Rules for commit messages

Part of KTI-944 about adding automatic checks to commit messages.

.idea/vcs.xml

@@ -4,7 +4,7 @@
     <profile version="1.0">
       <inspection_tool class="BodyLimit" enabled="true" level="WARNING" enabled_by_default="true" />
       <inspection_tool class="GrazieCommit" enabled="true" level="TYPO" enabled_by_default="true" />
-      <inspection_tool class="SubjectBodySeparation" enabled="true" level="WARNING" enabled_by_default="true" />
+      <inspection_tool class="SubjectBodySeparation" enabled="true" level="ERROR" enabled_by_default="true" />
       <inspection_tool class="SubjectLimit" enabled="true" level="WARNING" enabled_by_default="true" />
     </profile>
   </component>

docs/contributing.md

@@ -60,6 +60,35 @@ git config --global pull.rebase true
 This will avoid your local repo having too many merge commits
 which will help keep your pull request simple and easy to apply.
 
+## Rules for commit messages
+
+Most of these rules are originated from the [How to Write a Git Commit Message](https://chris.beams.io/posts/git-commit/) 
+article, and it's highly recommended to read it.
+
+### Rules on commit messages' content
+
+1. Use the body to explain what and why vs. how
+   * Please make an extra effort to explain why changes are needed for every non-trivial modification.
+2. Significant commits must mention relevant [YouTrack](https://youtrack.jetbrains.com/issues/KT) issues in their messages
+3. Commit changes together with the corresponding tests, unless the resulting commit becomes too unwieldy to grasp
+4. Try to avoid commits like *"Fixes after review"* whenever it's possible and squash them with meaningful ones instead
+5. Keep the subject (first line of the commit message) clean and readable. All additional information and directives for external tools 
+should be moved to the message body.
+6. If you mention “*^[KTIJ-235](https://youtrack.jetbrains.com/issue/KTIJ-235) Fixed*” in the message body - then the VCS integration will 
+add *Fix in Builds* field to the issue in the YouTrack and automatically mark issue as fixed. For details see 
+[YouTrack Integrations](https://www.jetbrains.com/youtrack/features/integrations.html) and 
+[Apply Commands in VCS Commits](https://www.jetbrains.com/help/youtrack/server/Apply-Commands-in-VCS-Commits.html).
+
+### Rules on commit messages' style/formatting
+
+1. Separate subject from body with a blank line
+2. Capitalize the subject line
+3. Do not end the subject line with a period
+4. Use the imperative mood in the subject line
+5. Limit the commit messages lines to 72 characters
+   * Use “Commit Message Inspections” in IntelliJ IDE *Settings -> Version Control -> Commit*
+   * vim: ```autocmd FileType gitcommit setlocal textwidth=72```
+
 ## Checklist
 
 Before submitting the pull request, make sure that you can say "YES" to each point in this short checklist: