'Step in' in JMC mode may skip user code on .NET 4.5.2

[dgrunwald]

• Create a C# console application
• Ensure the 'just my code' debugger option is enabled
• Use the following program code:

using System;
using System.Diagnostics;

class Program
{
    [DebuggerStepThrough]
    static void StepRoot()
    {
        IgnoredClass.StepLeft();
        StepRight();
    }

    [DebuggerNonUserCode]
    public class IgnoredClass {
        public static void StepLeft() {}
    }

    static void StepRight() {}


    public static void Main(string[] args)
    {
        StepRoot();
    }
}

• Place a breakpoint on 'StepRoot()' in the main method.
• Run the program
• Use F11 to step into the method call.

Expected result: the debugger steps into StepRight, as that is the first method called by StepRoot() which isn't supposed to be skipped.

Running SharpDevelop on .NET 4.5.1, this works as expected. But on .NET 4.5.2, the actual result is: the debugger steps over the whole StepRoot() call.

This is the ControlFlow_Stepping debugger unit test.

[dgrunwald]

This is the debug log for the stepping process on .NET 4.5.1:

Debugger: Debugger event: OnResumed()
Debugger: Callback: StepComplete (STEP_CALL)
Debugger:  - stopped at Debugger.Tests.ControlFlow_Stepping.StepRoot because of StepIn from [Method Debugger.Tests.ControlFlow_Stepping.Main():System.Void] name="normal"
Debugger:  - method Debugger.Tests.ControlFlow_Stepping.StepRoot marked as non user code
Debugger:  - seeking user code
Debugger: Callback: StepComplete (STEP_CALL)
Debugger:  - stopped at Debugger.Tests.ControlFlow_Stepping.IgnoredClass.StepLeft because of StepIn from [Method Debugger.Tests.ControlFlow_Stepping.StepRoot():System.Void] name="seeking user code"
Debugger:  - method Debugger.Tests.ControlFlow_Stepping.IgnoredClass.StepLeft marked as non user code
Debugger:  - seeking user code
Debugger: Callback: StepComplete (STEP_CALL)
Debugger:  - stopped at Debugger.Tests.ControlFlow_Stepping.StepRight because of StepIn from [Method Debugger.Tests.ControlFlow_Stepping+IgnoredClass.StepLeft():System.Void] name="seeking user code"
Debugger:  - pausing in user code
Debugger: Debugger event: OnPaused()

and here is the same for the stepping process in .NET 4.5.2:

Debugger: Debugger event: OnResumed()
Debugger: Callback: StepComplete (STEP_CALL)
Debugger:  - stopped at Debugger.Tests.ControlFlow_Stepping.StepRoot because of StepIn from [Method Debugger.Tests.ControlFlow_Stepping.Main():System.Void] name="normal"
Debugger:  - method Debugger.Tests.ControlFlow_Stepping.StepRoot marked as non user code
Debugger:  - seeking user code
Debugger: Callback: StepComplete (STEP_CALL)
Debugger:  - stopped at Debugger.Tests.ControlFlow_Stepping.IgnoredClass.StepLeft because of StepIn from [Method Debugger.Tests.ControlFlow_Stepping.StepRoot():System.Void] name="seeking user code"
Debugger:  - method Debugger.Tests.ControlFlow_Stepping.IgnoredClass.StepLeft marked as non user code
Debugger:  - seeking user code
Debugger: Callback: StepComplete (STEP_RETURN)
Debugger:  - stopped at Debugger.Tests.ControlFlow_Stepping.Main because of StepIn from [Method Debugger.Tests.ControlFlow_Stepping+IgnoredClass.StepLeft():System.Void] name="seeking user code"
Debugger:  - finishing step in
Debugger: Callback: StepComplete (STEP_NORMAL)
Debugger:  - stopped at Debugger.Tests.ControlFlow_Stepping.Main because of StepIn from [Method Debugger.Tests.ControlFlow_Stepping.Main():System.Void] name="finishing step in"
Debugger:  - pausing in user code
Debugger: Debugger event: OnPaused()

[dgrunwald]

As can be seen in the step logs above, both .NET 4.5.1 and 4.5.2 work as follows:

• The debugger steps into StepMain(), and stops there
• SharpDevelop notices the attribute, marks the method as user-code (JMC status false), and continues single-stepping
• Then the same happens with StepLeft()

In .NET 4.5.1, this brings us from StepLeft() to StepRight(), but on .NET 4.5.2 it brings us from StepLeft() directly back to Main().

Note that this bug only happens the first time (when the JMC status for those methods is not initialized yet). If the Main() method is modified to call StepRoot() twice, the first time trying to step into the method will step over it, but the second time will work fine and step into StepRight.