calling a function inside visual D debugger: partially possible, want better support

[Rainer Schuetze]

On 10/20/2012 12:53 AM, timotheecour wrote:
> short version:
> how to call a (non extern-C) function from visualD's debugger? ( I can
> do it with extern C)
> how to call a function with arguments that are stack variables (I can do
> it with actual numeric values, eg actual pointer addresses)
>
> long version:
>
> when debugging a session inside visual D, it can be very useful to call
> functions directly, eg:
>
> * to print variables that visual D doesn't display properly (such as
> dynamic arrays, where visualD just prints the length and pointer)
>
> * for interactive purposes (eg trying a function with different parameters)
>
> Currently, visualD's support for this is limited, but I was able to do
> certain useful things (I'm not sure if many people realized one can do
> this in visuald, but this can be useful):

I know it's possible and I use it in C++ from time to time, but never 
tried it in D.

>
> suppose we compile a D program into Main.exe:
> we can call extern(C) functions as follows, by adding a watch variable
> in visual studio debugger and entering in the name field:
> Main.exe!main_test at test1(2)
> => will show value=25, type=int, and will print in the command prompt
> "res=25"
>
> now get address of z1 by looking into "Locals":
> it shows:
> -        z1    {length=4 ptr=0x01f20f40 {1} }    int[]
> then display the dynamic array z1:
> Main.exe!main_test at writelnPtr(3,0x01f20f40)
>
> This is nice but not very convenient. Is there a way (if not, can that
> be addressed in the near future) to support the following?

VS2012 allows "main_test at writelnPtr(z1.length,z1.ptr)"

Actually, the changes to autoexp.dat that are done by the installer are 
supposed to display dynamic and associative arrays, but it seems they 
are broken in VS2012 and maybe also 2010.

>
> * Main.exe!main_test at writeln2(z1)
> =>currently returns: identifier "z1" is undefined

VS2012 says: "Passing class, struct or union types by value to a 
function evaluation is not supported". It works if you pass the argument 
by reference.

>
> * Main.exe!main_test at writeln2([1,2,3])
> =>currently returns: expected a type specifier

The VS debugger expects C/C++ syntax, so it cannot do this.


>
> * Main.exe!main_test at writeln3()
> =>currently returns: identifier "main_test at writeln3" is undefined

If you disable name demangling by cv2pdb, the symbol 
_D9main_test8writeln3FZv resolves to the function writeln3, but 
unfortunately its type is reported as "void*". I guess the VS debugger 
does not allow the calling convention used by D in function evaluation.

If you use mago as the debug engine, you will get better D expression 
support and output, but it is not capable of running functions through 
watch expressions. Unfortunately development of mago seems to have 
stopped/paused. Nevertheless, I think a dedicated debug engine is the 
way to go for the best user experience.