This is a GHC plugin that detects and instruments overloaded function applications during compilation. At runtime, the instrumentation emits information about the overloaded calls whenever they are evaluated.
Important
This plugin relies on several unmerged features in GHC. Use this GHC branch for compatibility: https://gitlab.haskell.org/ghc/ghc/-/tree/wip/9.10-specialist-compat.
Add this plugin to build-depends and use -fplugin=GHC.Specialist on whatever
modules you wish to instrument. To set a dynamic sample rate for plugin output,
use -fplugin-opt=GHC.Specialist:f:N where N is the decimal probability of
output being emitted anytime instrumentation is executed. To set the plugin
verbosity use -fplugin-opt=GHC.Specialist:v for verbose and
-fplugin-opt=GHC.Specialist:vv for more verbose.
The test suite includes some basic unit tests. Each unit test consists of an
instrumented executable (see the test-TX executables in the cabal file). These
are included as build-tool-depends for the test suite, which executes the
executables and retrieves the specialist notes from the event log output.
Various conditions are then checked for each of the tests to ensure that the overloaded calls are what we expect and that the data included in the notes is accurate.
The test suite could be extended to check the function of the specialyze tool
more comprehensively or test the compile-time behavior of the plugin. At the
moment, it really only tests the generation and retrieval of the plugin output.