PLT-6271 Changed word splitting to initially split on any non-name character (#6261)

* PLT-6271 Changed word splitting to initially split on any non-name character

* Fixed detection of out of channel mentions

app/notification.go

@@ -665,8 +665,8 @@ func GetExplicitMentions(message string, keywords map[string][]string) (map[stri
 	message = removeCodeFromMessage(message)
 
 	for _, word := range strings.FieldsFunc(message, func(c rune) bool {
-		// Split on whitespace (as strings.Fields normally does) or on Markdown characters
-		return unicode.IsSpace(c) || c == '*' || c == '~'
+		// Split on any whitespace or punctuation that can't be part of an at mention
+		return !(c == '.' || c == '-' || c == '_' || c == '@' || unicode.IsLetter(c) || unicode.IsNumber(c))
 	}) {
 		isMention := false
 
@@ -694,11 +694,14 @@ func GetExplicitMentions(message string, keywords map[string][]string) (map[stri
 			isMention = true
 		}
 
-		if !isMention {
-			// No matches were found with the string split just on whitespace so try further splitting
-			// the message on punctuation
+		if isMention {
+			continue
+		}
+
+		if strings.ContainsAny(word, ".-") {
+			// This word contains a character that may be the end of a sentence, so split further
 			splitWords := strings.FieldsFunc(word, func(c rune) bool {
-				return model.SplitRunes[c]
+				return c == '.' || c == '-'
 			})
 
 			for _, splitWord := range splitWords {
@@ -727,6 +730,9 @@ func GetExplicitMentions(message string, keywords map[string][]string) (map[stri
 					potentialOthersMentioned = append(potentialOthersMentioned, username)
 				}
 			}
+		} else if _, ok := systemMentions[word]; !ok && strings.HasPrefix(word, "@") {
+			username := word[1:]
+			potentialOthersMentioned = append(potentialOthersMentioned, username)
 		}
 	}