pkgs/profpatsch: WIP execline experiments

* runExecline: like runCommand, but a lot more lightweight
* symlink: symlink a given list of links together
* importer: a small DSL to “import” “modules” into a build context

Some highlights:
* runExecline does not use any stdenv (apart from the `execline` build)
* symlink uses netstrings to pass correct fields into the derivation
* no use of bash, everything uses execline.

1 files changed, 50 insertions, 0 deletions

diff --git a/pkgs/profpatsch/execline/symlink.nix b/pkgs/profpatsch/execline/symlink.nix
new file mode 100644
index 00000000..ca8684d2
--- /dev/null
+++ b/pkgs/profpatsch/execline/symlink.nix
@@ -0,0 +1,50 @@
+{ lib, s6-portable-utils, coreutils, runExecline }:
+# DrvPath :: path relative to the derivation
+# AbsPath :: absolute path in the store
+#    Name
+# -> List (Symlink { dest: DrvPath, orig: AbsPath })
+# -> Drv
+name: links:
+
+let
+  toNetstring = s:
+    "${toString (builtins.stringLength s)}:${s},";
+
+in
+runExecline {
+  inherit name;
+
+  derivationArgs = {
+    pathTuples = lib.concatMapStrings
+      ({dest, orig}: toNetstring
+        (toNetstring dest + (toNetstring orig)))
+      links;
+    passAsFile = [ "pathTuples" ];
+    # bah! coreutils just for cat :(
+    PATH = lib.makeBinPath [ s6-portable-utils ];
+  };
+
+  execline = ''
+    importas -ui p pathTuplesPath
+    importas -ui out out
+    forbacktickx -d "" destorig { ${coreutils}/bin/cat $p }
+      importas -ui do destorig
+      multidefine -d "" $do { destsuffix orig }
+      define dest ''${out}/''${destsuffix}
+
+      # this call happens for every file, not very efficient
+      foreground {
+        backtick -n d { s6-dirname $dest }
+        importas -ui d d
+        s6-mkdir -p $d
+      }
+
+      ifthenelse { s6-test -L $orig } {
+        backtick -n res { s6-linkname -f $orig }
+        importas -ui res res
+        s6-ln -fs $res $dest
+      } {
+        s6-ln -fs $orig $dest
+      }
+  '';
+}