About

This tool reduces a Haskell Buck project to its dependency graph skeleton for profiling purposes. The resulting project is a shallow list of directories, each corresponding to a Buck target in the original project, eliminating nested packages. Both targets and modules are given generic names lib Lib4Mod7, stripping each module down to its imports. Imports of modules from external dependencies are replaced with imports from a set of dummy packages named dep<N>, with N ranging from 1 through 100.

Implementation

The directory tests/tree1 contains an example test case consisting of a Buck project in the subdirectory original. These instructions write an intermediate JSON metadata tree in json and the final product in out.

1. Collect Haskell metadata in the original project:

   nix develop '.#parse' -c python parser.py --in 'tests/tree1/original' --out 'tests/tree1/json' local-packages src

   This replicates the original module tree, replacing each module with a JSON file containing only its module name and imports. The positional arguments allow restricting the subdirectories scanned for Haskell files.

2. Collect Buck metadata:

   buck uquery -B --output-format json "kind('haskell_library|export_file', deps('$target'))" > buck.json

   Substitute $target with the Buck target expression enumerating the desired targets. The simplest case would be //..., while the example in tests/tree1 uses //tests/tree1/original/.... Move the resulting buck.json to the root of the JSON tree created in the first step, e.g. tests/tree1/json/buck.json.

3. Run the transformer:

   nix run . -- --original 'tests/tree1/original' --json 'tests/tree1/json' --out 'tests/tree1/out'

   This program performs the following steps:

   • Parse the JSON files
   • Rename all targets to lib<L>
   • Resolve export_file labels
   • Rename all modules and matching imports
   • Replace the remaining imports by names like Dep<N>
   • Write the new structure to the output directory The example output tree will consist of four directories lib1, lib2, lib3, lib4, each containing one BUCK file with one target and Haskell files named Lib<L>Mod<M>.

4. Build the resulting project:

   nix develop '.#buck' -c buck build '//tests/tree1/out/...'

   The Nix environment provides the dummy dependencies dep1 ... dep100 used as external packages, as well as Buck and the appropriate GHC.