Add script to update cargo dependencies

Justfile

@@ -14,3 +14,10 @@ install:
 
 test:
     cargo test --lib --bins
+
+update-dependencies:
+    @cd ./depcheck \
+    && python3 -m venv ./venv \
+    && . ./venv/bin/activate \
+    && pip --disable-pip-version-check install -r ./requirements.txt > /dev/null \
+    && ./update-cargo-dependencies.py

depcheck/.gitignore

@@ -0,0 +1,2 @@
+/crates.io-index/
+/venv/

depcheck/requirements.txt

@@ -0,0 +1,2 @@
+semver==2.13.0
+tomlkit==0.7.2

depcheck/update-cargo-dependencies.py

@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+
+import subprocess
+import os
+import json
+import sys
+
+import semver
+import tomlkit
+
+INDEX_DIR = "crates.io-index"
+
+if os.path.exists(INDEX_DIR):
+    subprocess.run(
+        ["git", "pull", "--depth=1", "origin"],
+        cwd=INDEX_DIR,
+        check=True,
+        capture_output=True,
+    )
+else:
+    subprocess.run(
+        ["git", "clone", "--depth=1", "https://github.com/rust-lang/crates.io-index"],
+        check=True,
+        capture_output=False, # to get some git output
+    )
+
+with open("../Cargo.toml", "r") as cargo_config:
+    cargo = tomlkit.parse(cargo_config.read())
+
+update_necessary = False
+
+for tier in ["dependencies", "dev-dependencies"]:
+    for name, dependency in cargo[tier].items():
+        version = dependency["version"]
+        if len(name) >= 4:
+            info_file = f"{INDEX_DIR}/{name[0:2]}/{name[2:4]}/{name}"
+        elif len(name) == 3:
+            info_file = f"{INDEX_DIR}/3/{name[0]}/{name}"
+        elif len(name) == 2:
+            info_file = f"{INDEX_DIR}/2/{name}"
+        elif len(name) == 1:
+            info_file = f"{INDEX_DIR}/1/{name}"
+
+        current_version = semver.VersionInfo.parse(version)
+
+        latest_version = None
+        for version_entry in open(info_file, "r").readlines():
+            version = semver.VersionInfo.parse(json.loads(version_entry)["vers"])
+            if current_version.prerelease == "" and version.prerelease != "":
+                # skip prereleases, except when we are on a prerelease already
+                continue
+            if latest_version is None or version > latest_version:
+                latest_version = version
+
+        if latest_version != current_version:
+            update_necessary = True
+            if latest_version < current_version:
+                print(
+                    f"{name}: Your current version is newer than the newest version on crates.io, the hell?"
+                )
+            else:
+                print(
+                    f"{name}: New version found: {latest_version} (current {current_version})"
+                )
+                cargo[tier][name]["version"] = str(latest_version)
+
+
+if update_necessary is True:
+    with open("../Cargo.toml", "w") as cargo_config:
+        cargo_config.write(tomlkit.dumps(cargo))
+    sys.exit(1)
+else:
+    print("Everything up to date")
+    sys.exit(0)