buildDotnetModule: make fetch-deps find output path automatically

doc/languages-frameworks/dotnet.section.md

···
 * `dotnetPackFlags` can be used to pass flags to `dotnet pack`. Used only if `packNupkg` is set to `true`.
 * `dotnetFlags` can be used to pass flags to all of the above phases.
 
-When packaging a new application, you need to fetch its dependencies. You can run `nix-build -A package.fetch-deps` to generate a script that will build a lockfile for you. After running the script you should have the location of the generated lockfile printed to the console, which can be copied to a stable directory. Then set `nugetDeps = ./deps.nix` and you're ready to build the derivation.
+When packaging a new application, you need to fetch its dependencies. Create an empty `deps.nix`, set `nugetDeps = ./deps.nix`, then run `nix-build -A package.fetch-deps` to generate a script that will build the lockfile for you.
 
 Here is an example `default.nix`, using some of the previously discussed arguments:
 ```nix

maintainers/scripts/update-dotnet-lockfiles.nix

···
+/*
+  To run:
+
+      nix-shell maintainers/scripts/update-dotnet-lockfiles.nix
+
+  This script finds all the derivations in nixpkgs that have a 'fetch-deps'
+  attribute, and runs all of them sequentially. This is useful to test changes
+  to 'fetch-deps', 'nuget-to-nix', or other changes to the dotnet build
+  infrastructure. Regular updates should be done through the individual packages
+  update scripts.
+ */
+let
+  pkgs = import ../.. {};
+
+  inherit (pkgs) lib;
+
+  packagesWith = cond: pkgs:
+    let
+      packagesWithInner = attrs:
+        lib.unique (
+          lib.concatLists (
+            lib.mapAttrsToList (name: elem:
+              let
+                result = builtins.tryEval elem;
+              in
+                if result.success then
+                  let
+                    value = result.value;
+                  in
+                    if lib.isDerivation value then
+                      lib.optional (cond value) value
+                    else
+                      if lib.isAttrs value && (value.recurseForDerivations or false || value.recurseForRelease or false) then
+                        packagesWithInner value
+                      else []
+                else []) attrs));
+    in
+      packagesWithInner pkgs;
+
+  packages =
+    packagesWith (pkgs: pkgs ? fetch-deps) pkgs;
+
+  helpText = ''
+    Please run:
+
+        % nix-shell maintainers/scripts/update-dotnet-lockfiles.nix
+  '';
+
+  fetchScripts = map (p: p.fetch-deps) packages;
+
+in pkgs.stdenv.mkDerivation {
+  name = "nixpkgs-update-dotnet-lockfiles";
+  buildCommand = ''
+    echo ""
+    echo "----------------------------------------------------------------"
+    echo ""
+    echo "Not possible to update packages using \`nix-build\`"
+    echo ""
+    echo "${helpText}"
+    echo "----------------------------------------------------------------"
+    exit 1
+  '';
+  shellHook = ''
+    unset shellHook # do not contaminate nested shells
+    set -e
+    for x in $fetchScripts; do
+      $x
+    done
+    exit
+  '';
+  inherit fetchScripts;
+}

pkgs/applications/blockchains/nbxplorer/util/update-common.sh

···
 trap 'echo "Error at ${BASH_SOURCE[0]}:$LINENO"' ERR
 
 pkgName=$1
-depsFile=$2
 
 : ${getVersionFromTags:=}
 : ${refetch:=}
···
 if [[ $newVersion == $oldVersion && ! $refetch ]]; then
   echo "nixpkgs already has the latest version $newVersion"
   echo "Run this script with env var refetch=1 to re-verify the content hash via GPG"
-  echo "and to recreate $(basename "$depsFile"). This is useful for reviewing a version update."
+  echo "and to recreate deps.nix. This is useful for reviewing a version update."
