sterni 318d10e608 chore(nint): move from //users/sterni to //nix

Since //web/bubblegum depends on nint, we need to move it to a non user
directory to conform with the policy established via cl/3434.
Note that this likely doesn't mean greater stability (which isn't
really implied in depot anyways), since I still would like to use a more
elaborate calling convention to allow for additional useful features.

Change-Id: I616f905d8df13e3363674aab69a797b0d39fdd79
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3506
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

2021-09-10 11:08:03 +00:00

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nint — Nix INTerpreter

nint is a shebang compatible interpreter for nix. It is currently implemented as a fairly trivial wrapper around nix-instantiate --eval. It allows to run nix expressions as command line tools if they conform to the following calling convention:

Every nix script needs to evaluate to a function which takes an attribute set as its single argument. Ideally a set pattern with an ellipsis should be used. By default nint passes the following arguments:
- currentDir: the current working directory as a nix path
- argv: a list of arguments to the invokation including the program name at builtins.head argv.
- Extra arguments can be manually passed as described below.
The return value should always be a string (throwing is also okay) which is printed to stdout by nint.

Usage

nint [ --arg ARG VALUE … ] script.nix [ ARGS … ]

Instead of --arg, --argstr can also be used. They both work like the flags of the same name for nix-instantiate and may be specified any number of times as long as they are passed before the nix expression to run.

Below is a shebang which also passes depot as an argument (note the usage of env -S to get around the shebang limitation to two arguments).

#!/usr/bin/env -S nint --arg depot /path/to/depot

Limitations

No side effects except for writing to stdout.
Output is not streaming, i. e. even if the output is incrementally calculated, nothing will be printed until the full output is available. With plain nix strings we can't do better anyways.
Limited error handling for the script, no way to set the exit code etc.

Some of these limitations may be possible to address in the future by using an alternative nix interpreter and a more elaborate calling convention.

Example

Below is a (very simple) implementation of a ls(1)-like program in nix:

#!/usr/bin/env nint
{ currentDir, argv, ... }:

let
  lib = import <nixpkgs/lib>;

  dirs =
    let
      args = builtins.tail argv;
    in
      if args == []
      then [ currentDir ]
      else args;

  makeAbsolute = p:
    if builtins.isPath p
    then p
    else if builtins.match "^/.*" p != null
    then p
    else "${toString currentDir}/${p}";
in

  lib.concatStringsSep "\n"
    (lib.flatten
      (builtins.map
        (d: (builtins.attrNames (builtins.readDir (makeAbsolute d))))
        dirs)) + "\n"

2.4 KiB Raw Blame History

nint — Nix INTerpreter

Usage

Limitations

Example

2.4 KiB

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