Fix using network shares for extensions on WIN32

- Support UNC paths.
- Normalize URL's to account for differences between browsers.

scripts/addons_core/bl_pkg/bl_extension_ops.py

@@ -70,6 +70,26 @@ def url_append_defaults(url):
     return url_append_query_for_blender(url, blender_version=bpy.app.version)
 
 
+def url_normalize(url):
+    # Ensure consistent use of `file://` so multiple representations aren't considered different repositories.
+    # Currently this only makes changes for UNC paths on WIN32.
+    import sys
+    import re
+
+    prefix = "file://"
+    if url.startswith(prefix):
+        if sys.platform == "win32":
+            # Not a drive, e.g. `file:///C:/path`.
+            path_lstrip = url[len(prefix):].lstrip("/")
+            if re.match("[A-Za-z]:", path_lstrip) is None:
+                # Ensure:
+                # MS-Edge uses: `file://HOST/share/path`
+                # Firefox uses: `file://///HOST/share/path`
+                # Both can work prefer the shorter one.
+                url = prefix + path_lstrip
+    return url
+
+
 def rna_prop_repo_enum_valid_only_itemf(_self, context):
     if context is None:
         result = []
@@ -2589,6 +2609,9 @@ class EXTENSIONS_OT_package_install(Operator, _ExtCmdMixIn):
         url = self.url
         print("DROP URL:", url)
 
+        # Needed for UNC paths on WIN32.
+        url = self.url = url_normalize(url)
+
         url, url_params = url_parse_for_blender(url)
 
         # Check if the extension is compatible with the current platform.

scripts/addons_core/bl_pkg/cli/blender_ext.py

@@ -373,9 +373,20 @@ def path_from_url(path: str) -> str:
     if sys.platform == "win32":
         # MS-Windows needs special handling for drive letters.
         # `file:///C:/test` is converted to `/C:/test` which must skip the leading slash.
-        if re.match("/[A-Za-z]:", path_unquote):
-            path_unquote = path_unquote[1:]
-    return os.path.join(p.netloc, path_unquote)
+        if (p.netloc == "") and re.match("/[A-Za-z]:", path_unquote):
+            result = path_unquote[1:]
+        else:
+            # Handle UNC paths: `\\HOST\share\path` as a URL on MS-Windows.
+            # - MS-Edge: `file://HOST/share/path` where `netloc="HOST"`, `path="/share/path"`.
+            # - Firefox: `file://///HOST/share/path`  where `netloc=""`, `path="///share/path"`.
+            if p.netloc:
+                result = "//{:s}/{:s}".format(p.netloc, path_unquote.lstrip("/"))
+            else:
+                result = "//{:s}".format(path_unquote.lstrip("/"))
+    else:
+        result = os.path.join(p.netloc, path_unquote)
+
+    return result
 
 
 def random_acii_lines(*, seed: Union[int, str], width: int) -> Generator[str, None, None]: