Fix control character in definition destination

Closes GH-47

lib/handle/definition.js

@@ -24,8 +24,8 @@ export function definition(node, _, context) {
   if (
     // If there’s no url, or…
     !node.url ||
-    // If there’s whitespace, enclosed is prettier.
-    /[ \t\r\n]/.test(node.url)
+    // If there are control characters or whitespace.
+    /[\0- \u007F]/.test(node.url)
   ) {
     subexit = context.enter('destinationLiteral')
     value += '<' + safe(context, node.url, {before: '<', after: '>'}) + '>'

lib/util/format-link-as-autolink.js

@@ -28,7 +28,7 @@ export function formatLinkAsAutolink(node, context) {
       // And that starts w/ a protocol…
       /^[a-z][a-z+.-]+:/i.test(node.url) &&
       // And that doesn’t contain ASCII control codes (character escapes and
-      // references don’t work) or angle brackets…
+      // references don’t work), space, or angle brackets…
       !/[\0- <>\u007F]/.test(node.url)
   )
 }

test/index.js

@@ -931,6 +931,12 @@ test('definition', (t) => {
     'should encode a line ending in `url` in an enclosed url'
   )
 
+  t.equal(
+    to({type: 'definition', identifier: 'a', url: '\f'}),
+    '[a]: <\f>\n',
+    'should encode a line ending in `url` in an enclosed url'
+  )
+
   t.equal(
     to({type: 'definition', identifier: 'a', url: 'b(c'}),
     '[a]: b\\(c\n',
@@ -3646,8 +3652,8 @@ a *\\** is this emphasis? *\\**`
   tree = from(doc)
 
   t.deepEqual(
-    removePosition(tree, true),
     removePosition(from(to(tree)), true),
+    removePosition(tree, true),
     'should roundtrip asterisks (tree)'
   )
 
@@ -3679,20 +3685,20 @@ a _\\__ is this emphasis? _\\__`
   tree = from(doc)
 
   t.deepEqual(
-    removePosition(tree, true),
     removePosition(from(to(tree)), true),
+    removePosition(tree, true),
     'should roundtrip underscores (tree)'
   )
 
   doc = to(from(`(____`))
 
-  t.equal(doc, to(from(doc)), 'should roundtrip attention-like plain text')
+  t.equal(to(from(doc)), doc, 'should roundtrip attention-like plain text')
 
   doc = to(
     from('Once activated, a service worker ______, then transitions to idle…')
   )
 
-  t.equal(doc, to(from(doc)), 'should roundtrip faux “fill in the blank” spans')
+  t.equal(to(from(doc)), doc, 'should roundtrip faux “fill in the blank” spans')
 
   t.end()
 })