Ensure errors persist after dmypy update

Before this change, if a module was removed with `update` in the
`FineGrainedBuildManager`, then some errors would not re-appear.

This change ensures that three types of error are maintained when
running `reprocess_nodes`:

- possibly undefined vars
- unused ignores
- ignores without codes

By adding targets to ErrorInfos, this also fixes an issue where unused
ignore and ignores without codes errors didn't get re-processed when
they were the only issue in the file.

Fixes python#9655

mypy/errors.py

@@ -668,6 +668,8 @@ def generate_unused_ignore_errors(self, file: str) -> None:
                 False,
                 False,
                 False,
+                origin=(self.file, None),
+                target=self.target_module,
             )
             self._add_error_info(file, info)
 
@@ -720,6 +722,8 @@ def generate_ignore_without_code_errors(
                 False,
                 False,
                 False,
+                origin=(self.file, None),
+                target=self.target_module,
             )
             self._add_error_info(file, info)
 

mypy/server/update.py

@@ -1027,6 +1027,10 @@ def key(node: FineGrainedDeferredNode) -> int:
         if graph[module_id].type_checker().check_second_pass():
             more = True
 
+    graph[module_id].detect_possibly_undefined_vars()
+    graph[module_id].generate_unused_ignore_notes()
+    graph[module_id].generate_ignore_without_code_notes()
+
     if manager.options.export_types:
         manager.all_types.update(graph[module_id].type_map())