Move isInstalledStatically field to a separate object (Kotlin#2913)

By doing this DebugProbesImpl can check for static installation without having to depend on AgentPremain, which is not compatible with Android.

Co-authored-by: Pierfrancesco Soffritti <psoffritti@google.com>

kotlinx-coroutines-core/jvm/src/debug/AgentPremain.kt

@@ -4,12 +4,12 @@
 
 package kotlinx.coroutines.debug
 
-import kotlinx.coroutines.debug.internal.DebugProbesImpl
+import android.annotation.*
+import kotlinx.coroutines.debug.internal.*
 import sun.misc.*
 import java.lang.instrument.*
 import java.lang.instrument.ClassFileTransformer
 import java.security.*
-import android.annotation.*
 
 /*
  * This class is loaded if and only if kotlinx-coroutines-core was used as -javaagent argument,
@@ -19,15 +19,13 @@ import android.annotation.*
 @SuppressLint("all")
 internal object AgentPremain {
 
-    public var isInstalledStatically = false
-
     private val enableCreationStackTraces = runCatching {
         System.getProperty("kotlinx.coroutines.debug.enable.creation.stack.trace")?.toBoolean()
     }.getOrNull() ?: DebugProbesImpl.enableCreationStackTraces
 
     @JvmStatic
-    public fun premain(args: String?, instrumentation: Instrumentation) {
-        isInstalledStatically = true
+    fun premain(args: String?, instrumentation: Instrumentation) {
+        AgentInstallationType.isInstalledStatically = true
         instrumentation.addTransformer(DebugProbesTransformer)
         DebugProbesImpl.enableCreationStackTraces = enableCreationStackTraces
         DebugProbesImpl.install()
@@ -52,7 +50,7 @@ internal object AgentPremain {
              * on the fly (-> get rid of ASM dependency).
              * You can verify its content either by using javap on it or looking at out integration test module.
              */
-            isInstalledStatically = true
+            AgentInstallationType.isInstalledStatically = true
             return loader.getResourceAsStream("DebugProbesKt.bin").readBytes()
         }
     }

kotlinx-coroutines-core/jvm/src/debug/internal/AgentInstallationType.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.debug.internal
+
+/**
+ * Object used to differentiate between agent installed statically or dynamically.
+ * This is done in a separate object so [DebugProbesImpl] can check for static installation
+ * without having to depend on [kotlinx.coroutines.debug.AgentPremain], which is not compatible with Android.
+ * Otherwise, access to `AgentPremain.isInstalledStatically` triggers the load of its internal `ClassFileTransformer`
+ * that is not available on Android.
+ */
+internal object AgentInstallationType {
+    internal var isInstalledStatically = false
+}

kotlinx-coroutines-core/jvm/src/debug/internal/DebugProbesImpl.kt

@@ -82,7 +82,7 @@ internal object DebugProbesImpl {
     public fun install(): Unit = coroutineStateLock.write {
         if (++installations > 1) return
         startWeakRefCleanerThread()
-        if (AgentPremain.isInstalledStatically) return
+        if (AgentInstallationType.isInstalledStatically) return
         dynamicAttach?.invoke(true) // attach
     }
 
@@ -92,7 +92,7 @@ internal object DebugProbesImpl {
         stopWeakRefCleanerThread()
         capturedCoroutinesMap.clear()
         callerInfoCache.clear()
-        if (AgentPremain.isInstalledStatically) return
+        if (AgentInstallationType.isInstalledStatically) return
         dynamicAttach?.invoke(false) // detach
     }