_dev_exposure_proxy_available finds wrong exposure instance?

Is there an existing issue for this?

• I checked and did not find my issue in the already reported ones

Describe the bug

This is used by color calibration. However, it does not find the 'main' (first) exposure instance, but rather the last instance, even if it is disabled.

Calibrating from a Color Checker chart, with an instance of exposure enabled:

Same, but with an instance of exposure added (above the previous one), and then disabled:

Maybe modify exposure reading functions like this? In order to avoid repetition, this could be refactored to find the first instance in a separate function, and functions using it could just check if the instance was found, and if yes, call dev->proxy.whatever_function(module).

  if (dt_view_get_current() != DT_VIEW_DARKROOM) return 0.0f;

  // The proxy function pointers are only set if an exposure module has been initialized.
  if (!dev->proxy.exposure.whatever_function) return 0.0f;

  for (GList *l = dev->iop; l; l = g_list_next(l))
  {
    dt_iop_module_t *module = (dt_iop_module_t *)l->data;

    if (module->enabled && dt_iop_module_is(module->so, "exposure"))
    {
      return dev->proxy.whatever_function(module);
    }
  }

Steps to reproduce

See above

Expected behavior

darktable should use the 1st enabled instance (probably)

Logfile | Screenshot | Screencast

No response

Commit

No response

Where did you obtain darktable from?

darktable.org / GitHub release

darktable version

684779a88d529 (current master)

What OS are you using?

Linux

What is the version of your OS?

OS-independent

Describe your system

No response

Are you using OpenCL GPU in darktable?

None

If yes, what is the GPU card and driver?

No response

Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip

No response

Start by locating _dev_exposure_proxy_available and the exposure reading functions that use it, then reproduce the Color Checker calibration case with multiple exposure instances, including a disabled one. Trace how the exposure instances are selected and verify that darktable uses the first enabled instance consistently; the issue is done when the reported calibration behavior matches that expectation.