[GROOVY-4759] compiler NPE with some finally blocks with explicit return

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.7.10, 1.8-rc-3, 1.9-beta-1
• Fix Version/s: 2.4.0-beta-4
• Component/s: Compiler
• Assignee: Unassigned
• Reporter: Pertino Juan
• Created: 04/Apr/11 12:30
• Updated: 17/Dec/14 13:25
• Resolved: 25/Oct/14 02:44

Description

Not normally a piece of code I would write, but a post in stackoverflow.com brought to my attention this bug.

I don't know the exact trigger, but it seems that a nested try block, with an explicit return on one of the finally clauses, when written as the final statement of a function is throwing a NullPointerException at groovyjarjarasm.asm.MethodWriter#visitMaxs

This script is the shortest example I got.

script1.groovy

try {
  try {} finally {}
} finally {
  return 0
}

Things to note:
It's the last statement of the script's run()
There is a nested try block. The blocks could be a try/catch, try/finally or try/catch/finally blocks with identical behavior
The explicit return could be anything, it will fail to compile.
There cannot be anything between the finally clauses and the end of the function.

a little bit longer

script2.groovy

try {
//  1
  try {
//    2
  } finally {
//    3
    return -1
//    4
  }
//  5
} finally {
//  6
 return -2
//  7
}
//8

There can be anything in positions 1-4,6,7
The script can be compiled when there is a statement in positions 5 or 8
Either of the explicit returns is enough, not necessarily both.

The full stacktrace is

Caught: java.lang.NullPointerException
java.lang.NullPointerException
        at org.objectweb.asm.MethodWriter.visitMaxs(Unknown Source)
        at org.objectweb.asm.MethodAdapter.visitMaxs(Unknown Source)
        at org.codehaus.groovy.classgen.AsmClassGenerator.visitConstructorOrMethod(AsmClassGenerator.java:595)
        at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitMethod(ClassCodeVisitorSupport.java:123)
        at org.codehaus.groovy.classgen.AsmClassGenerator.visitMethod(AsmClassGenerator.java:686)
        at org.codehaus.groovy.ast.ClassNode.visitContents(ClassNode.java:1039)
        at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitClass(ClassCodeVisitorSupport.java:50)
        at org.codehaus.groovy.classgen.AsmClassGenerator.visitClass(AsmClassGenerator.java:276)
        at org.codehaus.groovy.control.CompilationUnit$12.call(CompilationUnit.java:748)
        at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:942)
        at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:519)
        at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:497)
        at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:474)
        at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:306)
        at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:283)
        at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:267)
        at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:197)
        at groovy.lang.GroovyShell$2.run(GroovyShell.java:215)
        at groovy.lang.GroovyShell$2.run(GroovyShell.java:213)
        at java.security.AccessController.doPrivileged(Native Method)
        at groovy.lang.GroovyShell.run(GroovyShell.java:213)
        at groovy.lang.GroovyShell.run(GroovyShell.java:159)
        at groovy.ui.GroovyMain.processOnce(GroovyMain.java:496)
        at groovy.ui.GroovyMain.run(GroovyMain.java:311)
        at groovy.ui.GroovyMain.process(GroovyMain.java:297)
        at groovy.ui.GroovyMain.processArgs(GroovyMain.java:112)
        at groovy.ui.GroovyMain.main(GroovyMain.java:93)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.codehaus.groovy.tools.GroovyStarter.rootLoader(GroovyStarter.java:108)
        at org.codehaus.groovy.tools.GroovyStarter.main(GroovyStarter.java:130)