Android早期版本实现原理请看 Android源码分析-pm命令的实现，列出包名pm list package，列出系统库pm list libraries_pm list packages-CSDN博客

Android12 对adb shell pm 实现原理做了重构：改成了template模式PackageManagerShellCommand extends ShellCommand

adb shell pm list package -3 源码：

adb shell pm 会初始化1个PackageManagerShellCommand对象，

com.android.server.pm.PackageManagerShellCommand#onCommand

final boolean isSystem = !isApex &&(info.applicationInfo.flags&ApplicationInfo.FLAG_SYSTEM) != 0;
final boolean isEnabled = !isApex && info.applicationInfo.enabled;
if ((!listDisabled || !isEnabled) &&(!listEnabled || isEnabled) &&(!listSystem || isSystem) &&(!listThirdParty || !isSystem) &&(!listApexOnly || isApex)) {pw.print("package:");

是否是3方app主要是看有没有flag：ApplicationInfo.FLAG_SYSTEM

framework已有的api：

ProcessRecord.info.isSystemApp()

android.content.pm.ApplicationInfo#isSystemApp