README.md

README.md

@@ -1,5 +1,82 @@
 # gh-stack
 
+I use this tool to help managed stacked pull requests on Github, which are notoriously difficult to manage manually. Here are a few examples of the kind of things I'm talking about:
+
+- https://unhashable.com/stacked-pull-requests-keeping-github-diffs-small
+- https://stackoverflow.com/questions/26619478/are-dependent-pull-requests-in-github-possible
+- https://gist.github.com/Jlevyd15/66743bab4982838932dda4f13f2bd02a
+
+This tool assumes that all PRs in a single "stack" all have a unique identifier in their title (I typically use a Jira ticket number for this). It then looks for all PRs containing this containing this identifier and builds a dependency graph in memory. This can technically support a "branched stack" instead of a single chain, but I haven't really tried the latter style (which seems much more complex).
+
+With this graph built up, the tool can:
+
+- Add a markdown table to the PR description (idempotently) of each PR in the stack describing _all_ PRs in the stack.
+- Log a simple list of all PRs in the stack (+ dependencies) to stdout.
+- Emit a bash script that can update all PRs in the stack.
+  - This generally happens in the event of:
+    - The PR at the base of the stack is merged, leaving all the remaining PRs in a conflicted state.
+    - One of the PRs (not the top of the stack) has a commit added to it, leaving all dependent PRs in a conflicted state.
+  - The script requires two placeholders to be manually specified before execution.
+
+## Usage
+
+```bash
+$ export GHSTACK_OAUTH_TOKEN='<personal access token>'
+
+# Idempotently add a markdown table summarizing the stack
+# to the description of each PR in the stack.
+$ gh-stack github 'stack-identifier'
+
+# Same as above, but precede the markdown table with the 
+# contents of `filename.txt`.
+$ gh-stack github 'stack-identifier' filename.txt
+
+# Print a description of the stack to stdout.
+$ gh-stack log 'stack-identifier'
+
+# Emit a bash script that can update a stack in the case of conflicts.
+# WARNING: This script could potentially cause destructive behavior.
+$ gh-stack rebase 'stack-identifier'
 ```
-gh-stack <pattern>
-```
+  
+## Strategy
+
+Here's a quick summary of the strategy that the bash script described above uses to keep the stack up-to-date.
+
+Let's use this stack as an example:
+
+![](img/initial.png)
+
+## Feature Changes
+
+In the first case, let's assume that "feature part 1" had some changes added to it in the form of a commit; this leaves parts 2 & 3 in a conflicted state:
+
+![](img/feature-1.png)
+
+The script requires that you pass in a `PREBASE` (which is essentially the boundary for the feature part you're operating on, the last/oldest commit in feature-part-2 in this case). 
+An initial `TO` ref is also required, which is the point upon which you want to rebase the rest of the stack. In this case, that ref is `remote/feature-part-1`).
+
+The script executes a single step, we now have this intermediate state:
+
+![](img/feature-2.png)
+
+The script completes execution, and we now have this final state with the entire stack updated/recreated:
+
+![](img/feature-3.png)
+
+## Feature Complete & Merged
+
+In the second case, let's assume that "feature part 2" is done and has been merged to `develop`:
+
+![](/img/complete-1.png)
+
+This immediately leaves feature parts 2 & 3 in a conflicted state. The script can fix this situation as well.
+As before, pass a `PREBASE` (in this case the oldest commit in feature part 2) and an initial `TO` ref to rebase on (in this case `remote/develop`).
+
+Once the script executes a single step, we're left with:
+
+![](/img/complete-2.png)
+
+And once the script is done:
+
+![](img/complete-3.png)