More improvements to following imports in mypy daemon (#8616)

This includes a bunch of changes to following imports:

* Fix bug with cached modules without ASTs by loading the AST as needed
* Improve docstrings and simplify code
* Rename `follow_imports`
* Merge `seen` and `sources_set`
* Address some TODO items

This may be easier to review by looking at individual commits.

I think that following imports is ready to be enabled after this has been
merged. We can always revert the change before the next release if we
we encounter major issues.

Major things I know about that still don't work (I'll try to address at least the 
first one before the next release):

* `-m` and `-p` don't work correctly with dmypy (I think that happens also
  in other modes, but might be worse when following imports)
* Suppressed modules are incorrect with namespace modules (happens
  also in other modes)
* File events are not supported (but these are undocumented, so it's
  not critical?)
* Performance with a huge number of files is unknown (other import modes
  have better performance and can be used as fallbacks if this is a problem)

Work towards #5870.

Continues progress made in #8590.

mypy/dmypy_server.py

@@ -534,25 +534,23 @@ def fine_grained_increment_follow_imports(self, sources: List[BuildSource]) -> L
 
         orig_modules = list(graph.keys())
 
-        # TODO: Are the differences from fine_grained_increment(), necessary?
         self.update_sources(sources)
         changed_paths = self.fswatcher.find_changed()
         manager.search_paths = compute_search_paths(sources, manager.options, manager.data_dir)
 
         t1 = time.time()
         manager.log("fine-grained increment: find_changed: {:.3f}s".format(t1 - t0))
 
-        sources_set = {source.module for source in sources}
+        seen = {source.module for source in sources}
 
         # Find changed modules reachable from roots (or in roots) already in graph.
-        seen = set()  # type: Set[str]
-        changed, removed, new_files = self.follow_imports(
-            sources, graph, seen, changed_paths, sources_set
+        changed, new_files = self.find_reachable_changed_modules(
+            sources, graph, seen, changed_paths
         )
         sources.extend(new_files)
 
         # Process changes directly reachable from roots.
-        messages = fine_grained_manager.update(changed, removed)
+        messages = fine_grained_manager.update(changed, [])
 
         # Follow deps from changed modules (still within graph).
         worklist = changed[:]
@@ -561,31 +559,31 @@ def fine_grained_increment_follow_imports(self, sources: List[BuildSource]) -> L
             if module[0] not in graph:
                 continue
             sources2 = self.direct_imports(module, graph)
-            changed, removed, new_files = self.follow_imports(
-                sources2, graph, seen, changed_paths, sources_set
+            changed, new_files = self.find_reachable_changed_modules(
+                sources2, graph, seen, changed_paths
             )
-            sources.extend(new_files)
             self.update_sources(new_files)
-            messages = fine_grained_manager.update(changed, removed)
-            # TODO: Removed?
+            messages = fine_grained_manager.update(changed, [])
             worklist.extend(changed)
 
         t2 = time.time()
 
-        for module_id, state in graph.items():
-            refresh_suppressed_submodules(module_id, state.path, fine_grained_manager.deps, graph,
-                                          self.fscache)
+        def refresh_file(module: str, path: str) -> List[str]:
+            return fine_grained_manager.update([(module, path)], [])
+
+        for module_id, state in list(graph.items()):
+            new_messages = refresh_suppressed_submodules(
+                module_id, state.path, fine_grained_manager.deps, graph, self.fscache, refresh_file
+            )
+            if new_messages is not None:
+                messages = new_messages
 
         t3 = time.time()
 
