Don't mark a module as stale if its children change (#8134)

This was introduced in #1865 to fix an issue with new children modules
being added. I think we have fixed this issue in another way also
since then, since the important part of the test passes with the check
removed. (I added some more stuff to the test to increase my
confidence in this change).

I want to remove this check because it causes a *ton* of trouble with
our internal bazel integrations, where we try to generate cache
artifacts for each bazel target separately. This check means that
bazel targets for packages have their caches invalidated all the time,
since they were generated without the children.

mypy/build.py

@@ -280,7 +280,6 @@ def normpath(path: str, options: Options) -> str:
                         ('data_mtime', int),  # mtime of data_json
                         ('data_json', str),  # path of <id>.data.json
                         ('suppressed', List[str]),  # dependencies that weren't imported
-                        ('child_modules', List[str]),  # all submodules of the given module
                         ('options', Optional[Dict[str, object]]),  # build options
                         # dep_prios and dep_lines are in parallel with
                         # dependencies + suppressed.
@@ -317,7 +316,6 @@ def cache_meta_from_dict(meta: Dict[str, Any], data_json: str) -> CacheMeta:
         int(meta['data_mtime']) if 'data_mtime' in meta else sentinel,
         data_json,
         meta.get('suppressed', []),
-        meta.get('child_modules', []),
         meta.get('options'),
         meta.get('dep_prios', []),
         meta.get('dep_lines', []),
@@ -1320,7 +1318,6 @@ def validate_meta(meta: Optional[CacheMeta], id: str, path: Optional[str],
                 'data_mtime': meta.data_mtime,
                 'dependencies': meta.dependencies,
                 'suppressed': meta.suppressed,
-                'child_modules': meta.child_modules,
                 'options': (manager.options.clone_for_module(id)
                             .select_options_affecting_cache()),
                 'dep_prios': meta.dep_prios,
@@ -1364,7 +1361,7 @@ def json_dumps(obj: Any, debug_cache: bool) -> str:
 
 def write_cache(id: str, path: str, tree: MypyFile,
                 dependencies: List[str], suppressed: List[str],
-                child_modules: List[str], dep_prios: List[int], dep_lines: List[int],
+                dep_prios: List[int], dep_lines: List[int],
                 old_interface_hash: str, source_hash: str,
                 ignore_all: bool, manager: BuildManager) -> Tuple[str, Optional[CacheMeta]]:
     """Write cache files for a module.
@@ -1379,7 +1376,6 @@ def write_cache(id: str, path: str, tree: MypyFile,
       tree: the fully checked module data
       dependencies: module IDs on which this module depends
       suppressed: module IDs which were suppressed as dependencies
-      child_modules: module IDs which are this package's direct submodules
       dep_prios: priorities (parallel array to dependencies)
       dep_lines: import line locations (parallel array to dependencies)
       old_interface_hash: the hash from the previous version of the data cache file
@@ -1469,7 +1465,6 @@ def write_cache(id: str, path: str, tree: MypyFile,
             'data_mtime': data_mtime,
             'dependencies': dependencies,
             'suppressed': suppressed,
-            'child_modules': child_modules,
             'options': options.select_options_affecting_cache(),
             'dep_prios': dep_prios,
             'dep_lines': dep_lines,
@@ -1688,9 +1683,6 @@ class State:
     # Parent package, its parent, etc.
     ancestors = None  # type: Optional[List[str]]
 
-    # A list of all direct submodules of a given module
-    child_modules = None  # type: Set[str]
-
     # List of (path, line number) tuples giving context for import
     import_context = None  # type: List[Tuple[str, int]]
 
@@ -1797,7 +1789,6 @@ def __init__(self,
             assert len(all_deps) == len(self.meta.dep_lines)
             self.dep_line_map = {id: line
                                  for id, line in zip(all_deps, self.meta.dep_lines)}
-            self.child_modules = set(self.meta.child_modules)
             if temporary:
                 self.load_tree(temporary=True)
             if not manager.use_fine_grained_cache():
@@ -1824,7 +1815,6 @@ def __init__(self,
             # Parse the file (and then some) to get the dependencies.
             self.parse_file()
             self.compute_dependencies()
-            self.child_modules = set()
 
     @property
     def xmeta(self) -> CacheMeta:
@@ -1855,8 +1845,7 @@ def is_fresh(self) -> bool:
         # dependency is added back we find out later in the process.
         return (self.meta is not None
                 and self.is_interface_fresh()
-                and self.dependencies == self.meta.dependencies
-                and self.child_modules == set(self.meta.child_modules))
+                and self.dependencies == self.meta.dependencies)
 
     def is_interface_fresh(self) -> bool:
         return self.externally_same
@@ -2241,7 +2230,7 @@ def write_cache(self) -> None:
             "Duplicates in dependencies list for {} ({})".format(self.id, self.dependencies))
         new_interface_hash, self.meta = write_cache(
             self.id, self.path, self.tree,
-            list(self.dependencies), list(self.suppressed), list(self.child_modules),
+            list(self.dependencies), list(self.suppressed),
             dep_prios, dep_lines, self.interface_hash, self.source_hash, self.ignore_all,
             self.manager)
         if new_interface_hash == self.interface_hash:
@@ -2795,8 +2784,6 @@ def load_graph(sources: List[BuildSource], manager: BuildManager,
                     assert newst.id not in graph, newst.id
                     graph[newst.id] = newst
                     new.append(newst)
-            if dep in st.ancestors and dep in graph:
-                graph[dep].child_modules.add(st.id)
             if dep in graph and dep in st.suppressed_set:
                 # Previously suppressed file is now visible
                 st.add_dependency(dep)

test-data/unit/check-incremental.test

@@ -947,11 +947,15 @@ from parent import a
 
 [file parent/a.py.2]
 from parent import b
+reveal_type(b.x)
 
 [file parent/b.py.2]
+x = 10
 
-[stale parent.a, parent.b]
-[rechecked parent, parent.a, parent.b]
+[stale parent.b]
+[rechecked parent.a, parent.b]
+[out2]
+tmp/parent/a.py:2: note: Revealed type is 'builtins.int'
 
 [case testIncrementalReferenceExistingFileWithImportFrom]
 from parent import a, b