[Issue 19381] New: capture pointer in nested function should not be called "this"

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19381

          Issue ID: 19381
           Summary: capture pointer in nested function should not be
                    called "this"
           Product: D
           Version: D2
          Hardware: All
                OS: Windows
            Status: NEW
          Keywords: symdeb
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: r.sagitario at gmx.de

struct Struct
{
        int x = 3;
        int foo()
        {
                int y = 5;
                int nested()
                {
                        int z = 7;
                        return x + y + z;
                }
                return nested();
        }
}

int main()
{
   return Struct().foo();
}

When compiled with -g, this shows a variable in nested() called "this", but is
not the struct, but the capture of the outer function:

(00004C) S_GPROC32: [0000:00000000], Cb: 0000002B, Type:             0x1004,
dg.Struct.foo.nested
         Parent: 00000000, End: 00000000, Next: 00000000
         Debug start: 0000000C, Debug end: 00000026

(000088)  S_REGREL32: rbp+00000010, Type:             0x1019, this
(0000A0)  S_ENDARG
(0000A4)  S_REGREL32: rbp+FFFFFFF8, Type:       T_INT4(0074), z

(0000B4) S_END

The type of "this" used to be void*, but has recently been populated with the
captured stack variables of the outer function:

0x1016 : Length = 42, Leaf = 0x1505 LF_STRUCTURE
        # members = 2,  field list type 0x1017, 
        Derivation list type 0x0000, VT shape type 0x0000
        Size = 0, class name = CAPTURE.dg.Struct.foo

0x1017 : Length = 34, Leaf = 0x1203 LF_FIELDLIST
        list[0] = LF_MEMBER, public, type = 0x1015, offset = 16
                member name = 'this'
        list[1] = LF_MEMBER, public, type = 0x1002, offset = (LF_SHORT) -8
                member name = 'y'

0x1019 : Length = 10, Leaf = 0x1002 LF_POINTER
        Pointer (__ptr64), Size: 8
        Element type : 0x1016

Note the "this" member of the capture struct. Having multiple "this" variables
confuses both the debugger and the user.

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