[jboss-jira] [JBoss JIRA] (JASSIST-210) MethodCall.replace() throws inconsistent stack height in certain scenarios

[Patson Luk (JIRA)]

    [ https://issues.jboss.org/browse/JASSIST-210?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12934579#comment-12934579 ] 

Patson Luk commented on JASSIST-210:
------------------------------------

Many thanks for the detailed reply!

There is still one piece that I do not quite understand, would please please kindly elaborate?

You mentioned that after the translation 2 and 3 are replaced with a try-catch statement, but in the sample code, the replacement block $_ = $proceed($$) itself is NOT surrounded by try-catch, only the injected System.out... was surrounded by try-catch:

 "{ try
{ System.out.println(\"injected\"); }

catch (Exception e)
{ e.printStackTrace(); }

$_ = $proceed($$); }";

Therefore, if $_ = $proceed($$) does throw exception, it should still follow the same flow as if there is no try-catch? (as that piece of the code is not really wrapped)

Many thanks for your clarification in advanced
                
> MethodCall.replace() throws inconsistent stack height in certain scenarios
> --------------------------------------------------------------------------
>
>                 Key: JASSIST-210
>                 URL: https://issues.jboss.org/browse/JASSIST-210
>             Project: Javassist
>          Issue Type: Bug
>    Affects Versions: 3.16.1-GA, 3.18.1-GA
>            Reporter: Patson Luk
>            Assignee: Shigeru Chiba
>
> Tested on 3.16.1-GA
> This is similar to https://issues.jboss.org/browse/JASSIST-52, but the try-catch block usage is different (not wrapping the $proceed($$))
> Based on the javassist tutorial,  the substituted code for MethodCall.replace():
> {{Note that the substituted code is not an expression but a statement or a block. It cannot be or contain a try-catch statement.}}
> However in the case that try-catch does not wrap the $_=$proceed($$);
> It seems to work properly. For example:
> ctClass.instrument(new ExprEditor() {
>     public void edit(MethodCall m) throws CannotCompileException {
>         if (m.getMethodName().equals("testMethod2")) {
>             String newBlock = "{ try { System.out.println(\"injected\"); } catch (Exception e) { e.printStackTrace(); } $_ = $proceed($$); }";
>             m.replace(newBlock);
>         }
>     }
> });
> {{which ctClass is class TestReplace, which has code as below:}}
> public class TestReplace {
>     public static void main(String[] args) {
>         RefClass ref = new RefClass();
>         ref.testMethod2();
>     }
> }
> class RefClass {
>     public void testMethod1(Object o) {}
>     public Object testMethod2() { return null; }
> }
> {{running TestReplace with the modified bytecode correctly prints "injected" to the screen. However if I add one more line to the TestReplace's main() method}}
> ref.testMethod1(ref.testMethod2());
> {{It throws exception as below}}
> javassist.bytecode.BadBytecode: inconsistent stack height -1
> javassist.bytecode.stackmap.Tracer.doOpcode(Tracer.java:106)
> *So is try-catch acceptable if it does not wrap the $_=$proceed($$)? If so, is it a bug if it does not work properly for method invocation within another method invocation?*
> Many thanks in advance!

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