Add patches to your stack

We're going to focus on how we create patches on our stack and what a stack is in terms of git?

TL;DR

A stack is simply a branch with an upstream tracking branch, e.g. main with an upstream tracking branch of origin/main. You can create a patch on top of your stack with the following.

Make a change locally in your editor of choice
Stage your change with git add -p
Create patch (a.k.a. commit) with git commit

WalkThrough

Git Patch Stack is really just a layer of tooling built directly on top of git. So if we look at our git tree here, we have a small project.

Initial git tree with skeleton

It has an initial skeleton of a Rust project. That's just a Hello World program right now, and we can see we have a branch called main that were checked out on. That's why HEAD points to it, and we then have an upstream main with a remote of origin. It happens to be where main points to on our GitHub repository for this.

Technically, in Git Patch Stack terms, any branch that has an upstream tracking branch is a Patch Stack. So you can have as many of these Patch Stacks as you want, as long as they are branches that have an upstream tracking branch. To add patches on to a stack, you first have to be checked out on a branch that has an associated upstream tracking branch. In our case, main.

Make a change

Then we just make changes like we normally would in git. We add a commit and that commit conceptually becomes a patch. So let's do that real quick. Let's go look at our source code here. We have a main() function.

fn main() {
    println!("Hello, world!");
}

Let's say that we want to add another function called foo() for some reason, and we want this function to print "Foo", nothing too crazy. So we add a function. We're not even going to use the function. We're just going to add it to the code base so that we can use it in the future.

fn main() {
    println!("Hello, world!");
}

fn foo() {
    println!("Foo");
}

That's it. Now we just do a git diff to verify our changes.

diff --git a/src/main.rs b/src/main.rs
index e7a11a9..0e47771 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,7 @@
 fn main() {
     println!("Hello, world!");
 }
+
+fn foo() {
+    println!("Foo");
+}

I have a git alias of di setup, so I can just run git di to get the diff quicker.

Once we verify the change is what we want, then we stage that change. We can stage that change by doing a git add. Now we can do a git diff --cached and that will show us all the changes that are staged as a diff.

diff --git a/src/main.rs b/src/main.rs
index e7a11a9..0e47771 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,7 @@
 fn main() {
     println!("Hello, world!");
 }
+
+fn foo() {
+    println!("Foo");
+}

It looks good. Looks like the changes we want.

I have a git alias of dc setup, so I can just run git dc to get the staged diff quicker.

Create Patch on Stack

If we do a git commit, it pops up the configured editor, and we can enter the commit message.

Add foo() function

So that in the future we can print the message when necessary.

Ideally, we would provide more context but because this is a contrived example. We don't really have it. Now we have a commit (a.k.a. patch).

Added foo() commit

If we look at our git tree, you can see we have a commit here that we're pointing to on main, which is the "Add foo() function" patch. And then underneath that in the tree, we have the initial skeleton commit we had before.

Now, if we run gps ls, which is how we list our stack of patches.

We can now see that our stack of patches consists of one patch.

Add another Patch

So let's add another one real quick just so we can see what it's like to have two. Let's just copy this and paste that, and change this word to bar, change this to bar, and then we'll add another function.

fn main() {
    println!("Hello, world!");
}

fn foo() {
    println!("Foo");
}

fn bar() {
    println!("Bar");
}

Now we just git add, git dc to verify our staged code. All looks good. We create another patch using git commit and enter the message.

Add bar() function

So that we can print the "Bar" message in the future.

Now we should have two patches in our stack.

We have patches zero, which is the index of the "Add foo() function" patch. And we have patch one which is the index of the "Add bar() function" patch.

The short SHA of these patches, a.k.a. commits, is visible to the right of the index and status space. We can also see the patch summaries to the right of the short SHA.

As you get into Git Patch Stack further, you'll see status indications here that will indicate things like whether that patch has been requested for review, the patch has been integrated, or if there's been changes since you requested review. But for now that's it.

That's how you add a patch to the top of your stack.

Hope you enjoyed.

Git Patch Stack Book