supported files stop being `--watch`ed if they fail to load

[snoyer]

Describe the bug When a file of a supported type opened with the --watch option is overridden with erroneous data, overriding it again with a correct model does not trigger a reload automatically (but pressing the up key does).

To Reproduce Steps to reproduce the behavior:

1. run following python script to create and periodically override watched.off in your temp directory

from time import sleep
from pathlib import Path
from tempfile import gettempdir

fn = Path(gettempdir()) / "watched.off"
delay = 3

while True:
    for name, off in {
        "a tetrahedron": "OFF\n4 4 0\n1 1 1\n1 -1 -1\n-1 1 -1\n-1 -1 1\n3 1 2 0\n3 0 2 3\n3 3 2 1\n3 1 0 3",
        "a cube": "OFF\n8 6 0\n-1 -1 -1\n-1 -1 1\n-1 1 -1\n-1 1 1\n1 -1 -1\n1 -1 1\n1 1 -1\n1 1 1\n4 0 1 3 2\n4 6 7 5 4\n4 5 7 3 1\n4 0 2 6 4\n4 4 5 1 0\n4 3 7 6 2",
        "broken": "OFF\n4 1 0\n1 1 1\n1 -1 -1\n-1 1 -1\n-1 -1 1\n0",
    }.items():
        fn.write_text(off)
        print(f"{fn} is now {name}")
        sleep(delay)

2. open the file with f3d --watch /tmp/watched.off
3. observe the file does reload when changing from a tetrahedron to a cube to a broken file
4. observe the file does not reload as a tetrahedron after being broken, press up to reload manually

Expected behavior The file should reload every time even after it failed to load

System Information: N/A

F3D Information 3.0, 3.1

Additional context The bug is due to supported files that fail to load being treated as unsupported.

The following diff could be the base of a quick and dirty fix as it does allow the broken file to reload automatically:

diff --git a/application/F3DStarter.cxx b/application/F3DStarter.cxx
index 9b76ea17..37facf28 100644
--- a/application/F3DStarter.cxx
+++ b/application/F3DStarter.cxx
@@ -1456,10 +1456,6 @@ void F3DStarter::LoadFileGroup(
             "Loading animation time: ", this->Internals->AppOptions.AnimationTime.value());
           scene.loadAnimationTime(this->Internals->AppOptions.AnimationTime.value());
         }
-
-        // Update loaded files
-        std::copy(
-          localPaths.begin(), localPaths.end(), std::back_inserter(this->Internals->LoadedFiles));
       }
     }
   }
@@ -1473,6 +1469,9 @@ void F3DStarter::LoadFileGroup(
     unsupported = true;
   }
 
+  // Update loaded files
+  std::copy(localPaths.begin(), localPaths.end(), std::back_inserter(this->Internals->LoadedFiles));
+
   std::string filenameInfo;
   if (this->Internals->LoadedFiles.size() > 0)
   {
@@ -1549,7 +1548,7 @@ void F3DStarter::LoadFileGroup(
   // but there is no way to detect if an option has been set
   // by the user or not.
   f3d::options& options = this->Internals->Engine->getOptions();
-  options.ui.dropzone = this->Internals->LoadedFiles.empty();
+  options.ui.dropzone = unsupported;
   options.ui.filename_info = filenameInfo;
 }

However a proper solution would involve distinguishing between actually unsupported files and supported files that failed to load to be able to act accordingly (logging, UI, ...).

[mwestphal]

Indeed this usecase was not considered at all. good catch!