Use the same approach as for DAML, which re-uses the parsed AST.

From IRC:

<cocreature> alanz: our dlint integration takes the AST instead of reparsing the module which is a bit more efficient, see https://github.com/digital-asset/daml/blob/master/compiler/damlc/daml-ide-core/src/Development/IDE/Core/Rules/Daml.hs#L1081