Fix caching behavior of PEP561-installed namespace packages

Since PEP561-installed namespace packages only show up in
FindModuleCache as a side-effect, the submodules need to be listed
first in the dependencies for things to work. This was handled already
in the Import case but not the ImportFrom case.

Also fix the cache handling of namespace packages so it doesn't always
get reported stale.

Fixes #9852.

mypy/build.py

@@ -751,7 +751,6 @@ def correct_rel_imp(imp: Union[ImportFrom, ImportAll]) -> str:
                             res.append((ancestor_pri, ".".join(ancestors), imp.line))
                 elif isinstance(imp, ImportFrom):
                     cur_id = correct_rel_imp(imp)
-                    pos = len(res)
                     all_are_submodules = True
                     # Also add any imported names that are submodules.
                     pri = import_priority(imp, PRI_MED)
@@ -768,7 +767,10 @@ def correct_rel_imp(imp: Union[ImportFrom, ImportAll]) -> str:
                     # if all of the imports are submodules, do the import at a lower
                     # priority.
                     pri = import_priority(imp, PRI_HIGH if not all_are_submodules else PRI_LOW)
-                    res.insert(pos, ((pri, cur_id, imp.line)))
+                    # The imported module goes in after the
+                    # submodules, for the same namespace related
+                    # reasons discussed in the Import case.
+                    res.append((pri, cur_id, imp.line))
                 elif isinstance(imp, ImportAll):
                     pri = import_priority(imp, PRI_HIGH)
                     res.append((pri, correct_rel_imp(imp), imp.line))
@@ -1317,7 +1319,7 @@ def validate_meta(meta: Optional[CacheMeta], id: str, path: Optional[str],
         st = manager.get_stat(path)
     except OSError:
         return None
-    if not stat.S_ISREG(st.st_mode):
+    if not (stat.S_ISREG(st.st_mode) or stat.S_ISDIR(st.st_mode)):
         manager.log('Metadata abandoned for {}: file {} does not exist'.format(id, path))
         return None
 
@@ -1360,7 +1362,11 @@ def validate_meta(meta: Optional[CacheMeta], id: str, path: Optional[str],
 
         t0 = time.time()
         try:
-            source_hash = manager.fscache.hash_digest(path)
+            # dir means it is a namespace package
+            if stat.S_ISDIR(st.st_mode):
+                source_hash = ''
+            else:
+                source_hash = manager.fscache.hash_digest(path)
         except (OSError, UnicodeDecodeError, DecodeError):
             return None
         manager.add_stats(validate_hash_time=time.time() - t0)
@@ -1838,7 +1844,7 @@ def __init__(self,
         if path and source is None and self.manager.fscache.isdir(path):
             source = ''
         self.source = source
-        if path and source is None and self.manager.cache_enabled:
+        if path and self.manager.cache_enabled:
             self.meta = find_cache_meta(self.id, path, manager)
             # TODO: Get mtime if not cached.
             if self.meta is not None:
@@ -2038,6 +2044,9 @@ def parse_file(self) -> None:
                     else:
                         err = "mypy: can't decode file '{}': {}".format(self.path, str(decodeerr))
                     raise CompileError([err], module_with_blocker=self.id) from decodeerr
+            elif self.path and self.manager.fscache.isdir(self.path):
+                source = ''
+                self.source_hash = ''
             else:
                 assert source is not None
                 self.source_hash = compute_hash(source)

test-data/unit/check-incremental.test

@@ -5563,3 +5563,25 @@ class D:
 [out2]
 tmp/a.py:2: note: Revealed type is "builtins.list[builtins.int]"
 tmp/a.py:3: note: Revealed type is "builtins.list[builtins.str]"
+
+[case testIncrementalNamespacePackage1]
+# flags: --namespace-packages
+import m
+[file m.py]
+from foo.bar import x
+x + 0
+[file foo/bar.py]
+x = 0
+[rechecked]
+[stale]
+
+[case testIncrementalNamespacePackage2]
+# flags: --namespace-packages
+import m
+[file m.py]
+from foo import bar
+bar.x + 0
+[file foo/bar.py]
+x = 0
+[rechecked]
+[stale]

test-data/unit/pep561.test

@@ -187,9 +187,8 @@ import a
 [out2]
 a.py:1: error: Unsupported operand types for + ("int" and "str")
 
--- Test for issue #9852, among others
-[case testTypedPkgNamespaceRegFromImportTwice-xfail]
-# pkgs: typedpkg, typedpkg_ns
+[case testTypedPkgNamespaceRegFromImportTwice]
+# pkgs: typedpkg_ns
 from typedpkg_ns import ns
 -- dummy should trigger a second iteration
 [file dummy.py.2]