feat: new rule for nix-shell

README.md

@@ -367,6 +367,7 @@ The following rules are enabled by default on specific platforms only:
 * `brew_update_formula` &ndash; turns `brew update <formula>` into `brew upgrade <formula>`;
 * `dnf_no_such_command` &ndash; fixes mistyped DNF commands;
 * `nixos_cmd_not_found` &ndash; installs apps on NixOS;
+* `nix_shell` &ndash; re-runs your command in a `nix-shell`;
 * `pacman` &ndash; installs app with `pacman` if it is not installed (uses `yay`, `pikaur` or `yaourt` if available);
 * `pacman_invalid_option` &ndash; replaces lowercase `pacman` options with uppercase.
 * `pacman_not_found` &ndash; fixes package name with `pacman`, `yay`, `pikaur` or `yaourt`.

tests/rules/test_nix_shell.py

@@ -0,0 +1,90 @@
+import pytest
+from thefuck.rules.nix_shell import get_nixpkgs_names, match, get_new_command
+from thefuck.types import Command
+from unittest.mock import patch, MagicMock
+
+
+@pytest.mark.parametrize(
+    "script,output,nixpkgs_names",
+    [
+        # output can be retrived by running `THEFUCK_DEBUG=true thefuck lsof`
+        (
+            "lsof",
+            "/nix/store/p6dlr3skfhxpyphipg2bqnj52999banh-bash-5.2-p15/bin/sh: line 1: lsof: command not found",
+            ["lsof"],
+        ),
+    ],
+)
+def test_match(script, output, nixpkgs_names):
+    with patch("thefuck.rules.nix_shell.get_nixpkgs_names") as mocked_get_nixpkgs_names:
+        mocked_get_nixpkgs_names.return_value = nixpkgs_names
+        command = Command(script, output)
+        assert match(command)
+
+
+@pytest.mark.parametrize(
+    "script,output,nixpkgs_names",
+    [
+        # output can be retrived by running `THEFUCK_DEBUG=true thefuck foo`
+        (
+            "foo",
+            "/nix/store/p6dlr3skfhxpyphipg2bqnj52999banh-bash-5.2-p15/bin/sh: line 1: foo: command not found",
+            [],
+        ),
+    ],
+)
+def test_not_match(script, output, nixpkgs_names):
+    with patch("thefuck.rules.nix_shell.get_nixpkgs_names") as mocked_get_nixpkgs_names:
+        mocked_get_nixpkgs_names.return_value = nixpkgs_names
+        command = Command(script, output)
+        assert not match(command)
+
+
+@pytest.mark.parametrize(
+    "script,nixpkgs_names,new_command",
+    [
+        (
+            "lsof -i :3000",
+            ["busybox", "lsof"],
+            [
+                'nix-shell -p busybox --run "lsof -i :3000"',
+                'nix-shell -p lsof --run "lsof -i :3000"',
+            ],
+        ),
+        ("xev", ["xorg.xev"], ['nix-shell -p xorg.xev --run "xev"']),
+    ],
+)
+def test_get_new_command(script, nixpkgs_names, new_command):
+    """Check that flags and params are preserved in the new command"""
+
+    command = Command(script, "")
+    with patch("thefuck.rules.nix_shell.get_nixpkgs_names") as mocked_get_nixpkgs_names:
+        mocked_get_nixpkgs_names.return_value = nixpkgs_names
+        assert get_new_command(command) == new_command
+
+
+# Mocks the stderr of `command-not-found QUERY`. Mock values are retrieved by
+# running `THEFUCK_DEBUG=true thefuck command-not-found lsof`.
+mocked_cnf_stderr = {
+    "lsof": "The program 'lsof' is not in your PATH. It is provided by several packages.\nYou can make it available in an ephemeral shell by typing one of the following:\n  nix-shell -p busybox\n  nix-shell -p lsof",
+    "xev": "The program 'xev' is not in your PATH. You can make it available in an ephemeral shell by typing:\n  nix-shell -p xorg.xev",
+    "foo": "foo: command not found",
+}
+
+
+@pytest.mark.parametrize(
+    "bin,expected_nixpkgs_names,cnf_stderr",
+    [
+        ("lsof", ["busybox", "lsof"], mocked_cnf_stderr["lsof"]),
+        ("xev", ["xorg.xev"], mocked_cnf_stderr["xev"]),
+        ("foo", [], mocked_cnf_stderr["foo"]),
+    ],
+)
+def test_get_nixpkgs_names(bin, expected_nixpkgs_names, cnf_stderr):
+    """Check that `get_nixpkgs_names` returns the correct names"""
+
+    with patch("subprocess.run") as mocked_run:
+        result = MagicMock()
+        result.stderr = cnf_stderr
+        mocked_run.return_value = result
+        assert get_nixpkgs_names(bin) == expected_nixpkgs_names

thefuck/rules/nix_shell.py

@@ -0,0 +1,51 @@
+from thefuck.specific.nix import nix_available
+import subprocess
+
+enabled_by_default = nix_available
+
+# Set the priority just ahead of `fix_file` rule, which can generate low quality matches due
+# to the sheer amount of paths in the nix store.
+priority = 999
+
+
+def get_nixpkgs_names(bin):
+    """
+    Returns the name of the Nix package that provides the given binary. It uses the
+    `command-not-found` binary to do so, which is how nix-shell generates it's own suggestions.
+    """
+
+    result = subprocess.run(
+        ["command-not-found", bin], stderr=subprocess.PIPE, universal_newlines=True
+    )
+
+    # The suggestion, if any, will be found in stderr. Upstream definition: https://github.com/NixOS/nixpkgs/blob/b6fbd87328f8eabd82d65cc8f75dfb74341b0ace/nixos/modules/programs/command-not-found/command-not-found.nix#L48-L90
+    text = result.stderr
+
+    # return early if binary is not available through nix
+    if "nix-shell" not in text:
+        return []
+
+    nixpkgs_names = [
+        line.split()[-1] for line in text.splitlines() if "nix-shell -p" in line
+    ]
+    return nixpkgs_names
+
+
+def match(command):
+    bin = command.script_parts[0]
+    return (
+        "command not found" in command.output  # only match commands which had exit code: 127                   # noqa: E501
+        and get_nixpkgs_names(bin)             # only match commands which could be made available through nix  # noqa: E501
+    )
+
+
+def get_new_command(command):
+    bin = command.script_parts[0]
+    nixpkgs_names = get_nixpkgs_names(bin)
+
+    # Construct a command for each package name
+    commands = [
+        'nix-shell -p {} --run "{}"'.format(name, command.script)
+        for name in nixpkgs_names
+    ]
+    return commands