[PATCH 0/1] MR1390: winevulkan: Generate "in_ext" definition on demand

[Alexandros Frantzis (＠afrantzis)]

There are cases in StructConversionFunction.definition where we will
generate copy code for extension struct members, without emitting the
definition of the "in_ext" variable used in the copy code.

This issue is triggered by mismatches in the condition that guards the
generation of the "in_ext" definition, and the condition(s) that govern
the generation of the member copy code (e.g., in
StructConversionFunction.member_needs_copy and
VkMember.needs_conversion).

In order to avoid such mismatches and the burden of having to keep the
conditions in sync, this commit generates the definition on demand, by
checking if it's actually needed by the member copy code.

Signed-off-by: Alexandros Frantzis

--

Some more details in case a different solution becomes apparent.

An example of the aforementioned issue can be triggered if we make VK_EXT_image_drm_format_modifier an UNEXPOSED extension in `make_vulkan`:

```
../wine/dlls/winevulkan/vulkan_thunks.c: In function ‘convert_VkFormatProperties2_win32_to_host’:
../wine/dlls/winevulkan/vulkan_thunks.c:10214:119: error: ‘in_ext’ undeclared (first use in this function); did you mean ‘index’?
10214 |             out_ext->pDrmFormatModifierProperties = convert_VkDrmFormatModifierPropertiesEXT_array_win32_to_host(ctx, in_ext->pDrmFormatModifierProperties, in_ext->drmFormatModifierCount);
      |                                                                                                                       ^~~~~~
      |                                                                                                                       index
```

In this particular case the mismatch happens because for the `VkDrmFormatModifierPropertiesListEXT` (returnedonly=true) struct in the INPUT direction the current check doesn't emit `in_ext`:

```
if self.direction == Direction.OUTPUT or not ext.returnedonly: # Not triggered
     body += ident + "{0} *in_ext = ({0} *)in_header;\n".format(in_type)
```

but `self.member_needs_copy(ext, m)` below for the "pDrmFormatModifierProperties" member returns `True`, requiring `in_ext`. The flow is:

```
* self.member_needs_copy(ext, m) => True
   if m.name != "sType" and struct.returnedonly and not m.needs_conversion(self.conv, self.unwrap, Direction.INPUT, self.const): # Not triggered
      return False
   return True
   * m.needs_conversion(self.conv, self.unwrap, Direction.INPUT, self.const) => True
       # if pointer member needs output conversion, it also needs input conversion
       # to allocate the pointer
       if direction == Direction.INPUT and self.is_pointer() and \
          self.needs_conversion(conv, unwrap, Direction.OUTPUT, struct_const):
          return True
```