r8 不创建输出 dex 文件

Question

我正在尝试使用 r8 但没有成功：

$ wget https://repo1.maven.org/maven2/com/mikepenz/fastadapter/3.2.7/fastadapter-3.2.7.aar
$ wget https://maven.google.com/com/android/support/recyclerview-v7/26.0.1/recyclerview-v7-26.0.1.aar
$ unzip fastadapter-3.2.7.aar      && mv classes.jar fastadapter.jar
$ unzip recyclerview-v7-26.0.1.aar && mv classes.jar recycleview.jar
$ echo "-dontwarn java.lang.Object" > proguard.cfg
$ java -jar build/libs/r8.jar --lib android-4.1.1.4.jar --lib recycleview.jar --release --output . --pg-conf proguard.cfg fastadapter.jar
$ dexdump -d classes.dex | grep "insns size" | wc -l
Unable to open 'classes.dex' : No such file or directory
0

但使用 d8 时效果完美（即使没有 --lib android.jar 和 --lib recycleview.jar）：

$ java -jar ../build/libs/d8.jar --release --output . fastadapter.jar
$ dexdump -d classes.dex | grep "insns size" | wc -l
390

编辑

尝试创建 fastadapter proguard keep 规则失败：

$ cmdline-tools/build-tools/30.0.3/aapt2 link --proguard proguard_fastadapter.cfg -o proguard_fastadapter.cfg --manifest AndroidManifest.xml
AndroidManifest.xml:2: error: attribute android:versionCode not found.
AndroidManifest.xml:2: error: attribute android:versionName not found.
AndroidManifest.xml:7: error: attribute android:minSdkVersion not found.
AndroidManifest.xml:7: error: attribute android:targetSdkVersion not found.
error: failed processing manifest.

这有点奇怪，因为 targetSdkVersion 实际上确实存在：

$ grep "targetSdkVersion" AndroidManifest.xml
        android:targetSdkVersion="27" />

Answer 1

问题是您传递给 R8 的唯一规则是 -dontwarn java.lang.Object。没有单一的 -keep 规则，这意味着输出将为空，因为没有保留入口点。

缺少的是两套保留规则：

1. 所有 Android 应用程序的一般保留规则
2. 具有所有入口点的具体应用程序的特定规则（来自平台的反射访问，例如视图 inflation），可以使用 aapt2.
生成

对于第一组规则 Android Studio（或更准确地说是 AGP）捆绑了此规则文件，该文件作为 getDefaultProguardFile('proguard-android-optimize.txt').

的结果传递给所有构建

# This is a configuration file for ProGuard.
# http://proguard.sourceforge.net/index.html#manual/usage.html
#
# Starting with version 2.2 of the Android plugin for Gradle, this file is distributed together with
# the plugin and unpacked at build-time. The files in $ANDROID_HOME are no longer maintained and
# will be ignored by new version of the Android plugin for Gradle.

# Optimizations: If you don't want to optimize, use the proguard-android.txt configuration file
# instead of this one, which turns off the optimization flags.
# Adding optimization introduces certain risks, since for example not all optimizations performed by
# ProGuard works on all versions of Dalvik.  The following flags turn off various optimizations
# known to have issues, but the list may not be complete or up to date. (The "arithmetic"
# optimization can be used if you are only targeting Android 2.0 or later.)  Make sure you test
# thoroughly if you go this route.
-optimizations !code/simplification/arithmetic,!code/simplification/cast,!field/*,!class/merging/*
-optimizationpasses 5
-allowaccessmodification

-dontusemixedcaseclassnames
-dontskipnonpubliclibraryclasses
-verbose

# Preserve some attributes that may be required for reflection.
-keepattributes *Annotation*,Signature,InnerClasses,EnclosingMethod

-keep public class com.google.vending.licensing.ILicensingService
-keep public class com.android.vending.licensing.ILicensingService
-keep public class com.google.android.vending.licensing.ILicensingService
-dontnote com.android.vending.licensing.ILicensingService
-dontnote com.google.vending.licensing.ILicensingService
-dontnote com.google.android.vending.licensing.ILicensingService

# For native methods, see http://proguard.sourceforge.net/manual/examples.html#native
-keepclasseswithmembernames,includedescriptorclasses class * {
    native <methods>;
}

# Keep setters in Views so that animations can still work.
-keepclassmembers public class * extends android.view.View {
    void set*(***);
    *** get*();
}

# We want to keep methods in Activity that could be used in the XML attribute onClick.
-keepclassmembers class * extends android.app.Activity {
    public void *(android.view.View);
}

# For enumeration classes, see http://proguard.sourceforge.net/manual/examples.html#enumerations
-keepclassmembers enum * {
    public static **[] values();
    public static ** valueOf(java.lang.String);
}

-keepclassmembers class * implements android.os.Parcelable {
    public static final ** CREATOR;
}

# Preserve annotated Javascript interface methods.
-keepclassmembers class * {
    @android.webkit.JavascriptInterface <methods>;
}

# The support libraries contains references to newer platform versions.
# Don't warn about those in case this app is linking against an older
# platform version. We know about them, and they are safe.
-dontnote android.support.**
-dontnote androidx.**
-dontwarn android.support.**
-dontwarn androidx.**

# This class is deprecated, but remains for backward compatibility.
-dontwarn android.util.FloatMath

# Understand the @Keep support annotation.
-keep class android.support.annotation.Keep
-keep class androidx.annotation.Keep

-keep @android.support.annotation.Keep class * {*;}
-keep @androidx.annotation.Keep class * {*;}

-keepclasseswithmembers class * {
    @android.support.annotation.Keep <methods>;
}

-keepclasseswithmembers class * {
    @androidx.annotation.Keep <methods>;
}

-keepclasseswithmembers class * {
    @android.support.annotation.Keep <fields>;
}

-keepclasseswithmembers class * {
    @androidx.annotation.Keep <fields>;
}

-keepclasseswithmembers class * {
    @android.support.annotation.Keep <init>(...);
}

-keepclasseswithmembers class * {
    @androidx.annotation.Keep <init>(...);
}

# These classes are duplicated between android.jar and org.apache.http.legacy.jar.
-dontnote org.apache.http.**
-dontnote android.net.http.**

# These classes are duplicated between android.jar and core-lambda-stubs.jar.
-dontnote java.lang.invoke.**

对于第二部分，使用 aapt2 link 和 --proguard 选项。这将生成额外的必需规则，例如：

-keep class com.example.app.MainActivity { <init>(); }

必须将两组规则连同其他特定于应用程序的规则一起传递给 R8（它可以采用多个 --pg-conf 选项）。

当使用 Android Studio（更准确地说是 AGP）时，这是自动处理的。作为参考，可以在 app/build/intermediates/proguard-files 中查看这些规则。有关详细信息，请参阅 Shrink, obfuscate, and optimize your app。