使用 scala 宏时，为什么编译错误堆栈跟踪看起来如此不连贯?

Question

我想在一些不可靠的宏上试验scala。所以我模仿了无形调用中的一个简单的错误：

import shapeless.Witness
val v = Witness(Random.nextInt())

然后我用gradle build --info --stacktrace编译它，期望找到一个以"无形"开头的异常。证人"或类似的东西。相反，我得到了这个：

> Task :common:compileTestScala
[Error] /home/peng/git-spike/scalaspike/common/src/test/scala/com/tribbloids/spike/shapeless_spike/RefinedType/Creation.scala:12: Expression scala.util.Random.nextInt() does not evaluate to a constant or a stable reference value
one error found
> Task :common:compileTestScala FAILED
5 actionable tasks: 1 executed, 4 up-to-date
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':common:compileTestScala'.
> Compilation failed
* Try:
Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':common:compileTestScala'.
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.lambda$executeIfValid$1(ExecuteActionsTaskExecuter.java:205)
at org.gradle.internal.Try$Failure.ifSuccessfulOrElse(Try.java:263)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeIfValid(ExecuteActionsTaskExecuter.java:203)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:184)
at org.gradle.api.internal.tasks.execution.CleanupStaleOutputsExecuter.execute(CleanupStaleOutputsExecuter.java:114)
at org.gradle.api.internal.tasks.execution.FinalizePropertiesTaskExecuter.execute(FinalizePropertiesTaskExecuter.java:46)
at org.gradle.api.internal.tasks.execution.ResolveTaskExecutionModeExecuter.execute(ResolveTaskExecutionModeExecuter.java:62)
at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:57)
at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:56)
at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:36)
at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.executeTask(EventFiringTaskExecuter.java:77)
at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.call(EventFiringTaskExecuter.java:55)
at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.call(EventFiringTaskExecuter.java:52)
at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:416)
at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:406)
at org.gradle.internal.operations.DefaultBuildOperationExecutor$1.execute(DefaultBuildOperationExecutor.java:165)
at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:250)
at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:158)
at org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:102)
at org.gradle.internal.operations.DelegatingBuildOperationExecutor.call(DelegatingBuildOperationExecutor.java:36)
at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter.execute(EventFiringTaskExecuter.java:52)
at org.gradle.execution.plan.LocalTaskNodeExecutor.execute(LocalTaskNodeExecutor.java:41)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:372)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:359)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:352)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:338)
at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.lambda$run$0(DefaultPlanExecutor.java:127)
at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.execute(DefaultPlanExecutor.java:191)
at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.executeNextNode(DefaultPlanExecutor.java:182)
at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.run(DefaultPlanExecutor.java:124)
at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)
at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)
Caused by: org.gradle.api.internal.tasks.compile.CompilationFailedException: Compilation failed
at org.gradle.api.internal.tasks.scala.ZincScalaCompiler.execute(ZincScalaCompiler.java:151)
at org.gradle.api.internal.tasks.scala.ZincScalaCompilerFacade.execute(ZincScalaCompilerFacade.java:47)
at org.gradle.api.internal.tasks.scala.ZincScalaCompilerFacade.execute(ZincScalaCompilerFacade.java:32)
at org.gradle.api.internal.tasks.compile.daemon.AbstractDaemonCompiler$CompilerWorkAction.execute(AbstractDaemonCompiler.java:135)
at org.gradle.workers.internal.DefaultWorkerServer.execute(DefaultWorkerServer.java:63)
at org.gradle.workers.internal.AbstractClassLoaderWorker$1.create(AbstractClassLoaderWorker.java:47)
at org.gradle.workers.internal.AbstractClassLoaderWorker$1.create(AbstractClassLoaderWorker.java:41)
at org.gradle.internal.classloader.ClassLoaderUtils.executeInClassloader(ClassLoaderUtils.java:98)
at org.gradle.workers.internal.AbstractClassLoaderWorker.executeInClassLoader(AbstractClassLoaderWorker.java:41)
at org.gradle.workers.internal.IsolatedClassloaderWorker.execute(IsolatedClassloaderWorker.java:49)
at org.gradle.workers.internal.WorkerDaemonServer.execute(WorkerDaemonServer.java:84)
at org.gradle.process.internal.worker.request.WorkerAction$1.call(WorkerAction.java:129)
at org.gradle.process.internal.worker.child.WorkerLogEventListener.withWorkerLoggingProtocol(WorkerLogEventListener.java:41)
at org.gradle.process.internal.worker.request.WorkerAction.run(WorkerAction.java:126)
at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:182)
at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:164)
at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:412)
... 3 more
Caused by: Compilation failed
at sbt.internal.inc.AnalyzingCompiler.call(AnalyzingCompiler.scala:253)
at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:122)
at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:95)
at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:91)
at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
at sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:186)
at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$3(MixedAnalyzingCompiler.scala:82)
at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$3$adapted(MixedAnalyzingCompiler.scala:77)
at sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:215)
at sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:77)
at sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:146)
at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:343)
at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:343)
at sbt.internal.inc.Incremental$.doCompile(Incremental.scala:120)
at sbt.internal.inc.Incremental$.$anonfun$compile$4(Incremental.scala:100)
at sbt.internal.inc.IncrementalCommon.recompileClasses(IncrementalCommon.scala:180)
at sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:98)
at sbt.internal.inc.Incremental$.$anonfun$compile$3(Incremental.scala:102)
at sbt.internal.inc.Incremental$.manageClassfiles(Incremental.scala:155)
at sbt.internal.inc.Incremental$.compile(Incremental.scala:92)
at sbt.internal.inc.IncrementalCompile$.apply(Compile.scala:75)
at sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:348)
at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:301)
at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:168)
at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:248)
at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:74)
at org.gradle.api.internal.tasks.scala.ZincScalaCompiler.execute(ZincScalaCompiler.java:147)
... 21 more

