ci: add GitHub Actions workflow

.github/workflows/ci.yml

@@ -1,21 +1,45 @@
 name: CI
+
 on:
   push:
-    branches: [main]
+    branches: ["**"]
   pull_request:
     branches: [main]
+
 env:
   CARGO_TERM_COLOR: always
+
 jobs:
   test:
+    name: Test
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
+
+      - name: Install Rust stable
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy, rustfmt
+
+      - name: Cache cargo
+        uses: actions/cache@v4
         with:
-          components: rustfmt, clippy
-      - uses: Swatinem/rust-cache@v2
-      - run: cargo fmt --check
-      - run: cargo clippy -- -D warnings
-      - run: cargo test
-      - run: cargo build --release
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            target/
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+
+      - name: Check formatting
+        run: cargo fmt --all -- --check
+
+      - name: Clippy
+        run: cargo clippy --all-targets --all-features -- -D warnings
+
+      - name: Test
+        run: cargo test --all
+
+      - name: Build release
+        run: cargo build --release

src/cli.rs

@@ -1,7 +1,11 @@
 use clap::{Parser, Subcommand};
 
 #[derive(Parser)]
-#[command(name = "screendiff", about = "Screenshot pixel diff engine — detect visual regressions", version)]
+#[command(
+    name = "screendiff",
+    about = "Screenshot pixel diff engine — detect visual regressions",
+    version
+)]
 pub struct Cli {
     #[command(subcommand)]
     pub command: Commands,

src/main.rs

@@ -1,15 +1,20 @@
 mod cli;
 mod output;
 
-use screendiff::{diff, report};
 use anyhow::Result;
 use clap::Parser;
 use cli::{Cli, Commands};
+use screendiff::{diff, report};
 
 fn main() -> Result<()> {
     let cli = Cli::parse();
     match cli.command {
-        Commands::Compare { before, after, threshold, json } => {
+        Commands::Compare {
+            before,
+            after,
+            threshold,
+            json,
+        } => {
             let result = diff::compare(&before, &after, threshold)?;
             let report = report::build(&before, &after, &result);
             if json {

src/report.rs

@@ -1,5 +1,5 @@
-use serde::{Deserialize, Serialize};
 use crate::diff::DiffResult;
+use serde::{Deserialize, Serialize};
 
 #[derive(Debug, Serialize, Deserialize)]
 pub struct DiffReport {

tests/integration_test.rs

@@ -51,12 +51,8 @@ fn test_compare_help() {
 fn test_identical_images_zero_diff() {
     let a = solid_png(255, 0, 0);
     let b = solid_png(255, 0, 0);
-    let result = diff::compare(
-        a.path().to_str().unwrap(),
-        b.path().to_str().unwrap(),
-        0.01,
-    )
-    .unwrap();
+    let result =
+        diff::compare(a.path().to_str().unwrap(), b.path().to_str().unwrap(), 0.01).unwrap();
     assert_eq!(result.diff_pixels, 0);
     assert_eq!(result.diff_percent, 0.0);
 }
@@ -65,12 +61,8 @@ fn test_identical_images_zero_diff() {
 fn test_completely_different_images_full_diff() {
     let a = solid_png(255, 0, 0);
     let b = solid_png(0, 0, 255);
-    let result = diff::compare(
-        a.path().to_str().unwrap(),
-        b.path().to_str().unwrap(),
-        0.01,
-    )
-    .unwrap();
+    let result =
+        diff::compare(a.path().to_str().unwrap(), b.path().to_str().unwrap(), 0.01).unwrap();
     assert_eq!(result.diff_pixels, 10_000);
     assert_eq!(result.diff_percent, 1.0);
 }
@@ -79,12 +71,8 @@ fn test_completely_different_images_full_diff() {
 fn test_one_pixel_diff_counted() {
     let a = solid_png(255, 0, 0);
     let b = mostly_red_png();
-    let result = diff::compare(
-        a.path().to_str().unwrap(),
-        b.path().to_str().unwrap(),
-        0.01,
-    )
-    .unwrap();
+    let result =
+        diff::compare(a.path().to_str().unwrap(), b.path().to_str().unwrap(), 0.01).unwrap();
     assert_eq!(result.diff_pixels, 1);
 }
 
@@ -110,12 +98,8 @@ fn test_dimension_mismatch_returns_error() {
 fn test_zero_diff_verdict_is_pass() {
     let a = solid_png(0, 255, 0);
     let b = solid_png(0, 255, 0);
-    let result = diff::compare(
-        a.path().to_str().unwrap(),
-        b.path().to_str().unwrap(),
-        0.01,
-    )
-    .unwrap();
+    let result =
+        diff::compare(a.path().to_str().unwrap(), b.path().to_str().unwrap(), 0.01).unwrap();
     let rep = report::build("a.png", "b.png", &result);
     assert!(matches!(rep.verdict, Verdict::Pass));
 }
@@ -124,12 +108,8 @@ fn test_zero_diff_verdict_is_pass() {
 fn test_over_threshold_verdict_is_fail() {
     let a = solid_png(255, 0, 0);
     let b = solid_png(0, 0, 255);
-    let result = diff::compare(
-        a.path().to_str().unwrap(),
-        b.path().to_str().unwrap(),
-        0.01,
-    )
-    .unwrap();
+    let result =
+        diff::compare(a.path().to_str().unwrap(), b.path().to_str().unwrap(), 0.01).unwrap();
     let rep = report::build("a.png", "b.png", &result);
     assert!(matches!(rep.verdict, Verdict::Fail));
 }
@@ -139,12 +119,8 @@ fn test_single_pixel_diff_within_threshold_passes() {
     // 1 changed pixel in 10000 = 0.0001 — well under 1% threshold
     let a = solid_png(255, 0, 0);
     let b = mostly_red_png();
-    let result = diff::compare(
-        a.path().to_str().unwrap(),
-        b.path().to_str().unwrap(),
-        0.01,
-    )
-    .unwrap();
+    let result =
+        diff::compare(a.path().to_str().unwrap(), b.path().to_str().unwrap(), 0.01).unwrap();
     let rep = report::build("a.png", "b.png", &result);
     assert!(matches!(rep.verdict, Verdict::Pass));
 }