pkgs: add overlay for shell scripts

1 files changed, 76 insertions, 0 deletions

diff --git a/pkgs/shell/default.nix b/pkgs/shell/default.nix
new file mode 100644
index 0000000..119b23e
--- /dev/null
+++ b/pkgs/shell/default.nix
@@ -0,0 +1,76 @@
+self: super:
+
+let
+  inherit (super) lib mylib;
+
+  # Takes a path to a shellscript an builds it into a package.
+  #
+  # The shellscript may contain instructions for modifying the PATH variable:
+  #   #!buildShellBin path=PKGS         resets the PATH variable to the specified packages
+  #   #!buildShellBin append-path=PKGS  append the packages to the PATH variable
+  #   #!buildShellBin prepend-path=PKGS prepend the packages to the PATH variable
+  # where
+  #   PKGS is a non-empty, colon-delimited list of package attribute names, e.g. coreutils:binutils:which
+  buildShellBin = name: path:
+    assert mylib.types.filename.check name; 
+    assert isShellScript path;
+    self.callPackage
+      ({ pkgs }: pkgs.runCommand "${name}" {} /* sh */ ''
+        mkdir -p $out/bin
+        touch $out/bin/${name}
+        chmod +x $out/bin/${name}
+        exec > $out/bin/${name}
+        echo '#! ${pkgs.dash}/bin/dash'
+        echo ${mylib.shell.escape (lib.concatStringsSep "\n" (pathMods pkgs path))}
+        cat ${path}
+      '') {};
+
+  # Determine if a line is an instruction to modify the PATH variable.
+  readPathMod = pkgs: path: line: string: let
+    match = builtins.match "^#! *buildShellBin ((prepend-|append-)?path)=(.*)" string;
+  in
+    lib.optionalAttrs (match != null) {
+      inherit path line;
+      method = builtins.elemAt match 0;
+      packages = map (name: pkgs.${name}) (lib.splitString ":" (builtins.elemAt match 2));
+    };
+
+  # Generate shell assignment to modify the PATH variable.
+  applyPathMod = { method, packages, ... }: {
+    path = /* sh */ "PATH=${lib.makeBinPath packages}";
+    append-path = /* sh */ "PATH=\${PATH+$PATH:}${lib.makeBinPath packages}";
+    prepend-path = /* sh */ "PATH=${lib.makeBinPath packages}\${PATH+:$PATH}";
+  }.${method};
+
+  applyPathMods = mods:
+    assert checkPathMods mods;
+    map applyPathMod mods;
+
+  # Check if a list of list of PATH modifications for sanity.
+  checkPathMods = mods: let
+    index = lib.lists.findFirstIndex (mod: mod.method == "path") 0 mods;
+    mod = lib.elemAt mods index;
+  in
+    if index > 0 then
+      builtins.trace "warning: resetting PATH in ${toString mod.path}:${toString mod.line}" true
+    else
+      true;
+
+  pathMods = pkgs: path:
+    applyPathMods
+      (builtins.filter
+        (x: x != {})
+        (lib.imap1
+          (readPathMod pkgs path)
+          (lib.splitString "\n" (builtins.readFile path))));
+
+  isShellScript = path:
+    mylib.test "#! */bin/sh" (builtins.head (lib.splitString "\n" (builtins.readFile path)));
+
+in
+
+lib.mapAttrs
+  (name: _: buildShellBin name (./. + "/${name}"))
+  (lib.filterAttrs
+    (name: _: name != "default.nix")
+    (builtins.readDir ./.))