Report for runtime dependencies of a derivation

default.nix

# MIT License, see below
#
# These are some helpers for figuring out the derivations attributes of runtime
# dependencies of a derivation, in particular the function `runtimeReport`. At
# the bottom of the file you can see it used on `hello`. Spoiler: glibc is a
# runtime dependency.
# For more info see
#
#   https://nmattia.com/posts/2019-10-08-runtime-dependencies.html

# Let's call these "imports". They're functions used throughout the code.
# Nothing interesting here.
with rec
  { pkgs = import <nixpkgs> {};
    inherit (pkgs)
      closureInfo
      runCommandNoCC
      writeText
      jq
      ;
    inherit (pkgs.lib)
      concatLists
      concatMap
      concatStringsSep
      filter
      isAttrs
      isDerivation
      isList
      isString
      mapAttrsToList
      ;
    inherit (builtins)
      genericClosure
      hasAttr
      toJSON
      typeOf
      unsafeDiscardStringContext
      ;
  };

let

# Create a "runtime report" of the runtime dependencies of `drv`. A "runtime
# report" is made up of smaller "dependency reports". A "dependency report" is
# a string describing the dependency, made from the dependency's derivation
# attributes. Here we use `mkReport` to make the report of any particular
# dependency.
#
# NOTE: we use the following terms:
#
#   * "buildtime" to mean basically any derivation involved in the build of
#     `drv`.
#   * "buildtime-only" for the "buildtime" dependencies that _are not_
#     referenced anymore by `drv`'s store entry.
#   * "runtime" for the rest.
#
# The "runtime report" is created in two steps:
#
#   * Generate reports for all the _buildtime_ dependencies with
#     `buildtimeReports`.
#   * Filter out the reports for buildtime-only dependencies.
#
# Most of the "buildtime" reports won't even be used, because most buildtime
# dependencies are buildtime-only dependencies. However Nix does not give us a
# way of retrieving the derivation attributes of runtime dependencies, but we
# can twist its arm to:
#
#   * Give us the store paths of runtime dependencies (see `cinfo`).
#   * Give us the derivation attributes of all the buildtime dependencies (see
#     `buildtimeDerivations`).
#
# Here's the hack: `buildtimeReports` tags the reports with the (expected)
# store path of the "buildtime" dependency, which we cross check against the
# list of runtime store paths. If it's a match, we keep it. Otherwise, we
# discard it.
runtimeReport = drv:
  runCommandNoCC "${drv.name}-report" { buildInputs = [ jq ]; }
  # XXX: This is to avoid IFD
  ''
    (
      echo "  ---------------------------------"
      echo "  |        OFFICIAL REPORT        |"
      echo "  |   requested by: the lawyers   |"
      echo "  |    written by: yours truly    |"
      echo "  |    TOP SECRET - TOP SECRET    |"
      echo "  ---------------------------------"
      echo
      echo "runtime dependencies of ${drv.name}:"
      cat ${buildtimeReports drv} |\
        jq -r --slurpfile runtime ${cinfo drv} \
          ' # First, we strip away (path-)duplicates.
            unique_by(.path)
            # Then we map over each build-time derivation and use `select()`
            # to keep only the ones that show up in $runtime

          | map(    # this little beauty checks if "obj.path" is in "runtime"
                select(. as $obj | $runtime | any(.[] | . == $obj.path))
              | .report)
          | .[]'
    ) > $out
  '';

# Creates reports for all of `drv`'s buildtime dependencies. Each element in
# the list has two fields:
#
#   * path = "/nix/store/..."
#   * report = "some report based on the dependency's derivation attributes"
buildtimeReports = drv: writeText "${drv.name}-runtime" ( toJSON (
  map (obj:
    # unsafe: optimization to avoid downloading unused deps
    { # XXX: we discard the context of the dependencies' store paths because
      # they're only ever used for lookup. This matters when fetching a
      # prebuilt final report -- there's no point downloading all of `drv`'s
      # buildtime dependencies.
      path = unsafeDiscardStringContext obj.key;
      report = mkReport obj.drv;
    }
  )
  (buildtimeDerivations drv) # the heavy lifting is done somewhere else
  ));

