build(gradle): enable configuration cache, drop configuration-on-demand

apps/flipcash/app/build.gradle.kts

@@ -24,7 +24,7 @@ fun gitVersionCode(): Int {
     return result.toInt().also { println("VersionCode $it") }
 }
 
-val contributorsSigningConfig = ContributorsSignatory(rootProject)
+val contributorsSigningConfig = ContributorsSignatory(rootDir)
 val appNamespace = "${Gradle.flipcashNamespace}.app.android"
 
 android {
@@ -125,8 +125,9 @@ bugsnag {
 }
 
 composeCompiler {
+    // Isolated Projects-safe root access (see AndroidLibraryComposeConventionPlugin).
     stabilityConfigurationFile.set(
-        rootProject.layout.projectDirectory.file("compose_compiler_config.conf")
+        isolated.rootProject.projectDirectory.file("compose_compiler_config.conf")
     )
 }
 

apps/flipcash/benchmark/build.gradle.kts

@@ -2,7 +2,7 @@ plugins {
     id("com.android.test")
 }
 
-val contributorsSigningConfig = ContributorsSignatory(rootProject)
+val contributorsSigningConfig = ContributorsSignatory(rootDir)
 
 android {
     namespace = "com.flipcash.benchmark"

build-logic/convention/src/main/kotlin/AndroidLibraryComposeConventionPlugin.kt

@@ -22,8 +22,12 @@ class AndroidLibraryComposeConventionPlugin : Plugin<Project> {
             }
 
             extensions.configure<ComposeCompilerGradlePluginExtension> {
+                // Use the Isolated Projects-safe accessor for the root directory.
+                // `rootProject.layout` reaches into another project's model, which
+                // Isolated Projects forbids; `isolated.rootProject` is the blessed
+                // read-only view that exposes the root project directory safely.
                 stabilityConfigurationFile.set(
-                    rootProject.layout.projectDirectory.file("compose_compiler_config.conf")
+                    isolated.rootProject.projectDirectory.file("compose_compiler_config.conf")
                 )
             }
 

buildSrc/src/main/java/ContributorsSignatory.kt

@@ -1,19 +1,22 @@
-import org.gradle.api.Project
+import java.io.File
 import java.util.Properties
 
-
-class ContributorsSignatory(project: Project) {
-    private val signingProperties: Properties
-
-    init {
-        val propertiesFile = project.file("contributors.properties")
-        signingProperties = Properties().apply {
-            load(propertiesFile.inputStream())
-        }
+/**
+ * Reads the contributor signing config from `contributors.properties` at the
+ * given [rootDir].
+ *
+ * Takes the root directory as a [File] rather than a [org.gradle.api.Project] so
+ * callers don't reach into another project (`rootProject.file(...)`), which
+ * Isolated Projects forbids. Paths resolve as `Project.file` did: relative
+ * entries against [rootDir], absolute entries as-is.
+ */
+class ContributorsSignatory(rootDir: File) {
+    private val signingProperties: Properties = Properties().apply {
+        rootDir.resolve("contributors.properties").inputStream().use { load(it) }
     }
 
-    val keystore = project.file(signingProperties.getProperty("KEYSTORE_FILE"))
+    val keystore: File = rootDir.resolve(signingProperties.getProperty("KEYSTORE_FILE"))
     val keystorePassword: String = signingProperties.getProperty("KEYSTORE_PASS")
     val keyAlias: String = signingProperties.getProperty("KEY_ALIAS")
     val keyPassword: String = signingProperties.getProperty("KEY_PASS")
-}
+}

gradle.properties

@@ -15,10 +15,12 @@ org.gradle.parallel=true
 # Improves build performance by avoiding redundant task execution
 # More details: https://docs.gradle.org/current/userguide/build_cache.html
 org.gradle.caching=true
-# Enables configuration on demand, making Gradle configure only necessary projects
-# Speeds up builds in multi-project setups by skipping unneeded configurations
-# More details: https://docs.gradle.org/current/userguide/multi_project_builds.html#sec:configuration_on_demand
-org.gradle.configureondemand=true
+# Enables the configuration cache: caches the result of the configuration phase
+# and reuses it across builds, configuring projects in parallel and in isolation.
+# This supersedes configuration-on-demand (which is incompatible with it).
+# Problems fail the build by default, so CI enforces a clean configuration phase.
+# More details: https://docs.gradle.org/current/userguide/configuration_cache.html
+org.gradle.configuration-cache=true
 # AndroidX package structure to make it clearer which packages are bundled with the
 # Android operating system, and which are packaged with your app"s APK
 # https://developer.android.com/topic/libraries/support-library/androidx-rn