   exit 0
 fi
 
···
 echo
 
 # Create deps file
-$(nix-build "$nixpkgs" -A $pkgName.fetch-deps --no-out-link) "$depsFile"
+$(nix-build "$nixpkgs" -A $pkgName.fetch-deps --no-out-link)

pkgs/applications/emulators/ryujinx/updater.sh

···
 set -euo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-DEPS_FILE="$(realpath "./deps.nix")"
-
 # provide a github token so you don't get rate limited
 # if you use gh cli you can use:
 #     `export GITHUB_TOKEN="$(cat ~/.config/gh/config.yml | yq '.hosts."github.com".oauth_token' -r)"`
···
 
 echo "building Nuget lockfile"
 
-$(nix-build -A ryujinx.fetch-deps --no-out-link) "$DEPS_FILE"
+$(nix-build -A ryujinx.fetch-deps --no-out-link)

pkgs/applications/graphics/pinta/default.nix

···
   # How-to update deps:
   # $ nix-build -A pinta.fetch-deps
   # $ ./result
-  # $ cp /tmp/Pinta-deps.nix ./pkgs/applications/graphics/pinta/deps.nix
   # TODO: create update script
   nugetDeps = ./deps.nix;
 

pkgs/applications/misc/ArchiSteamFarm/update.sh

···
 set -euo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-deps_file="$(realpath ./deps.nix)"
-
 new_version="$(curl ${GITHUB_TOKEN:+" -u \":$GITHUB_TOKEN\""} -s "https://api.github.com/repos/JustArchiNET/ArchiSteamFarm/releases" | jq -r  'map(select(.prerelease == false)) | .[0].tag_name')"
 old_version="$(sed -nE 's/\s*version = "(.*)".*/\1/p' ./default.nix)"
 
···
     update-source-version ArchiSteamFarm "$new_version"
 fi
 
-$(nix-build -A ArchiSteamFarm.fetch-deps --no-out-link) "$deps_file"
+$(nix-build -A ArchiSteamFarm.fetch-deps --no-out-link)
 
 popd
 "$asf_path/web-ui/update.sh"

pkgs/applications/version-management/git-credential-manager/update.sh

···
 sed -i -Ee "s/hash = \"sha256-[A-Za-z0-9=]{44}\"/hash = \"${hash}\"/" default.nix
 
 
-nugetDeps="$(realpath ./deps.nix)"
-$(nix-build ../../../.. -A git-credential-manager.fetch-deps --no-out-link) "$nugetDeps"
+$(nix-build ../../../.. -A git-credential-manager.fetch-deps --no-out-link)

pkgs/development/tools/continuous-integration/github-runner/update.sh

···
 fi
 
 update-source-version github-runner "$latestVersion"
-$(nix-build -A github-runner.fetch-deps --no-out-link) "$(dirname "$BASH_SOURCE")/deps.nix"
+$(nix-build -A github-runner.fetch-deps --no-out-link)
 

pkgs/development/tools/marksman/update.sh

···
 
 update-source-version marksman "$version"
 
-$(nix-build -A marksman.fetch-deps --no-out-link) "$(dirname -- "${BASH_SOURCE[0]}")/deps.nix"
+$(nix-build -A marksman.fetch-deps --no-out-link)

pkgs/development/tools/omnisharp-roslyn/updater.sh

···
 
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-deps_file="$(realpath "./deps.nix")"
-
 new_version="$(curl -s "https://api.github.com/repos/OmniSharp/omnisharp-roslyn/releases?per_page=1" | jq -r '.[0].name')"
 old_version="$(sed -nE 's/\s*version = "(.*)".*/\1/p' ./default.nix)"
 
···
 cd ../../../..
 update-source-version omnisharp-roslyn "${new_version//v}"
 
-$(nix-build -A omnisharp-roslyn.fetch-deps --no-out-link) "$deps_file"
+$(nix-build -A omnisharp-roslyn.fetch-deps --no-out-link)

pkgs/games/osu-lazer/update.sh

···
 set -eo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-deps_file="$(realpath "./deps.nix")"
-
 new_version="$(curl -s "https://api.github.com/repos/ppy/osu/releases?per_page=1" | jq -r '.[0].name')"
 old_version="$(sed -nE 's/\s*version = "(.*)".*/\1/p' ./default.nix)"
 if [[ "$new_version" == "$old_version" ]]; then
···
     update-source-version osu-lazer "$new_version"
 fi
 
-$(nix-build . -A osu-lazer.fetch-deps --no-out-link) "$deps_file"
+$(nix-build . -A osu-lazer.fetch-deps --no-out-link)

pkgs/games/space-station-14-launcher/update.sh

···
 set -eo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-deps_file="$(realpath "./deps.nix")"
-
 new_version="$(curl -s "https://api.github.com/repos/space-wizards/SS14.Launcher/releases?per_page=1" | jq -r '.[0].tag_name' | sed 's/v//')"
 old_version="$(sed -nE 's/\s*version = "(.*)".*/\1/p' ./space-station-14-launcher.nix)"
 
···
 
 cd ../../..
