How to find similar meaning log messages in the source code?
A simple idea, non-supervision:
 1.Stemming, reduceing punctuations. Then you can use Bag of word with TF-IDF to represent the log sentences. 


Run K-means to cluster your sentences. If your sentences are belong to 
5 type. You can set K=5.


Of course, you can use Regular Express to classify those sentences.