这应该如何帮助我？我只能看到shapeless.Witness的代码，而不是整个sbt.internal.inc.AnalyzingCompiler。我应该怎么做才能看到可能与实际报告错误的宏相关的错误？

更新 1我代表 Dmytro Mitin 还想附加我的构建配置：

allprojects {
apply(plugin = "java")
apply(plugin = "java-library")
apply(plugin = "scala")
...
dependencies {
implementation("org.scala-lang:scala-compiler:${vs.scalaV}")
implementation("org.scala-lang:scala-library:${vs.scalaV}")
implementation("org.scala-lang:scala-reflect:${vs.scalaV}")
<vs.scalaV=2.12.11>
... 
<witness is introduced in s submodule>
}
tasks {
val jvmTarget = JavaVersion.VERSION_1_8.toString()
withType<ScalaCompile> {
targetCompatibility = jvmTarget
scalaCompileOptions.loggingLevel = "debug"
scalaCompileOptions.additionalParameters = listOf(
"-encoding", "utf8",
"-unchecked",
"-deprecation",
"-feature",
"-Xfatal-warnings",
"-Xlog-implicits",
"-Yissue-debug"
)
}
}
}

关于 maven 的更新 2：

[ERROR] /home/peng/git-dev/scala-2.11/datapassports/spookystuff/core/src/test/scala/com/tribbloids/spookystuff/utils/WitnessSpike.scala:11: Expression scala.util.Random.nextInt() does not evaluate to a constant or a stable reference value
[ERROR]   Witness(Random.nextInt())
[ERROR]          ^
...
[ERROR] Failed to execute goal net.alchim31.maven:scala-maven-plugin:3.4.6:testCompile (scala-test-compile-first) on project spookystuff-core: Execution scala-test-compile-first of goal net.alchim31.maven:scala-maven-plugin:3.4.6:testCompile failed.: CompileFailed -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal net.alchim31.maven:scala-maven-plugin:3.4.6:testCompile (scala-test-compile-first) on project spookystuff-core: Execution scala-test-compile-first of goal net.alchim31.maven:scala-maven-plugin:3.4.6:testCompile failed.
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:190)
at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:186)
at java.util.concurrent.FutureTask.run (FutureTask.java:266)
at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:511)
at java.util.concurrent.FutureTask.run (FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:624)
at java.lang.Thread.run (Thread.java:748)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution scala-test-compile-first of goal net.alchim31.maven:scala-maven-plugin:3.4.6:testCompile failed.
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:148)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:190)
at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:186)
at java.util.concurrent.FutureTask.run (FutureTask.java:266)
at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:511)
at java.util.concurrent.FutureTask.run (FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:624)
at java.lang.Thread.run (Thread.java:748)