# Returns a list of all of `drv0`'s inputs, a.k.a. buildtime dependencies.
# Elements in the list has two fields:
#
#  * key: the store path of the input.
#  * drv: the actual derivation object.
#
# There are no guarantees that this will find _all_ inputs, but it works well
# enough in practice.
#
buildtimeDerivations = drv0:
  let
    # We include all the outputs because they each have different outPaths
    drvOutputs = drv:
      # XXX: some derivations, like stdenv, don't have "outputs"
      if hasAttr "outputs" drv
      then map (output: drv.${output}) drv.outputs
      else [ drv ];

    # Recurse into the derivation attributes to find new derivations
    drvDeps = attrs:
        mapAttrsToList (k: v:
        if isDerivation v then (drvOutputs v)
        else if isList v
          then concatMap drvOutputs (filter isDerivation v)
        else []
        ) attrs;
  in
    # Walk through the whole DAG of dependencies, using the `outPath` as an
    # index for the elements.
    let wrap = drv: { key = drv.outPath ; inherit drv; }; in genericClosure
    { startSet = map wrap (drvOutputs drv0) ;
      operator = obj: map wrap
        ( concatLists (drvDeps obj.drv.drvAttrs) ) ;
    };

# make a report. Would could also output a json object and process everything
# later on.
mkReport = drv:
  let
    license =
      if hasAttr "meta" drv && hasAttr "license" drv.meta then
        if isList drv.meta.license then
          concatStringsSep ", " (
            map renderLicense drv.meta.license)
        else renderLicense drv.meta.license
      else "no license";

    maintainer =
      if hasAttr "meta" drv && hasAttr "maintainers" drv.meta
      then concatStringsSep ", " (map (m: m.name) drv.meta.maintainers)
      else "nobody";

  in " - ${drv.name} (${license}) maintained by ${maintainer}";

# Basically pretty prints a license
renderLicense = license:
  if isAttrs license then license.shortName
  else if isString license then license
  else abort "no idea how to handle license of type ${typeOf license}";

# This is a wrapper around nixpkgs' `closureInfo`. It produces a JSON file
# containing a list of the store paths of `drv`'s runtime dependencies.
cinfo = drv: runCommandNoCC "${drv.name}-cinfo"
  { buildInputs = [ jq ]; }
  # NOTE: we avoid IFD here as well
  ''
    cat ${closureInfo { rootPaths = [ drv ]; }}/store-paths |\
      grep -v "^$" |\
      jq -R -s -c 'split("\n")' |\
      jq -c 'map(select( length > 0 ))' > $out
  '';

in runtimeReport pkgs.hello

# MIT License
#
# Copyright (c) 2021 Nicolas Mattia
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
#

Is it possible to extend this to also do things like:

1. Get a report on all dependencies in the closure.
2. Get a report on only build dependencies (non-runtime dependencies)
3. Get a report only on immediate dependencies?
4. Dependencies that our "program" links to vs packages that only contain executables.

Also what does your XXX mean here? What are you using this notation for in your comments?

1. What do you mean of all dependencies? Build time + runtime?
2. Yes, that's what buildTimeReports does (although maybe you want to filter out the runtime ones?)
3. Yes, should be straightforward. Instead of traversing the entire DAG, stop at 1-hop from the root.
4. It's a heads up

Hope that helps!

Dependencies of the entire closure. But I realized you already do that. So only the immediate dependencies means stopping 1 hop from the root.

Right so what about running buildTimeReports and filtering out all the runtime ones...

Could this be turned into an opensource program that we package into nixpkgs? It would be really useful. It could also produce JSON for further analysis.

drvDeps does not find almost all deps because it is not searching in strings for nix store paths and similar. I couldn't find anything like nix derivation show from inside nix without recursive nix, so not sure how to fix that and find all the tings.