -134,6 +134,7 @@ import {nanoid} from 'nanoid'
 import {removePosition} from 'unist-util-remove-position'
 import {VFile} from 'vfile'
 import {findUp} from 'vfile-find-up'
+import {VFileMessage} from 'vfile-message'
 
 const exec = promisify(execCallback)
 
@@ -241,28 +242,20 @@ async function findPackage(from) {
 
   if (!file) return
 
-  let doc = ''
-
-  try {
-    doc = String(await fs.readFile(file.path))
-    /* c8 ignore next 7 -- verbose to test. */
-  } catch (error) {
-    // To do: improve error.
-    const exception = /** @type {NodeJS.ErrnoException} */ (error)
-    if (exception.code !== 'ENOENT') {
-      throw new Error('Could not read package: ' + exception)
-    }
-  }
+  const doc = String(await fs.readFile(file.path))
 
   /** @type {PackageJson} */
   let value
 
   try {
     value = JSON.parse(doc)
   } catch (error) {
-    // To do: improve error.
-    // Invalid JSON.
-    throw new Error('Could not parse package: ' + error)
+    const cause = /** @type {Error} */ (error)
+    throw new VFileMessage('Cannot parse `package.json` as JSON', {
+      cause,
+      ruleId: 'package-json-invalid',
+      source: 'remark-usage'
+    })
   }
 
   return {value, file}
@@ -279,8 +272,13 @@ async function findExample(cwd, givenExample) {
     : findImplicitExample(cwd)
 
   if (!example) {
-    // To do: improve error.
-    throw new Error('Could not find example')
+    throw new VFileMessage(
+      'Cannot find example file to use, either pass `options.example` or use a  name',
+      {
+        ruleId: 'example-missing',
+        source: 'remark-usage'
+      }
+    )
   }
 
   const url = new URL(example)
@@ -360,8 +358,12 @@ async function instrumentExample(cwd, options) {
       sourceType: 'unambiguous'
     })
   } catch (error) {
-    // To do: improve error.
-    throw new Error('Could not parse example: ' + error)
+    const cause = /** @type {Error} */ (error)
+    throw new VFileMessage('Cannot parse example as JS with Babel', {
+      cause,
+      ruleId: 'example-invalid-babel',
+      source: 'remark-usage'
+    })
   }
 
   let index = -1
@@ -486,7 +488,12 @@ async function run(example, instrumented, id) {
     const result = await exec([process.execPath, filePath].join(' '))
     stdout = result.stdout
   } catch (error) {
-    throw new Error('Could not run example: ' + error)
+    const cause = /** @type {Error} */ (error)
+    throw new VFileMessage('Cannot run example with Node', {
+      cause,
+      ruleId: 'example-invalid-node',
+      source: 'remark-usage'
+    })
   } finally {
     await fs.unlink(filePath)
   }

package.json

@@ -42,7 +42,8 @@
     "nanoid": "^5.0.0",
     "unist-util-remove-position": "^5.0.0",
     "vfile": "^6.0.0",
-    "vfile-find-up": "^7.0.0"
+    "vfile-find-up": "^7.0.0",
+    "vfile-message": "^4.0.0"
   },
   "devDependencies": {
     "@types/babel__core": "^7.0.0",

test/index.js

@@ -32,13 +32,10 @@ test('fixtures', async function (t) {
   const packageUrl = new URL('../package.json', import.meta.url)
   const packageBackUrl = new URL('../package.json.bak', import.meta.url)
   const brokenPackageUrl = new URL(
-    'fail-could-not-parse-package/package.json',
-    root
-  )
-  const brokenExampleUrl = new URL(
-    'fail-could-not-parse-example/example.js',
+    'fail-cannot-parse-package/package.json',
     root
   )
+  const brokenExampleUrl = new URL('fail-cannot-parse-example/example.js', root)
 
   await fs.writeFile(brokenExampleUrl, '"\n')
   await fs.writeFile(brokenPackageUrl, '{\n')
@@ -90,8 +87,7 @@ test('fixtures', async function (t) {
         }
 
         const message = folder.slice(5).replace(/-/g, ' ')
-        // .replace(/`/g, '')
-        assert.match(String(error), new RegExp(message, 'i'))
+        assert.match(String(error).replace(/`/g, ''), new RegExp(message, 'i'))
       }
     })
   }