[Mono-bugs] [Bug 605340] New: Unexpected exception on calling String.LastIndexOf on empty strings with startIndex=-1

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http://bugzilla.novell.com/show_bug.cgi?id=605340

http://bugzilla.novell.com/show_bug.cgi?id=605340#c0


           Summary: Unexpected exception on calling String.LastIndexOf on
                    empty strings with startIndex=-1
    Classification: Mono
           Product: Mono: Class Libraries
           Version: SVN
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: CORLIB
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: lorenz.schwittmann at gmail.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---
           Blocker: ---


User-Agent:       Mozilla/5.0 (X11; U; Linux x86_64; de; rv:1.9.2.3)
Gecko/20100423 Ubuntu/10.04 (lucid) Firefox/3.6.3

I just encountered a reproducible crash in an application which runs fine on
Microsoft's .NET. After some debugging, I isolated the problem in the following
call:

String str = "";
str.LastIndexOf('.', -1);

Microsoft's documentation
(http://msdn.microsoft.com/en-us/library/1tw91fa3%28v=VS.100%29.aspx) says, the
method will throw an exception if the second parameter is greater than
this.Length. However, there seems to be a check at the top of the function
which returns -1 if this.Length ==0. No exception is thrown in their
implementation.

Reproducible: Always

Steps to Reproduce:
1. Compile a test application which contains "".LastIndexOf('.', -1);
2. Run application on both mono and MS .NET
Actual Results:  
The application crashes only on mono.

Expected Results:  
The application shouldn't crash.
Although MS lies in their specs, mono's goal should be to be as close as
possible to their implementation. Otherwise the "write once, run everywhere"
argument is invalid.

I've found a similar bug report
(https://bugzilla.novell.com/show_bug.cgi?id=486234) which deals with an
overloaded version of String.LastIndexOf. However, the committed fix does only
care about calls with startIndex == 0.

I have verified that there is no exception on calling on an empty string with
startIndex=-1 for the following signatures:

String.LastIndexOf(String, Int32)
String.LastIndexOf(Char, Int32, Int32)
String.LastIndexOf(String, Int32, Int32)
String.LastIndexOf(String, Int32, StringComparison)
String.LastIndexOf(String, Int32, Int32, StringComparison)

I suggest to fix ALL of them: If the string is empty, return -1. No matter what
other arguments are passed.

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