build(shared-core): resolve a local XCFramework when FLIPCASH_SHARED_CORE_LOCAL is set

kmp/shared-core/spm/.gitignore

@@ -0,0 +1,3 @@
+# Left behind by `swift package` / `xcodebuild` runs against this package.
+.build/
+.swiftpm/

kmp/shared-core/spm/Package.swift

@@ -1,5 +1,6 @@
 // swift-tools-version:5.9
 import PackageDescription
+import Foundation
 
 // The publish job rewrites this block — everything else in this file is ours. Note the
 // tags are load-bearing: KMMBridge looks for them verbatim and fails the publish if
@@ -10,6 +11,46 @@ let remoteKotlinChecksum = "b86241d770fa186e44eec4c9ff0ff092d54cf66329828485d243
 let packageName = "SharedCore"
 // END KMMBRIDGE BLOCK
 
+// FLIPCASH_SHARED_CORE_LOCAL points at a code-android-app checkout and swaps the published
+// XCFramework for one assembled from that checkout's Kotlin, so a Kotlin change can be tried
+// from an iOS build without cutting a release and moving a tag:
+//
+//   ./gradlew :kmp:shared-core:assembleSharedCoreReleaseXCFramework
+//
+// This manifest is what gets published, so the override also works from the tagged copy the
+// iOS app resolves — nothing on the iOS side has to change. That copy sits in DerivedData, and
+// SwiftPM only accepts a binary target path relative to the package root, so the absolute path
+// the variable gives us is rewritten as a relative one from wherever the manifest was checked
+// out to.
+//
+// The publish workflow never sets the variable, so CI always resolves the binary target
+// through the URL and checksum above.
+func relativePath(from base: String, to target: String) -> String {
+    let from = (base as NSString).resolvingSymlinksInPath.split(separator: "/").map(String.init)
+    let to = (target as NSString).resolvingSymlinksInPath.split(separator: "/").map(String.init)
+    var shared = 0
+    while shared < from.count, shared < to.count, from[shared] == to[shared] { shared += 1 }
+    return (Array(repeating: "..", count: from.count - shared) + to[shared...]).joined(separator: "/")
+}
+
+let sharedCoreLocalRoot = ProcessInfo.processInfo.environment["FLIPCASH_SHARED_CORE_LOCAL"]
+    .map { ($0 as NSString).expandingTildeInPath }
+    .flatMap { $0.isEmpty ? nil : $0 }
+
+let binaryTarget: Target = sharedCoreLocalRoot.map {
+    .binaryTarget(
+        name: packageName,
+        path: relativePath(
+            from: Context.packageDirectory,
+            to: "\($0)/kmp/shared-core/build/XCFrameworks/release/\(packageName).xcframework"
+        )
+    )
+} ?? .binaryTarget(
+    name: packageName,
+    url: remoteKotlinUrl,
+    checksum: remoteKotlinChecksum
+)
+
 let package = Package(
     name: packageName,
     platforms: [
@@ -25,11 +66,7 @@ let package = Package(
         ),
     ],
     targets: [
-        .binaryTarget(
-            name: packageName,
-            url: remoteKotlinUrl,
-            checksum: remoteKotlinChecksum
-        ),
+        binaryTarget,
         .target(
             name: "SharedCoreKit",
             dependencies: [.target(name: packageName)]