Code reviews with local checkouts and cleaner diffs

When it comes to code reviews, I’ve found that my most helpful feedback starts with checking the code out locally. The limited view on GitHub often falls short; it lacks full context and can’t match the navigability of a local environment. While you can expand the surrounding code on GitHub, it’s tedious and limited to nearby lines. I usually jump to function declarations, usage examples to trace calls, or related parts of the codebase to give meaningful feedback.

To fetch a pull request locally without cluttering my branches, I prefer a headless checkout using the following commands:

#!/bin/bash

# Fetch the latest changes from the remote repository.
git fetch origin

# Fetch the pull request branch by its number.
git fetch origin/pull/${PR_NUMBER}/head

I often discover insights I’d miss in a web view by checking out changes locally.

1. If the update touches an unfamiliar area, I’m more likely to learn about it.
2. Running tests, checking code coverage, or trying alternative solutions becomes effortless.
3. Prototyping suggestions directly in the codebase is now a low-friction task. If I run into issues, I can fix them, provide much better concrete code suggestions, and help the author to polish their pull request.

Hide Whitespace in Diffs

Even with local checkouts, I start by reviewing the diff. When reviewing Go code, for example, hiding whitespace differences is especially important because Go’s auto-formatting can generate many irrelevant diff lines for minor changes. Consider the following struct definitions:

type User struct {
	ID    int
	Name  string
	Email string
}

type Notification struct {
	UserID  string
	Message string
}

type Subscription struct {
	UserID int
	Tier   uint
}

Imagine a pull request adding a CreatedAt field to all three structs. A standard git diff with whitespace changes included would look like this:

diff --git a/model.go b/model.go
index 9c3bd7b..1abe805 100644
--- a/model.go
+++ b/model.go
@@ -1,17 +1,22 @@
 package model
 
+import "time"
+
 type User struct {
-	ID    int
-	Name  string
-	Email string
+	ID        int
+	Name      string
+	Email     string
+	CreatedAt time.Time
 }
 
 type Notification struct {
-	UserID  string
-	Message string
+	UserID    string
+	Message   string
+	CreatedAt time.Time
 }
 
 type Subscription struct {
-	UserID int
-	Tier   uint
+	UserID    int
+	Tier      uint
+	CreatedAt time.Time
 }

Most of these changes are just indentation shifts due to gofmt. This clutters the diff, making it harder to spot the actual code changes. GitHub offers a feature to hide whitespace, but it doesn’t always remember your preferences. Thankfully, git diff can ignore whitespace changes using the --ignore-space-change or -b flag. This allows me to replicate GitHub’s whitespace hiding:

#!/bin/bash

# Show a diff with whitespace ignored between the pull request's common base
# commit and its latest commit (FETCH_HEAD).
git diff -b $(git merge-base origin/main..FETCH_HEAD)..FETCH_HEAD

With -b, the diff now highlights only the relevant changes:

diff --git a/model.go b/model.go
index 9c3bd7b..1abe805 100644
--- a/model.go
+++ b/model.go
@@ -1,17 +1,22 @@
 package model
 
+import "time"
+
 type User struct {
 	ID        int
 	Name      string
 	Email     string
+	CreatedAt time.Time
 }
 
 type Notification struct {
 	UserID    string
 	Message   string
+	CreatedAt time.Time
 }
 
 type Subscription struct {
 	UserID    int
 	Tier      uint
+	CreatedAt time.Time
 }

No distractions and no formatting noise. It’s a minor tweak that makes code reviews faster and more focused.