Caused by: sbt.compiler.CompileFailed
at sbt.compiler.AnalyzingCompiler.call (AnalyzingCompiler.scala:111)
at sbt.compiler.AnalyzingCompiler.compile (AnalyzingCompiler.scala:53)
at sbt.compiler.AnalyzingCompiler.compile (AnalyzingCompiler.scala:47)
at sbt.compiler.AggressiveCompile$$anonfun$3$$anonfun$compileScala$1$1.apply$mcV$sp (AggressiveCompile.scala:95)
at sbt.compiler.AggressiveCompile$$anonfun$3$$anonfun$compileScala$1$1.apply (AggressiveCompile.scala:95)
at sbt.compiler.AggressiveCompile$$anonfun$3$$anonfun$compileScala$1$1.apply (AggressiveCompile.scala:95)
at sbt.compiler.AggressiveCompile.sbt$compiler$AggressiveCompile$$timed (AggressiveCompile.scala:168)
at sbt.compiler.AggressiveCompile$$anonfun$3.compileScala$1 (AggressiveCompile.scala:94)
at sbt.compiler.AggressiveCompile$$anonfun$3.apply (AggressiveCompile.scala:142)
at sbt.compiler.AggressiveCompile$$anonfun$3.apply (AggressiveCompile.scala:84)
at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply (Compile.scala:66)
at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply (Compile.scala:64)
at sbt.inc.IncrementalCommon.cycle (IncrementalCommon.scala:32)
at sbt.inc.Incremental$$anonfun$1.apply (Incremental.scala:72)
at sbt.inc.Incremental$$anonfun$1.apply (Incremental.scala:71)
at sbt.inc.Incremental$.manageClassfiles (Incremental.scala:99)
at sbt.inc.Incremental$.compile (Incremental.scala:71)
at sbt.inc.IncrementalCompile$.apply (Compile.scala:54)
at sbt.compiler.AggressiveCompile.compile2 (AggressiveCompile.scala:159)
at sbt.compiler.AggressiveCompile.compile1 (AggressiveCompile.scala:68)
at com.typesafe.zinc.Compiler.compile (Compiler.scala:207)
at com.typesafe.zinc.Compiler.compile (Compiler.scala:189)
at com.typesafe.zinc.Compiler.compile (Compiler.scala:180)
at com.typesafe.zinc.Compiler.compile (Compiler.scala:171)
at sbt_inc.SbtIncrementalCompiler.compile (SbtIncrementalCompiler.java:94)
at scala_maven.ScalaCompilerSupport.incrementalCompile (ScalaCompilerSupport.java:320)
at scala_maven.ScalaCompilerSupport.compile (ScalaCompilerSupport.java:136)
at scala_maven.ScalaCompilerSupport.doExecute (ScalaCompilerSupport.java:116)
at scala_maven.ScalaMojoSupport.execute (ScalaMojoSupport.java:574)
at scala_maven.ScalaTestCompileMojo.execute (ScalaTestCompileMojo.java:50)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:190)
at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:186)
at java.util.concurrent.FutureTask.run (FutureTask.java:266)
at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:511)
at java.util.concurrent.FutureTask.run (FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:624)
at java.lang.Thread.run (Thread.java:748)

