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README.md

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+# nixpkgs-updater
+
+Update packages in nixpkgs likes it is 2020.
+This tool is still in early development.
+
+## Dependencies
+
+- python 3
+- [nix-prefetch](https://github.com/msteen/nix-prefetch/)
+
+## USAGE
+
+````
+$ NIX_PATH=nixpkgs=/path/to/git python nixpkgs-updater.py attribute [version]
+```
+
+Example:
+
+````
+$ NIX_PATH=nixpkgs=/path/to/git python nixpkgs-updater.py nixpkgs-review
+```
+
+(fetches the latest github release)
+
+or:
+
+```
+$ NIX_PATH=nixpkgs=/path/to/git python nixpkgs-updater.py nixpkgs-review 2.1.1
+```

nixpkgs-update.py

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+#!/usr/bin/env python3
+
+import fileinput
+import json
+import subprocess
+import sys
+import urllib.request
+import xml.etree.ElementTree as ET
+from typing import Optional
+from urllib.parse import urlparse
+
+
+def eval_attr(attr: str) -> str:
+    return f"""(with import <nixpkgs> {{}};
+    let
+      pkg = {attr};
+    in {{
+      position = pkg.meta.position;
+      url = pkg.src.meta.homepage;
+      hash = pkg.src.outputHash;
+      version = (builtins.parseDrvName pkg.name).version;
+    }})"""
+
+
+def fetch_latest_release(url_str: str) -> str:
+    url = urlparse(url_str)
+    parts = url.path.split("/")
+    owner, repo = parts[1], parts[2]
+    assert url.netloc == "github.com"
+    resp = urllib.request.urlopen(f"https://github.com/{owner}/{repo}/releases.atom")
+    tree = ET.fromstring(resp.read())
+    release = tree.find(".//{http://www.w3.org/2005/Atom}entry")
+    assert release is not None
+    link = release.find("{http://www.w3.org/2005/Atom}link")
+    assert link is not None
+    href = link.attrib["href"]
+    url = urlparse(href)
+    return url.path.split("/")[-1]
+
+
+def sed(filename: str, search: str, replace: str):
+    with fileinput.FileInput(filename, inplace=True) as f:
+        for line in f:
+            print(line.replace(search, replace), end="")
+
+
+def update(attr: str, latest_version: Optional[str]) -> None:
+    res = subprocess.run(
+        ["nix", "eval", "--json", eval_attr(attr)], text=True, stdout=subprocess.PIPE,
+    )
+    out = json.loads(res.stdout)
+    current_version: str = out["version"]
+    current_hash: str = out["hash"]
+    filename, line = out["position"].rsplit(":", 1)
+
+    if not latest_version:
+        latest_version = fetch_latest_release(out["url"])
+
+    if current_version != latest_version:
+        sed(filename, current_version, latest_version)
+    res2 = subprocess.run(
+        ["nix-prefetch", "-A", attr], text=True, stdout=subprocess.PIPE
+    )
+    latest_hash = res2.stdout.strip()
+    if current_hash != latest_hash:
+        sed(filename, current_hash, latest_hash)
+
+
+def main() -> None:
+    if len(sys.argv) < 2:
+        print(f"USAGE: {sys.argv[0]} package-name [version]")
+        sys.exit(1)
+    package_attr = sys.argv[1]
+    package_attr = sys.argv[1]
+    if len(sys.argv) == 3:
+        version = sys.argv[2]
+    update(package_attr, version)
+
+
+if __name__ == "__main__":
+    main()