KTOR-927 Add git hook to check commit message (#2103)

* KTOR-927 Add git hook to check commit message

Author: e5l

CONTRIBUTING.md

@@ -9,13 +9,15 @@ if there is already an open ticket and open a new one if not yet opened.
 
 Contributions are made using Github [pull requests](https://help.github.com/en/articles/about-pull-requests). 
 
-1. [Create](https://github.com/ktorio/ktor/compare) a new PR, your PR should request to merge to the **master** branch.
-2. Ensure that the description is clear, refer to an existing ticket/bug if applicable.
-3. When contributing a new feature, provide motivation and use-cases describing why 
+1. Open (or find) the corresponding [YT](https://youtrack.jetbrains.com/issues/KTOR) issue.
+2. Please make sure that commit messages start with issue number (like `KTOR-1001`). You can copy `githook/prepare-commit-msg` to `.git/hooks` to enable automatic commit message check.
+3. [Create](https://github.com/ktorio/ktor/compare) a new PR, your PR should request to merge to the **master** branch.
+4. Ensure that the description is clear, refer to an existing ticket/bug if applicable.
+5. When contributing a new feature, provide motivation and use-cases describing why 
 the feature is important enough to be delivered with ktor to everyone. 
-4. Adding and updating features may require to update the [documentation](https://github.com/ktorio/ktorio.github.io).
+6. Adding and updating features may require to update the [documentation](https://github.com/ktorio/ktorio.github.io).
 Create a documentation PR and link both pull requests.
-5. Make sure you have adequate tests added and no existing tests were broken. 
+7. Make sure you have adequate tests added and no existing tests were broken. 
 
 # Styleguides
 

githook/prepare-commit-msg

@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+
+import sys
+
+ALLOW = 0
+RESTRICT = 1
+
+
+def is_integer(value: str) -> bool:
+    try:
+        int(value)
+        return True
+    except ValueError as _:
+        return False
+
+
+def is_correct_commit_message(message: str) -> bool:
+    issue_name = first_line.split(" ")[0]
+
+    # Allow fixup commits
+    if issue_name in ["fixup!", "WIP"]:
+        return True
+
+    if issue_name.startswith("~"):
+        return True
+
+    prefix = "KTOR-"
+    if issue_name.startswith(prefix) and is_integer(issue_name[len(prefix):]):
+        return True
+
+    print(f"Commit name should start with the issue number(like KTOR-1001). Current prefix is '{issue_name}'")
+    return False
+
+
+if __name__ == "__main__":
+    commit_message_filename: str = sys.argv[1]
+    with open(commit_message_filename) as file:
+        first_line: str = file.readline()
+
+    exit_code = ALLOW if is_correct_commit_message(first_line) else RESTRICT
+    exit(exit_code)