哎呀，同样没用。简直不敢相信我对此寄予厚望。Relevenat构建插件配置如下所示：

<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.4.6</version>
<executions>
<execution>
<id>scala-compile-first</id>
<phase>process-resources</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
<execution>
<id>scala-test-compile-first</id>
<phase>process-test-resources</phase>
<goals>
<goal>testCompile</goal>
</goals>
</execution>
<!--required for publishing to maven central-->
<execution>
<id>add-source</id>
<goals>
<goal>add-source</goal>
</goals>
</execution>
<execution>
<id>attach-scaladocs</id>
<goals>
<goal>doc-jar</goal>
</goals>
<configuration>
<args>
<!--                see https://github.com/dmlc/xgboost/issues/4000-->
<arg>-nobootcp</arg>
</args>
</configuration>
</execution>
</executions>
<configuration>
<scalaVersion>${scala.version}</scalaVersion>
<scalaCompatVersion>${scala.binary.version}</scalaCompatVersion>
<recompileMode>incremental</recompileMode>
<!--https://tpolecat.github.io/2017/04/25/scalac-flags.html-->
<args>
<arg>-target:jvm-${java.version}</arg>
<arg>-unchecked</arg>
<arg>-deprecation</arg>
<arg>-feature</arg>
<arg>-g:vars</arg>
<arg>-encoding</arg>
<arg>UTF-8</arg>
<arg>-Xlint</arg>
</args>
<javacArgs>
<javacArg>-source</javacArg>
<javacArg>${java.version}</javacArg>
<javacArg>-target</javacArg>
<javacArg>${java.version}</javacArg>
</javacArgs>
<excludes>
<exclude>**/.ipynb_checkpoints/*</exclude>
</excludes>
</configuration>
</plugin>

更新 3我终于尝试了 sbt，但显然无法启用宏堆栈跟踪选项。这是 sbt 构建文件中的 scalac 配置：

scalacOptions ++= Seq(
"-unchecked",
"-deprecation",
"-feature",
//                            "-Xfatal-warnings",
"-Xlint:poly-implicit-overload",
"-Xlint:option-implicit",
//  "-Xlog-implicits",
//  "-Xlog-implicit-conversions",
"-Yissue-debug"
)
scalacOptions in (Compile, doc) ++= Seq("-groups")
/** Enable for debugging */
testOptions in Test += Tests.Argument("-oF")

然后它显示的信息甚至比maven&gradle还要少：

> run
[warn] Credentials file /home/peng/.bintray/.credentials does not exist
[warn] Credentials file /home/peng/.ivy2/.sbtcredentials does not exist
[info] Compiling 235 Scala sources and 30 Java sources to /home/peng/git-release/spark-nlp/target/scala-2.11/classes...
[error] /home/peng/git-release/spark-nlp/src/main/scala/com/johnsnowlabs/collections/SearchTrie.scala:86: Expression scala.util.Random.nextInt() does not evaluate to a constant or a stable reference value
[error]   Witness(Random.nextInt())
[error]          ^
[warn] /home/peng/git-release/spark-nlp/src/main/scala/com/johnsnowlabs/ml/tensorflow/TensorflowSpell.scala:134: inferred existential type (org.tensorflow.Tensor[?0], org.tensorflow.Tensor[?0], org.tensorflow.Tensor[?0]) forSome { type ?0; type ?0; type ?0 }, which cannot be expressed by wildcards,  should be enabled
... (skipping irrelevant warnings)
[warn] 9 warnings found
[error] one error found
[error] (compile:compileIncremental) Compilation failed
[error] Total time: 5 s, completed 28-Jul-2020 12:44:30 AM
> 
> 
> 
> last run
> 
> 

我是否错过了这些构建系统中的某些内容？

Answer 1

其他编译器错误是否为您提供了有用的堆栈跟踪？

堆栈跟踪基本上是一个运行时的东西：编译时唯一可以拥有的堆栈跟踪是编译器中的堆栈跟踪(例如，问题中堆栈跟踪中的sbt.compiler包(。

通常，若要调试宏问题，根据问题，你将执行以下操作之一：

• 在调试器中运行 Scala 编译器(有说明(，如果有问题的宏无法展开
• 使用-Ymacro-debug-lite编译器选项转储生成的代码，该选项将为您提供生成的 Scala 代码和抽象语法树表示形式;这仅在宏扩展但自身无法编译或表现出运行时错误的情况下有用