fix(loader): Write to the correct file handlers on save

Saving a ModelFile used to write back into the same FileHandler that it
was loaded from. This caused inconsistencies and unexpected behavior
when trying to change the save location at runtime by modifying
`loader.resources`. Now, ModelFiles always use the expected FileHandler.

capellambse/loader/core.py

@@ -312,28 +312,22 @@ def iterall_xt(
 
     def write_xml(
         self,
-        filename: pathlib.PurePosixPath,
+        file: t.BinaryIO,
         encoding: str = "utf-8",
     ) -> None:
         """Write this file's XML into the file specified by ``path``."""
-        LOGGER.debug("Saving tree %r to file %s", self, filename)
-        if filename.suffix in {
-            ".capella",
-            ".capellafragment",
-            ".melodyfragment",
-            ".melodymodeller",
-        }:
+        if self.fragment_type == FragmentType.SEMANTIC:
             line_length = exs.LINE_LENGTH
         else:
             line_length = sys.maxsize
-        with self.filehandler.open(filename, "wb") as file:
-            exs.write(
-                self.root,
-                file,
-                encoding=encoding,
-                line_length=line_length,
-                siblings=True,
-            )
+
+        exs.write(
+            self.root,
+            file,
+            encoding=encoding,
+            line_length=line_length,
+            siblings=True,
+        )
 
     def unfollow_href(self, element_id: str) -> etree._Element:
         """Unfollow a fragment link and return the placeholder element.
@@ -472,7 +466,7 @@ def __load_referenced_files(
             self.__load_referenced_files(ref_name)
 
     def save(self, **kw: t.Any) -> None:
-        """Save all model files back to their original locations.
+        """Save all model files.
 
         Parameters
         ----------
@@ -518,7 +512,9 @@ def save(self, **kw: t.Any) -> None:
                 if resname != "\0":
                     continue
 
-                tree.write_xml(fname)
+                LOGGER.debug("Saving tree %r to file %s", tree, fname)
+                with self.resources[resname].open(fname, "wb") as f:
+                    tree.write_xml(f)
 
     def idcache_index(self, subtree: etree._Element) -> None:
         """Index the IDs of ``subtree``.