feat(users/Profpatsch/haskell-module-deps): init

Three small helper functions that can display module graphs of haskell
projects.

Change-Id: I7395ffc8b025f4322efc6c1e494e6a6a0145342c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7675
Tested-by: BuildkiteCI
Autosubmit: Profpatsch <mail@profpatsch.de>
Reviewed-by: Profpatsch <mail@profpatsch.de>

users/Profpatsch/haskell-module-deps/default.nix

@@ -0,0 +1,55 @@
+{ depot, pkgs, lib, ... }:
+
+let
+  bins = depot.nix.getBins pkgs.zathura [ "zathura" ]
+    // depot.nix.getBins pkgs.haskellPackages.graphmod [ "graphmod" ]
+    // depot.nix.getBins pkgs.graphviz [ "dot" ]
+  ;
+
+  # Display a graph of all modules in a project and how they depend on each other.
+  # Takes the project directory as argument.
+  # Open in zathura.
+  haskell-module-deps = depot.nix.writeExecline "haskell-module-deps" { } [
+    "pipeline"
+    [ haskell-module-deps-with-filetype "pdf" "$@" ]
+    bins.zathura
+    "-"
+  ];
+
+  # Display a graph of all modules in a project and how they depend on each other.
+  # Takes the project directory as argument.
+  # Print a png to stdout.
+  haskell-module-deps-png = depot.nix.writeExecline "haskell-module-deps-png" { } [
+    haskell-module-deps-with-filetype
+    "png"
+    "$@"
+  ];
+
+  # Display a graph of all modules in a project and how they depend on each other.
+  # Takes the file type to generate as first argument
+  # and the project directory as second argument.
+  haskell-module-deps-with-filetype = pkgs.writers.writeBash "haskell-module-deps-with-filetype" ''
+    set -euo pipefail
+    shopt -s globstar
+    filetype="$1"
+    rootDir="$2"
+    ${bins.graphmod} \
+      ${/*silence warnings for missing external dependencies*/""} \
+      --quiet \
+      ${/*applies some kind of import simplification*/""} \
+      --prune-edges \
+      "$rootDir"/src/**/*.hs \
+      | ${bins.dot} \
+          ${/*otherwise it’s a bit cramped*/""} \
+          -Gsize="20,20!" \
+          -T"$filetype"
+  '';
+
+in
+depot.nix.readTree.drvTargets {
+  inherit
+    haskell-module-deps
+    haskell-module-deps-png
+    haskell-module-deps-with-filetype
+    ;
+}