Add new way for reflective access to static final fields in unit tests of instrumentation projects (#297)

The Field class no longer has a `modifiers` property, so removing the FINAL modifier
doesn't work like it used to with Java 8. Utilize a solution from other libraries
to work around the issue with `com.misc.Unsafe`, encapsulated in a non-Android reflection module

Author: mannodermaus

instrumentation/settings.gradle.kts

@@ -5,3 +5,4 @@ include(":compose")
 include(":runner")
 include(":sample")
 include(":testutil")
+include(":testutil-reflect")

instrumentation/testutil-reflect/build.gradle.kts

@@ -0,0 +1,3 @@
+plugins {
+    kotlin("jvm")
+}

instrumentation/testutil-reflect/src/main/kotlin/de/mannodermaus/junit5/testutil/reflect/Reflections.kt

@@ -0,0 +1,64 @@
+@file:Suppress("removal")
+
+package de.mannodermaus.junit5.testutil.reflect
+
+import sun.misc.Unsafe
+import java.lang.reflect.Field
+import java.lang.reflect.Modifier
+import java.security.AccessController
+import java.security.PrivilegedAction
+
+/**
+ * Adapted from Paparazzi:
+ * https://github.com/cashapp/paparazzi/blob/137f5ca5f3a9949336012298a7c2838fc669c01a/paparazzi/paparazzi/src/main/java/app/cash/paparazzi/Reflections.kt
+ */
+public fun Class<*>.getFieldReflectively(fieldName: String): Field =
+    try {
+        this.getDeclaredField(fieldName).also { it.isAccessible = true }
+    } catch (e: NoSuchFieldException) {
+        throw RuntimeException("Field '$fieldName' was not found in class $name.")
+    }
+
+public fun Field.setStaticValue(value: Any?) {
+    try {
+        this.isAccessible = true
+        val isFinalModifierPresent = this.modifiers and Modifier.FINAL == Modifier.FINAL
+        if (isFinalModifierPresent) {
+            AccessController.doPrivileged<Any?>(
+                PrivilegedAction {
+                    try {
+                        val unsafe =
+                            Unsafe::class.java.getFieldReflectively("theUnsafe").get(null) as Unsafe
+                        val offset = unsafe.staticFieldOffset(this)
+                        val base = unsafe.staticFieldBase(this)
+                        unsafe.setFieldValue(this, base, offset, value)
+                        null
+                    } catch (t: Throwable) {
+                        throw RuntimeException(t)
+                    }
+                }
+            )
+        } else {
+            this.set(null, value)
+        }
+    } catch (ex: SecurityException) {
+        throw RuntimeException(ex)
+    } catch (ex: IllegalAccessException) {
+        throw RuntimeException(ex)
+    } catch (ex: IllegalArgumentException) {
+        throw RuntimeException(ex)
+    }
+}
+
+private fun Unsafe.setFieldValue(field: Field, base: Any, offset: Long, value: Any?) =
+    when (field.type) {
+        Integer.TYPE -> this.putInt(base, offset, (value as Int))
+        java.lang.Short.TYPE -> this.putShort(base, offset, (value as Short))
+        java.lang.Long.TYPE -> this.putLong(base, offset, (value as Long))
+        java.lang.Byte.TYPE -> this.putByte(base, offset, (value as Byte))
+        java.lang.Boolean.TYPE -> this.putBoolean(base, offset, (value as Boolean))
+        java.lang.Float.TYPE -> this.putFloat(base, offset, (value as Float))
+        java.lang.Double.TYPE -> this.putDouble(base, offset, (value as Double))
+        Character.TYPE -> this.putChar(base, offset, (value as Char))
+        else -> this.putObject(base, offset, value)
+    }

instrumentation/testutil/build.gradle.kts

@@ -55,6 +55,8 @@ tasks.withType<Test> {
 }
 
 dependencies {
+  implementation(project(":testutil-reflect"))
+
   api(libs.androidXTestMonitor)
   api(libs.truth)
   api(libs.truthJava8Extensions)

instrumentation/testutil/src/main/kotlin/de/mannodermaus/junit5/testutil/AndroidBuildUtils.kt

@@ -4,29 +4,22 @@ import android.os.Build
 import android.os.Bundle
 import androidx.test.platform.app.InstrumentationRegistry
 import com.google.common.truth.Truth.assertThat
-import java.lang.reflect.Field
-import java.lang.reflect.Modifier
-import kotlin.reflect.KClass
+import de.mannodermaus.junit5.testutil.reflect.getFieldReflectively
+import de.mannodermaus.junit5.testutil.reflect.setStaticValue
 
 object AndroidBuildUtils {
 
-    fun withApiLevel(api: Int, block: () -> Unit) {
-        try {
-            assumeApiLevel(api)
-            block()
-        } finally {
-            resetApiLevel()
-        }
-    }
+    fun withApiLevel(api: Int, block: () -> Unit) = withMockedStaticField<Build.VERSION>(
+        fieldName = "SDK_INT",
+        value = api,
+        block = block,
+    )
 
-    fun withManufacturer(name: String, block: () -> Unit) {
-        try {
-            assumeManufacturer(name)
-            block()
-        } finally {
-            resetManufacturer()
-        }
-    }
+    fun withManufacturer(name: String, block: () -> Unit) = withMockedStaticField<Build>(
+        fieldName = "MANUFACTURER",
+        value = name,
+        block = block,
+    )
 
     fun withMockedInstrumentation(arguments: Bundle = Bundle(), block: () -> Unit) {
         val (oldInstrumentation, oldArguments) = try {
@@ -46,37 +39,20 @@ object AndroidBuildUtils {
         }
     }
 
-    private fun setWithReflection(clazz: KClass<*>, fieldName: String, value: Any?) {
-        // Adjust the value of the target field statically using reflection
-        val field = clazz.java.getDeclaredField(fieldName)
-        field.isAccessible = true
-
-        // Temporarily remove the field's "final" modifier
-        val modifiersField = Field::class.java.getDeclaredField("modifiers")
-        modifiersField.isAccessible = true
-        modifiersField.setInt(field, field.modifiers and Modifier.FINAL.inv())
+    private inline fun <reified T : Any> withMockedStaticField(
+        fieldName: String,
+        value: Any?,
+        block: () -> Unit,
+    ) {
+        val field = T::class.java.getFieldReflectively(fieldName)
+        val oldValue = field.get(null)
 
-        // Apply the value to the field, re-finalize it, then lock it again
-        field.set(null, value)
-        modifiersField.setInt(field, field.modifiers or Modifier.FINAL)
-        field.isAccessible = false
-    }
-
-    private fun assumeApiLevel(apiLevel: Int) {
-        setWithReflection(Build.VERSION::class, "SDK_INT", apiLevel)
-        assertThat(Build.VERSION.SDK_INT).isEqualTo(apiLevel)
-    }
-
-    private fun resetApiLevel() {
-        assumeApiLevel(0)
-    }
-
-    private fun assumeManufacturer(name: String?) {
-        setWithReflection(Build::class, "MANUFACTURER", name)
-        assertThat(Build.MANUFACTURER).isEqualTo(name)
-    }
-
-    private fun resetManufacturer() {
-        assumeManufacturer(null)
+        try {
+            field.setStaticValue(value)
+            assertThat(field.get(null)).isEqualTo(value)
+            block()
+        } finally {
+            field.setStaticValue(oldValue)
+        }
     }
 }