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, 38 insertions, 0 deletions

diff --git a/pkgs/profpatsch/execline/run-execline.nix b/pkgs/profpatsch/execline/run-execline.nix
new file mode 100644
index 00000000..40915f25
--- /dev/null
+++ b/pkgs/profpatsch/execline/run-execline.nix
@@ -0,0 +1,38 @@
+{ stdenv, importasCommand, execlinebCommand }:
+{ name
+# the execline script
+, execline
+# additional arguments to pass to the derivation
+, derivationArgs ? {}
+}:
+
+# those arguments can’t be overwritten
+assert !derivationArgs ? system;
+assert !derivationArgs ? name;
+assert !derivationArgs ? builder;
+assert !derivationArgs ? args;
+
+derivation (derivationArgs // {
+  inherit (stdenv) system;
+  inherit name;
+
+  # okay, `builtins.toFile` does not accept strings
+  # that reference drv outputs. This means we need
+  # to pass the script as envvar;
+  # this might clash with another passed envar,
+  # so we give it a long & unique name
+  _runExeclineScript = execline;
+  passAsFile = [ "_runExeclineScript" ]
+            ++ derivationArgs.passAsFile or [];
+
+  builder = importasCommand;
+  args = [
+    "-ui"                    # drop the envvar afterwards
+    "script"                 # substitution name
+    "_runExeclineScriptPath" # passed script file
+    execlinebCommand         # the actual invocation
+    "-P"                     # ignore command line arguments
+    "-W"                     # die on syntax error
+    "$script"                # substituted by importas
+  ];
+})