Change relative path handling:

* Assign relativePath using PathUtils.get_relative_path, which returns None
    if no relative path exists (e.g. different drive);
    this aligns with how it was originally handled in multilspy
  * Adapt all places where we can now enounter None instead of a string

src/multilspy/language_server.py

@@ -525,13 +525,7 @@ class LanguageServer:
                     new_item: multilspy_types.Location = {}
                     new_item.update(item)
                     new_item["absolutePath"] = PathUtils.uri_to_path(new_item["uri"])
-                    try:
-                        # TODO can we use PathUtils.get_relative_path? (same elsewhere!)
-                        new_item["relativePath"] = str(
-                            PurePath(os.path.relpath(new_item["absolutePath"], self.repository_root_path))
-                        )
-                    except:
-                        new_item["relativePath"] = str(new_item["absolutePath"])
+                    new_item["relativePath"] = PathUtils.get_relative_path(new_item["absolutePath"], self.repository_root_path)
                     ret.append(multilspy_types.Location(new_item))
                 elif (
                     LSPConstants.ORIGIN_SELECTION_RANGE in item
@@ -542,12 +536,7 @@ class LanguageServer:
                     new_item: multilspy_types.Location = {}
                     new_item["uri"] = item[LSPConstants.TARGET_URI]
                     new_item["absolutePath"] = PathUtils.uri_to_path(new_item["uri"])
-                    try:
-                        new_item["relativePath"] = str(
-                            PurePath(os.path.relpath(new_item["absolutePath"], self.repository_root_path))
-                        )
-                    except:
-                        new_item["relativePath"] = str(new_item["absolutePath"])
+                    new_item["relativePath"] = PathUtils.get_relative_path(new_item["absolutePath"], self.repository_root_path)
                     new_item["range"] = item[LSPConstants.TARGET_SELECTION_RANGE]
                     ret.append(multilspy_types.Location(**new_item))
                 else:
@@ -943,6 +932,7 @@ class LanguageServer:
                 elif os.path.isfile(abs_item_path):
                     _, root_nodes = await self.request_document_symbols(item_path, include_body=include_body)
 
+                    # TODO: Not sure if this is actually still needed given recent changes to relative path handling
                     def fix_relative_path(nodes: List[multilspy_types.UnifiedSymbolInformation]):
                         for node in nodes:
                             path = Path(node["location"]["relativePath"])

src/serena/symbol.py

@@ -23,9 +23,9 @@ class SymbolLocation:
     Represents the (start) location of a symbol identifier
     """
 
-    relative_path: str
+    relative_path: str | None
     """
-    the relative path of the file containing the symbol
+    the relative path of the file containing the symbol; if None, the symbol is defined outside of the project's scope
     """
     line: int | None
     """
@@ -39,13 +39,14 @@ class SymbolLocation:
     """
 
     def __post_init__(self) -> None:
-        self.relative_path = self.relative_path.replace("/", os.path.sep)
+        if self.relative_path is not None:
+            self.relative_path = self.relative_path.replace("/", os.path.sep)
 
     def to_dict(self) -> dict[str, Any]:
         return asdict(self)
 
     def has_position_in_file(self) -> bool:
-        return self.line is not None and self.column is not None
+        return self.relative_path is not None and self.line is not None and self.column is not None
 
 
 class Symbol(ToStringMixin):
@@ -71,7 +72,7 @@ class Symbol(ToStringMixin):
         return self.s["kind"]
 
     @property
-    def relative_path(self) -> str:
+    def relative_path(self) -> str | None:
         return self.s["location"]["relativePath"]
 
     @property
@@ -239,6 +240,8 @@ class SymbolManager:
         return symbols
 
     def find_by_location(self, location: SymbolLocation) -> Symbol | None:
+        if location.relative_path is None:
+            return None
         symbol_dicts, roots = self.lang_server.request_document_symbols(location.relative_path, include_body=False)
         for symbol_dict in symbol_dicts:
             symbol = Symbol(symbol_dict)
@@ -268,6 +271,7 @@ class SymbolManager:
         """
         if not symbol_location.has_position_in_file():
             raise ValueError("Symbol location does not contain a valid position in a file")
+        assert symbol_location.relative_path is not None
         assert symbol_location.line is not None
         assert symbol_location.column is not None
         symbol_dicts = self.lang_server.request_referencing_symbols(
@@ -301,7 +305,8 @@ class SymbolManager:
     def _edited_symbol_location(self, location: SymbolLocation) -> Iterator[Symbol]:
         symbol = self.find_by_location(location)
         if symbol is None:
-            raise ValueError("Symbol not found")
+            raise ValueError("Symbol not found/has no defined location within a file")
+        assert location.relative_path is not None
         with self._edited_file(location.relative_path):
             yield symbol
 
@@ -313,6 +318,7 @@ class SymbolManager:
         :param body: the new body
         """
         with self._edited_symbol_location(location) as symbol:
+            assert location.relative_path is not None
             self.lang_server.delete_text_between_positions(location.relative_path, symbol.body_start_position, symbol.body_end_position)
             self.lang_server.insert_text_at_position(
                 location.relative_path, symbol.body_start_position["line"], symbol.body_start_position["character"], body
@@ -327,6 +333,7 @@ class SymbolManager:
         """
         with self._edited_symbol_location(location) as symbol:
             pos = symbol.body_end_position
+            assert location.relative_path is not None
             self.lang_server.insert_text_at_position(location.relative_path, pos["line"], pos["character"], body)
 
     def insert_before(self, location: SymbolLocation, body: str) -> None:
@@ -338,6 +345,7 @@ class SymbolManager:
         """
         with self._edited_symbol_location(location) as symbol:
             pos = copy(symbol.body_start_position)
+            assert location.relative_path is not None
             self.lang_server.insert_text_at_position(location.relative_path, pos["line"], pos["character"], body)
 
     def insert_at_line(self, relative_path: str, line: int, content: str) -> None: