fix(ios): declare DeveloperSecrets.swift output path & add BUILD_KMP.md

Author: dkhawk

BUILD_KMP.md

@@ -0,0 +1,83 @@
+# Kotlin Multiplatform (KMP) Maps Demo — Build & Run Guide
+
+This guide details how to build and run the multiplatform Maps Compose library (`:maps-compose-multiplatform`), the Android demo app (`:maps-app`), and the iOS demo app (`iosApp`).
+
+---
+
+## 1. Checkout the PR / Branch
+
+Fetch the remote branch and check it out (or add it as a Git worktree):
+
+```bash
+git fetch origin feat/experimental-kmp-module
+git checkout feat/experimental-kmp-module
+```
+
+*(Alternatively, to isolate your work in a worktree branch)*:
+```bash
+git worktree add -b feat/experimental-kmp-module feat-experimental-kmp-module origin/feat/experimental-kmp-module
+```
+
+---
+
+## 2. Configure Local API Keys
+
+Create a file named `secrets.properties` in the **root** directory of the repository (if you don't already have one) and populate it with your Google Maps API keys:
+
+```properties
+MAPS_API_KEY=YOUR_GOOGLE_MAPS_API_KEY
+PLACES_API_KEY=YOUR_GOOGLE_PLACES_API_KEY
+```
+
+> [!IMPORTANT]
+> Both `secrets.properties` and the generated iOS equivalent (`DeveloperSecrets.swift`) are ignored by Git to prevent accidentally leaking credentials.
+
+---
+
+## 3. Building & Running for Android
+
+To compile and verify both the KMP library Android target and the Android sample application (`:maps-app`), run:
+
+```bash
+./gradlew assembleDebug
+```
+
+---
+
+## 4. Building & Running for iOS (Step-by-Step)
+
+If you are running the iOS project (`iosApp`) for the first time, follow these steps on a Mac with **Xcode** and **CocoaPods** installed:
+
+### Step 4.1: Generate the KMP Dummy Framework
+Before CocoaPods can link the local `:maps-compose-multiplatform` podspec, the initial Kotlin framework must exist. From the repository root, execute:
+
+```bash
+./gradlew :maps-compose-multiplatform:generateDummyFramework
+```
+
+### Step 4.2: Generate the Xcode Project
+Navigate to the `iosApp` directory and run the project generation Ruby script (requires the `xcodeproj` gem):
+
+```bash
+cd iosApp
+ruby create_project.rb
+```
+
+> [!NOTE]
+> **Build System Output Tracking (Xcode 16+)**: The `create_project.rb` script declares `$(SRCROOT)/iosApp/DeveloperSecrets.swift` as an output of the **Populate Secrets** script build phase. This prevents modern Xcode build systems from failing with `Build input file cannot be found: DeveloperSecrets.swift` during dependency graph analysis.
+
+### Step 4.3: Install Pod Dependencies
+Install the required CocoaPods (`GoogleMaps` 10.14.0 and the local KMP library). If your local specs repository is out of date, use the `--repo-update` flag:
+
+```bash
+pod install --repo-update
+```
+
+### Step 4.4: Open and Run in Xcode
+1. Open the generated **Workspace** (do **not** open the `.xcodeproj` file directly):
+   ```bash
+   open iosApp.xcworkspace
+   ```
+2. In Xcode's top toolbar, select the active scheme dropdown and set it to **`iosApp`** (instead of `maps_compose_multiplatform`).
+3. Choose an iOS Simulator (e.g., **iPhone 16** or **iPhone 17 Pro**) in the destination dropdown.
+4. Click the **Play** button (or press **Cmd + R**) to compile, run the secrets population script, and launch the app!

iosApp/create_project.rb

@@ -35,6 +35,7 @@
 
 # Add a Build Phase Run Script to populate secrets before compilation
 populate_secrets_phase = target.new_shell_script_build_phase('Populate Secrets')
+populate_secrets_phase.output_paths = ['$(SRCROOT)/iosApp/DeveloperSecrets.swift']
 populate_secrets_phase.shell_script = <<-SHELL
 SECRETS_PATH="${PROJECT_DIR}/../secrets.properties"
 OUTPUT_FILE="${SRCROOT}/iosApp/DeveloperSecrets.swift"