Pass through resolve_path when the path is not accessible (cctbx#772)

* Resolve path only if accessible, otherwise return unchanged. Fixes cctbx#771
* Given that we're already monkeypatching in the test, use this to also fake out os.path.exists to get the old behaviour for the test. Add a new assert to test the new behaviour first.

newsfragments/772.bugfix

@@ -0,0 +1 @@
+Do not try to resolve file paths if they are not accessible.

src/dxtbx/serialize/filename.py

@@ -14,11 +14,15 @@ def resolve_path(path, directory=None):
       directory (Optional[str]): The local path to resolve relative links
 
     Returns:
-        str: The absolute path to the file to read
+        str: The absolute path to the file to read if accessible, otherwise
+        return the original path as provided
     """
     if not path:
         return ""
-    path = os.path.expanduser(os.path.expandvars(path))
-    if directory and not os.path.isabs(path):
-        path = os.path.join(directory, path)
-    return os.path.abspath(path)
+    trial_path = os.path.expanduser(os.path.expandvars(path))
+    if directory and not os.path.isabs(trial_path):
+        trial_path = os.path.join(directory, trial_path)
+    if os.path.exists(trial_path):
+        return os.path.abspath(trial_path)
+    else:
+        return path

tests/serialize/test_filename.py

@@ -1,15 +1,30 @@
 from __future__ import annotations
 
 import os
+import uuid
 
 from dxtbx.serialize.filename import resolve_path
 
 
 def test_resolve_path(monkeypatch):
+    # Resolve path
+    def alwaystrue(path):
+        return True
+
+    # Set an environment variable
     monkeypatch.setenv("HELLO_WORLD", "EXPANDED")
-    new_path = os.path.join("~", "$HELLO_WORLD", "path")
+
+    # First try a path that does not exist
+    filename = str(uuid.uuid4())
+    new_path = os.path.join("~", "$HELLO_WORLD", filename)
     path = resolve_path(new_path)
-    assert path == os.path.join(os.path.expanduser("~"), "EXPANDED", "path")
-    new_path = os.path.join("$HELLO_WORLD", "path")
+    assert path == new_path
+
+    # Now pretend the path exists
+    monkeypatch.setattr(os.path, "exists", alwaystrue)
+    path = resolve_path(new_path)
+    assert path == os.path.join(os.path.expanduser("~"), "EXPANDED", filename)
+
+    new_path = os.path.join("$HELLO_WORLD", filename)
     path = resolve_path(new_path)
-    assert path == os.path.abspath(os.path.join("EXPANDED", "path"))
+    assert path == os.path.abspath(os.path.join("EXPANDED", filename))