Merge pull request #17837 from MostAwesomeDude/fossil

build-support: Add fetchfossil function.

pkgs/build-support/fetchfossil/builder.sh

@@ -0,0 +1,22 @@
+source $stdenv/setup
+header "Cloning Fossil $url [$rev] into $out"
+
+# Fossil, bless its adorable little heart, wants to write global configuration
+# to $HOME/.fossil. AFAICT, there is no way to disable this functionality.
+# Instead, we'll let it write to the build directory.
+export HOME=$(pwd)
+
+# We must explicitly set the admin user for the clone to something reasonable.
+fossil clone -A nobody "$url" fossil-clone.fossil
+
+mkdir fossil-clone
+WORKDIR=$(pwd)
+mkdir $out
+pushd $out
+fossil open "$WORKDIR/fossil-clone.fossil" "$rev"
+popd
+
+# Just nuke the checkout file.
+rm $out/.fslckout
+
+stopNest

pkgs/build-support/fetchfossil/default.nix

@@ -0,0 +1,20 @@
+{stdenv, fossil}:
+
+{name ? null, url, rev, sha256}:
+
+stdenv.mkDerivation {
+  name = "fossil-archive" + (if name != null then "-${name}" else "");
+  builder = ./builder.sh;
+  buildInputs = [fossil];
+
+  # Envvar docs are hard to find. A link for the future:
+  # https://www.fossil-scm.org/index.html/doc/trunk/www/env-opts.md
+  impureEnvVars = [ "http_proxy" ];
+
+  outputHashAlgo = "sha256";
+  outputHashMode = "recursive";
+  outputHash = sha256;
+
+  inherit url rev;
+  preferLocalBuild = true;
+}

pkgs/top-level/all-packages.nix

@@ -162,6 +162,8 @@ in
 
   fetchdarcs = callPackage ../build-support/fetchdarcs { };
 
+  fetchfossil = callPackage ../build-support/fetchfossil { };
+
   fetchgit = callPackage ../build-support/fetchgit {
     git = gitMinimal;
   };