ci: generate SDK binary size diff between PRs and main branch

Part of: https://linear.app/customerio/issue/MBL-155/track-the-binary-size-of-our-ios-sdk-upon-every-release

When on a PR, run bloaty to generate a SDK binary size diff report between main branch and PR. This diff report will tell us if the SDK binary size will increases, decreases, or stays the same if the PR gets merged into main.

In order to view the size report, you must view the CI logs. We plan to make the reports more convenient to view by creating PR comments with these reports. I plan to add the PR comments feature in another PR.

commit-id:cb5fe1f3

.github/workflows/build-sample-apps.yml

@@ -124,14 +124,19 @@ jobs:
       env: 
         GOOGLE_CLOUD_MATCH_READONLY_SERVICE_ACCOUNT_B64: ${{ secrets.GOOGLE_CLOUD_MATCH_READONLY_SERVICE_ACCOUNT_B64 }}
         FIREBASE_APP_DISTRIBUTION_SERVICE_ACCOUNT_CREDS_B64: ${{ secrets.FIREBASE_APP_DISTRIBUTION_SERVICE_ACCOUNT_CREDS_B64 }}
-
+    
     # xcodebuild creates builds that include a timestamp in the name. In order for bloaty to read the build, we need to rename it to a static name.
     - name: Rename the same app build to a static name that bloaty can understand  
       working-directory: Apps/${{ matrix.sample-app }}/build/
-      run: mv *.xcarchive App.xcarchive
+      run: mv *.xcarchive App.xcarchive 
+
+    #############
+    # Generate SDK size reports for the SDK size at this commit 
+    #############         
 
-    - name: Print the binary size of our SDK in an app, minus dependencies      
-      # We only need to run bloaty on 1 app.
+    # We only need to run bloaty on 1 app. Therefore, we are hard-coding APN-UIKit into these steps below.
+
+    - name: Print the binary size of our SDK in an app, minus dependencies
       if: ${{ matrix.sample-app == 'APN-UIKit' }}
       working-directory: Apps/${{ matrix.sample-app }}/build/
       run: |
@@ -141,7 +146,6 @@ jobs:
           -n 0
     
     - name: Print the binary size of our SDK in an app, including dependencies
-      # We only need to run bloaty on 1 app.
       if: ${{ matrix.sample-app == 'APN-UIKit' }}
       working-directory: Apps/${{ matrix.sample-app }}/build/
       run: |
@@ -150,9 +154,13 @@ jobs:
           App.xcarchive/Products/Applications/APN\ UIKit.app/APN\ UIKit \
           -n 0
 
+    #############
+    #  Cache main builds for later use
+    #############
+
     # If we are on the main branch, we want to cache the sample app build (.xcarchive directory) for later use.
     # The main branch contains the latest version of our code. So, it's the new baseline that we compare all PRs against. 
-    # By saving the sample app build, we can perform comparisons such as binary size changes between the main branch and the PR branch.
+    # By saving the sample app build, we can perform comparisons such as binary size changes between the main branch and the PR branch.    
 
     - name: Prepare the sample app build to be cached, if this is a main branch build
       if: github.ref == 'refs/heads/main' 
@@ -168,7 +176,7 @@ jobs:
         # https://github.com/actions/cache/blob/main/tips-and-workarounds.md#update-a-cache
         key: ${{ matrix.sample-app }}-build-main-${{ github.run_id }}
         path: Apps/${{ matrix.sample-app }}/build/MainBranchApp.xcarchive
-    
+
     - name: Update sample builds PR comment with build information 
       if: ${{ github.event_name == 'pull_request' }}
       uses: peter-evans/create-or-update-comment@v4
@@ -189,3 +197,37 @@ jobs:
         body: |
           * ${{ matrix.sample-app }}: Build failed. See [CI job logs](https://github.com/${{github.repository}}/actions/runs/${{github.run_id}}) to determine the issue and try re-building. 
         edit-mode: append # append new line to the existing PR comment to build a list of all sample app builds. 
+
+    #############
+    # Generate SDK size diff report between main branch and PR
+    #############    
+
+    # We want to determine if the SDK's binary size will change after merging the PR. 
+    # To do that, we take the latest sample app build from the main branch and the PR branch and compare the SDK sizes between them. 
+    # 
+    # Note: We only need to use 1 sample app build to generate the SDK size diff report. Therefore, we are hard-coding APN-UIKit into these steps below. 
+
+    - name: Download latest main sample app build to generate SDK size diff report 
+      if: github.event_name == 'pull_request' && matrix.sample-app == 'APN-UIKit'
+      uses: actions/cache/restore@v4
+      with:
+        # key param is required for this action to run, but the value has no effect. Therefore, the value is a placeholder value. 
+        # The restore-keys param is what will download the latest cache version for us.
+        key: ThisWillNotMatchAnything-ButValueIsRequiredHere
+        path: Apps/${{ matrix.sample-app }}/build/MainBranchApp.xcarchive
+        # The restore key is what will download the latest cache entry for us. 
+        # 
+        # "If there are multiple partial matches for a restore key, the action returns the most recently created cache."
+        # https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#matching-a-cache-key
+        restore-keys: |
+          ${{ matrix.sample-app }}-build-main-
+
+    - name: Generate SDK binary diff report between main branch and PR
+      if: github.event_name == 'pull_request' && matrix.sample-app == 'APN-UIKit'      
+      working-directory: Apps/${{ matrix.sample-app }}/build/
+      run: |
+        bloaty --source-filter ".*(customerio-ios\/Sources).*" -d compileunits \
+          --debug-file="MainBranchApp.xcarchive/dSYMs/APN UIKit.app.dSYM/Contents/Resources/DWARF/APN UIKit" \
+          --debug-file="App.xcarchive/dSYMs/APN UIKit.app.dSYM/Contents/Resources/DWARF/APN UIKit" \
+          "App.xcarchive/Products/Applications/APN UIKit.app/APN UIKit" -- "MainBranchApp.xcarchive/Products/Applications/APN UIKit.app/APN UIKit"
+