PLT-4454 Autolink anything that looks like an at mention (#4416)

* PLT-4454 Added autolinking for anything that looks like an at mention

* PLT-4454 Added unit tests for at mention autolinking

webapp/tests/formatting_at_mentions.test.jsx

@@ -0,0 +1,81 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+import assert from 'assert';
+
+import * as TextFormatting from 'utils/text_formatting.jsx';
+
+describe('TextFormatting.AtMentions', function() {
+    this.timeout(10000);
+
+    it('At mentions', function() {
+        assert.equal(
+            TextFormatting.autolinkAtMentions('@user', new Map(), {user: {}}),
+            'MM_ATMENTION0',
+            'should replace explicit mention with token'
+        );
+
+        assert.equal(
+            TextFormatting.autolinkAtMentions('abc"@user"def', new Map(), {user: {}}),
+            'abc"MM_ATMENTION0"def',
+            'should replace explicit mention surrounded by punctuation with token'
+        );
+
+        assert.equal(
+            TextFormatting.autolinkAtMentions('@user1 @user2', new Map(), {user1: {}, user2: {}}),
+            'MM_ATMENTION0 MM_ATMENTION1',
+            'should replace multiple explicit mentions with tokens'
+        );
+
+        assert.equal(
+            TextFormatting.autolinkAtMentions('@us_-e.r', new Map(), {'us_-e.r': {}}),
+            'MM_ATMENTION0',
+            'should replace multiple explicit mentions containing punctuation with token'
+        );
+
+        assert.equal(
+            TextFormatting.autolinkAtMentions('@us_-e.r', new Map(), {'us_-e.r': {}}),
+            'MM_ATMENTION0',
+            'should replace multiple explicit mentions containing valid punctuation with token'
+        );
+
+        assert.equal(
+            TextFormatting.autolinkAtMentions('@user.', new Map(), {user: {}}),
+            'MM_ATMENTION0.',
+            'should replace explicit mention followed by period with token'
+        );
+
+        assert.equal(
+            TextFormatting.autolinkAtMentions('@user.', new Map(), {'user.': {}}),
+            'MM_ATMENTION0',
+            'should replace explicit mention ending with period with token'
+        );
+    });
+
+    it('Implied at mentions', function() {
+        // PLT-4454 Assume users exist for things that look like at mentions until we support the new mention syntax
+        assert.equal(
+            TextFormatting.autolinkAtMentions('@user', new Map(), {}),
+            'MM_ATMENTION0',
+            'should imply user exists and replace mention with token'
+        );
+
+        assert.equal(
+            TextFormatting.autolinkAtMentions('@user.', new Map(), {}),
+            'MM_ATMENTION0.',
+            'should assume username doesn\'t end in punctuation'
+        );
+    });
+
+    it('Not at mentions', function() {
+        assert.equal(
+            TextFormatting.autolinkAtMentions('user@host', new Map(), {user: {}, host: {}}),
+            'user@host'
+        );
+
+        assert.equal(
+            TextFormatting.autolinkAtMentions('user@email.com', new Map(), {user: {}, email: {}}),
+            'user@email.com'
+        );
+    });
+});