 update-source-version space-station-14-launcher.unwrapped "$new_version"
-$(nix-build -A space-station-14-launcher.fetch-deps --no-out-link) "$deps_file"
+$(nix-build -A space-station-14-launcher.fetch-deps --no-out-link)

pkgs/servers/jackett/updater.sh

···
 set -eo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-deps_file="$(realpath "./deps.nix")"
-
 new_version="$(curl -s "https://api.github.com/repos/jackett/jackett/releases?per_page=1" | jq -r '.[0].name')"
 old_version="$(sed -nE 's/\s*version = "(.*)".*/\1/p' ./default.nix)"
 
···
 
 cd ../../..
 update-source-version jackett "${new_version//v}"
-$(nix-build -A jackett.fetch-deps --no-out-link) "$deps_file"
+$(nix-build -A jackett.fetch-deps --no-out-link)

pkgs/servers/jellyfin/update.sh

···
   exit 0
 fi
 
-pushd "$(dirname "${BASH_SOURCE[0]}")"
-nugetDepsFile=$(realpath ./nuget-deps.nix)
-popd
-
 update-source-version jellyfin "$latestVersion"
 
-$(nix-build . -A jellyfin.fetch-deps --no-out-link) "$nugetDepsFile"
+$(nix-build . -A jellyfin.fetch-deps --no-out-link)

pkgs/servers/nosql/eventstore/updater.sh

···
 
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-deps_file="$(realpath "./deps.nix")"
-
 new_version="$(curl -s "https://api.github.com/repos/EventStore/EventStore/releases/latest" | jq -r '.name')"
 new_version="${new_version#oss-v}"
 old_version="$(sed -nE 's/\s*version = "(.*)".*/\1/p' ./default.nix)"
···
 cd ../../../..
 update-source-version eventstore "${new_version//v}"
 
-$(nix-build -A eventstore.fetch-deps --no-out-link) "$deps_file"
+$(nix-build -A eventstore.fetch-deps --no-out-link)

pkgs/tools/X11/opentabletdriver/update.sh

···
 set -eo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-deps_file="$(realpath "./deps.nix")"
-
 new_version="$(curl ${GITHUB_TOKEN:+" -u \":$GITHUB_TOKEN\""} -s "https://api.github.com/repos/OpenTabletDriver/OpenTabletDriver/releases" | jq -r  'map(select(.prerelease == false)) | .[0].tag_name' | cut -c2-)"
 old_version="$(sed -nE 's/\s*version = "(.*)".*/\1/p' ./default.nix)"
 
···
 
 pushd ../../../..
 update-source-version opentabletdriver "$new_version"
-$(nix-build -A opentabletdriver.fetch-deps --no-out-link) "$deps_file"
+$(nix-build -A opentabletdriver.fetch-deps --no-out-link)

pkgs/tools/backup/discordchatexporter-cli/updater.sh

···
 set -eo pipefail
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-deps_file="$(realpath "./deps.nix")"
-
 new_version="$(curl -s "https://api.github.com/repos/tyrrrz/DiscordChatExporter/releases?per_page=1" | jq -r '.[0].name')"
 old_version="$(sed -nE 's/\s*version = "(.*)".*/\1/p' ./default.nix)"
 if [[ "$new_version" == "$old_version" ]]; then
···
 
 cd ../../../..
 update-source-version discordchatexporter-cli "$new_version"
-$(nix-build -A discordchatexporter-cli.fetch-deps --no-out-link) "$deps_file"
+$(nix-build -A discordchatexporter-cli.fetch-deps --no-out-link)

pkgs/tools/misc/depotdownloader/update.sh

···
 
 set -eou pipefail
 
-depsFile="$(realpath "$(dirname "${BASH_SOURCE[0]}")/deps.nix")"
 currentVersion="$(nix eval --raw -f . depotdownloader.version)"
 latestVersion="$(curl -s ${GITHUB_TOKEN:+-u ":$GITHUB_TOKEN"} "https://api.github.com/repos/SteamRE/DepotDownloader/releases?per_page=1" \
     | jq -r '.[].name' | cut -d' ' -f2)"
···
 fi
 
 update-source-version depotdownloader "$latestVersion"
-$(nix-build -A depotdownloader.fetch-deps --no-out-link) "$depsFile"
+$(nix-build -A depotdownloader.fetch-deps --no-out-link)