Large software companies need customized tools to manage their source code. These tools are often built in an ad-hoc fashion, using brittle technologies such as regular expressions and home-grown parsers. Changes in the language cause the tools to break. More importantly, these ad-hoc tools often do not support uncommon-but-valid code code patterns. We report our experiences building source-code analysis tools at Google on top of a third-party, open-source, extensible compiler. We describe

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... tools in use on our Java codebase. The first, Strict Java Dependencies, enforces our dependency policy in order to reduce JAR file sizes and testing load. The second, error-prone, adds new error checks to the compilation process and automates repair of those errors at a wholecodebase scale. The third, Thindex, reduces the indexing burden for a Java IDE so that it can support Google-sized projects.