fix: mentions rendered incorrectly - WPB-21687

wire-ios/Wire-iOS Tests/ConversationCell/TextMessageMentionsTests.swift

@@ -172,4 +172,30 @@
         let mention = Mention(range: NSRange(location: 0, length: 8), user: selfUser)
         verify(message: createMessage(messageText: messageText, mentions: [mention]))
     }
+
+    func testThatItHandlesMalformedMentionRange_MissingAtSymbol() {
+        // Test case for the bug where another app incorrectly sends a mention range
+        // that starts one character after the '@' symbol (e.g., location: 7 instead of 6)
+        // This should be automatically corrected to include the '@'
+        let messageText = "Hello @Bruno! How are you?"
+
+        // Malformed range: starts at 'B' (index 7) instead of '@' (index 6)
+        let malformedMention = Mention(range: NSRange(location: 7, length: 5), user: otherUser)
+
+        // The fix should automatically adjust this to location: 6, length: 6
+        // and render correctly as "@Bruno" instead of "@@runo"
+        verify(message: createMessage(messageText: messageText, mentions: [malformedMention]))
+    }
+
+    func testThatItHandlesMultipleMentionsWithOneMalformed() {
+        let messageText = "Hey @Bruno and @Me, let's meet!"
+
+        // First mention is malformed (starts at 'B' instead of '@')
+        let malformedMention = Mention(range: NSRange(location: 5, length: 5), user: otherUser)
+
+        // Second mention is correct
+        let correctMention = Mention(range: NSRange(location: 15, length: 3), user: selfUser)
+
+        verify(message: createMessage(messageText: messageText, mentions: [malformedMention, correctMention]))
+    }
 }

wire-ios/Wire-iOS/Sources/UserInterface/Conversation/Content/Cells/Utility/NSAttributedString+MessageFormatting.swift

@@ -22,6 +22,7 @@ import WireDataModel
 import WireDesign
 import WireFoundation
 import WireLinkPreview
+import WireLogging
 import WireUtilities
 
 extension NSAttributedString {
@@ -245,14 +246,57 @@ private extension String {
     mutating func replaceMentionsWithTextMarkers(mentions: [Mention]) -> [TextMarker<Mention>] {
         mentions.sorted(by: {
             $0.range.location > $1.range.location
-        }).compactMap { mention in
-            guard let range = Range(mention.range, in: self) else { return nil }
-
-            let name = String(self[range].dropFirst()) // drop @
-            let textObject = TextMarker<Mention>(mention, replacementText: name)
-
+        }).compactMap { mention -> TextMarker<Mention>? in
+            // All mentions are expected to have a @ prefix and the range
+            // of the mention should include this prefix (and not just the
+            // name). Eg "Hello @bob" should have a mention range of
+            // NSRange(location: 6, length: 4). If it doesn't, it will
+            // be rendered incorrectly.
+            //
+            // But we suspect in some cases the sender might be only
+            // specifying a mention range that covers the name and not
+            // the @ prefix (i.e NSRange(location: 7, length: 3)).
+            //
+            // To handle this case, we check if the range includes the @
+            // and if it doesn't adjust the range so that it does.
+            var adjustedRange = mention.range
+
+            if adjustedRange.location > 0, adjustedRange.location < utf16.count {
+                let utf16View = self.utf16
+                let charIndex = utf16View.index(utf16View.startIndex, offsetBy: adjustedRange.location)
+
+                if charIndex < utf16View.endIndex {
+                    let charAtLocation = utf16View[charIndex]
+
+                    // If the range doesn't start with '@', check if the character before does
+                    if charAtLocation != 64 { // '@' in UTF-16
+                        let prevIndex = utf16View.index(before: charIndex)
+                        if prevIndex >= utf16View.startIndex, utf16View[prevIndex] == 64 {
+                            // Adjust range to include the '@'
+                            adjustedRange.location -= 1
+                            adjustedRange.length += 1
+                        }
+                    }
+                }
+            }
+
+            guard let range = Range(adjustedRange, in: self) else { return nil }
+            let name = String(self[range])
+
+            // Final validation: ensure the extracted name starts with '@'
+            guard name.hasPrefix("@") else {
+                WireLogger.messaging.error("Mention range does not start with '@': \(mention.range), text: '\(name)'")
+                return nil
+            }
+
+            // Create a corrected mention with the adjusted range
+            let correctedMention = Mention(range: adjustedRange, user: mention.user)
+
+            // Strip the '@' from the name since the mention rendering code adds it back
+            let nameWithoutAt = name.hasPrefix("@") ? String(name.dropFirst()) : name
+
+            let textObject = TextMarker<Mention>(correctedMention, replacementText: nameWithoutAt)
             replaceSubrange(range, with: textObject.token)
-
             return textObject
         }
     }