NoFAQ: Synthesizing Command Repairs from Examples

Command-line tools are confusing and hard to use for novice programmers due to their cryptic error messages and lack of documentation. Novice users often resort to online help-forums for finding corrections to their buggy commands, but have a hard time in searching precisely for posts that are relevant to their problem and then applying the suggested solutions to their buggy command. We present a tool, NoFAQ, that uses a set of rules to suggest possible fixes when users write buggy commands that trigger commonly occurring errors. The rules are expressed in a language called FixIt and each rule pattern-matches against the user's buggy command and the corresponding error message, and uses these inputs to produce a possible fixed command. Our main contribution is an algorithm based on lazy VSA for synthesizing FixIt rules from examples of buggy and repaired commands. The algorithm allows users to add new rules in NoFAQ without having to manually encode them. We present the evaluation of NoFAQ on 92 benchmark problems and show that NoFAQ is able to instantly synthesize rules for 81 benchmark problems in real time using just 2 to 5 input-output examples for each rule.