Static Syntax Validation for Code Generation with String Templates

Abstract

Many applications of model-based techniques ultimately require a model-to-text transformation to make practical use of the information encoded in meta-model instances. This step requires a code generator that has to be validated in order to ensure that the translation doesn’t alter the semantics of the model. Validation is often test-based, i.e. the code generator is executed on a wide range of inputs in order to verify the correctness of its output. Unfortunately, tests generally only prove the presence of errors, not their absence. This paper identifies the common core of string template implementations that are often used in the description of code generators, deriving a formal model that is suitable for mathematical reasoning. We provide a formal proof of the equivalence in expressiveness between string templates and context free grammars, thereby allowing the application of formal results from language theory. From there, we derive a scheme that would allow the verification of syntactical correctness for generated code before the translation of any model-instance is attempted, at the expense of freedom in the variability of the description.