Ensure the patches are up-to-date and consistent

Add the update-patches.py tool.

Update all the patches, so that the files are up-to-date and use the
same patch file format.

tools/update-patches.py

@@ -0,0 +1,68 @@
+#!/usr/bin/env python
+
+import os
+import os.path
+import subprocess
+
+
+IGNORE = subprocess.DEVNULL
+
+EXERCISES_PATH = "exercises"
+ANSWERS_PATH = "answers"
+PATCHES_PATH = "patches/patches"
+
+
+# Heals all the exercises.
+def heal():
+    maketree(ANSWERS_PATH)
+
+    with os.scandir(EXERCISES_PATH) as it:
+        for entry in it:
+            name = entry.name
+
+            original_path = entry.path
+            patch_path = os.path.join(PATCHES_PATH, patch_name(name))
+            output_path = os.path.join(ANSWERS_PATH, name)
+
+            patch(original_path, patch_path, output_path)
+
+
+def main():
+    heal()
+
+    with os.scandir(EXERCISES_PATH) as it:
+        for entry in it:
+            name = entry.name
+
+            broken_path = entry.path
+            healed_path = os.path.join(ANSWERS_PATH, name)
+            patch_path = os.path.join(PATCHES_PATH, patch_name(name))
+
+            with open(patch_path, "w") as file:
+                term = subprocess.run(
+                    ["diff", broken_path, healed_path],
+                    stdout=file,
+                    text=True,
+                )
+                assert term.returncode == 1
+
+
+def maketree(path):
+    return os.makedirs(path, exist_ok=True)
+
+
+# Returns path with the patch extension.
+def patch_name(path):
+    name, _ = os.path.splitext(path)
+
+    return name + ".patch"
+
+
+# Applies patch to original, and write the file to output.
+def patch(original, patch, output):
+    subprocess.run(
+        ["patch", "-i", patch, "-o", output, original], stdout=IGNORE, check=True
+    )
+
+
+main()