TODO #1069

Error handling statement (1%) was converted to a complex pattern which might not be equivalent to the original.

Description

This ussually occurs when a Resume Next Error Handling Pattern appears. It is a warning because functional equivalence could not be accomplished in this scenario.

Recommendations

The Resume Next error handling pattern resumes execution of the next statement after an error. In the case of structured error handling, the resulting behavior is more similar to an On Error Go To statement, where the catch statement serves as the Go To label.

For this reason the replacement done by the VB6 AI Migrator might not be the exact funcional equivalent of the original code. In cases where the code is related, meaning if one call fails subsequent calls are likely to fail, then leaving a single try / catch statement could work. Since an error at any point of the process would merely be replicated in the susbsequent.

A common example of this might be file operations, generally if the IO operation fails at the beginning, all subsequent calls will fail.

In other cases, the error pattern of Resume Next is necessary when the code statements are fairly independent a failure in one statement does not affect the error condition of a subsequent call. The code sample illustrate such a case. In order to ensure functional equivalence it's necessary to add a try catch (with empty clause) to each line that can throw an exception. In these cases the main try catch (generated by the VB6 AI Migrator) is less effective and should be removed.

Sample VB6

PublicFunction ComplexErrorPattern() AsInteger

F1(1)

OnErrorResumeNext

Dim I AsInteger

I = 0

I = F2(1)

If I <> 0 Then

I = F4(80)

Else

I = F3(50)

EndIf

Exit_Label:

ComplexErrorPattern = I

ExitFunction

EndFunction

Target VB.NET

PublicFunction ComplexErrorPattern() AsInteger

F1(1)

'UPGRADE_TODO: (1069) Error handling statement (On Error Resume Next) was converted to a complex pattern which might not be equivalent to the original.

Try

Dim I AsInteger = 0

I = F2(1)

If I <> 0 Then

I = F4(80)

Else

I = F3(50)

EndIf

Return I

Catch exc As System.Exception

ThrowNew Exception("Migration Exception: The following exception could be handled in a different way after the conversion: " + exc.Message)

EndTry

EndFunction

Expected VB.NET

PublicFunction ComplexErrorPattern() AsInteger

Dim I AsInteger = 0

Try

I = F1(1)

Catch

EndTry

If I <> 0 Then

Try

I = F2(80)

Catch

EndTry

Else

Try

I = F3(50)

Catch

EndTry

EndIf

Return I

EndFunction

Target C#

publicint ComplexErrorPattern()

{

F1(1);

//UPGRADE_TODO: (1069) Error handling statement (On Error Resume Next) was converted to a complex pattern which might not be equivalent to the original.

try

{

int I = 0;

I = F2(1);

if (I != 0)

{

I = F4(80);

}

else

{

I = F3(50);

}

return I;

}

catch (Exception exc)

{

thrownew Exception("Migration Exception: The following exception could be handled in a different way after the conversion: " + exc.Message);

}

return 0;

}

In this case it may be necessary to add a try catch block for the call to F2, F3 and F4, if the function can throw an exception.

Expected C#

staticpublicint ComplexErrorPattern()

{

int I = 0;

try

{

I = F1(1);

}

catch

{

}

if (I != 0)

{

try

{

I = F2(80);

}

catch

{

}

}

else

{

try

{

I = F3(50);

}

catch

{

}

}

return I;

}