         # There may be new files that became available, currently treated as
         # suppressed imports. Process them.
-        seen_suppressed = set()  # type: Set[str]
         while True:
-            # TODO: Merge seen and seen_suppressed?
-            new_unsuppressed, seen_suppressed = self.find_added_suppressed(
-                graph, seen_suppressed, manager.search_paths
-            )
+            new_unsuppressed = self.find_added_suppressed(graph, seen, manager.search_paths)
             if not new_unsuppressed:
                 break
             new_files = [BuildSource(mod[1], mod[0]) for mod in new_unsuppressed]
@@ -594,8 +592,15 @@ def fine_grained_increment_follow_imports(self, sources: List[BuildSource]) -> L
             messages = fine_grained_manager.update(new_unsuppressed, [])
 
             for module_id, path in new_unsuppressed:
-                refresh_suppressed_submodules(module_id, path, fine_grained_manager.deps, graph,
-                                              self.fscache)
+                new_messages = refresh_suppressed_submodules(
+                    module_id, path,
+                    fine_grained_manager.deps,
+                    graph,
+                    self.fscache,
+                    refresh_file
+                )
+                if new_messages is not None:
+                    messages = new_messages
 
         t4 = time.time()
 
@@ -604,7 +609,7 @@ def fine_grained_increment_follow_imports(self, sources: List[BuildSource]) -> L
         for module_id in orig_modules:
             if module_id not in graph:
                 continue
-            if module_id not in seen and module_id not in seen_suppressed:
+            if module_id not in seen:
                 module_path = graph[module_id].path
                 assert module_path is not None
                 to_delete.append((module_id, module_path))
@@ -631,33 +636,35 @@ def fine_grained_increment_follow_imports(self, sources: List[BuildSource]) -> L
 
         return messages
 
-    def follow_imports(self,
-                       sources: List[BuildSource],
-                       graph: mypy.build.Graph,
-                       seen: Set[str],
-                       changed_paths: AbstractSet[str],
-                       sources_set: Set[str]) -> Tuple[List[Tuple[str, str]],
-                                                       List[Tuple[str, str]],
-                                                       List[BuildSource]]:
-        """Follow imports within graph from given sources.
+    def find_reachable_changed_modules(
+            self,
+            roots: List[BuildSource],
+            graph: mypy.build.Graph,
+            seen: Set[str],
+            changed_paths: AbstractSet[str]) -> Tuple[List[Tuple[str, str]],
+                                                      List[BuildSource]]:
+        """Follow imports within graph from given sources until hitting changed modules.
+
+        If we find a changed module, we can't continue following imports as the imports
+        may have changed.
 
         Args:
-            sources: roots of modules to search
+            roots: modules where to start search from
             graph: module graph to use for the search
-            seen: modules we've seen before that won't be visited (mutated here!)
+            seen: modules we've seen before that won't be visited (mutated here!!)
             changed_paths: which paths have changed (stop search here and return any found)
-            sources_set: set of sources (TODO: relationship with seen)
 
-        Return (reachable changed modules, removed modules, updated file list).
+        Return (encountered reachable changed modules,
+                unchanged files not in sources_set traversed).
         """
         changed = []
         new_files = []
-        worklist = sources[:]
+        worklist = roots[:]
         seen.update(source.module for source in worklist)
         while worklist:
             nxt = worklist.pop()
-            if nxt.module not in sources_set:
-                sources_set.add(nxt.module)
+            if nxt.module not in seen:
+                seen.add(nxt.module)
                 new_files.append(nxt)
             if nxt.path in changed_paths:
                 assert nxt.path is not None  # TODO
@@ -669,7 +676,7 @@ def follow_imports(self,
                         seen.add(dep)
                         worklist.append(BuildSource(graph[dep].path,
                                                     graph[dep].id))
-        return changed, [], new_files
+        return changed, new_files
 
     def direct_imports(self,
                        module: Tuple[str, str],
@@ -682,8 +689,14 @@ def direct_imports(self,
     def find_added_suppressed(self,
                               graph: mypy.build.Graph,
                               seen: Set[str],
-                              search_paths: SearchPaths) -> Tuple[List[Tuple[str, str]], Set[str]]:
-        """Find suppressed modules that have been added (and not included in seen)."""
+                              search_paths: SearchPaths) -> List[Tuple[str, str]]:
+        """Find suppressed modules that have been added (and not included in seen).
+
+        Args:
+            seen: reachable modules we've seen before (mutated here!!)
+
+        Return suppressed, added modules.
+        """
         all_suppressed = set()
         for module, state in graph.items():
             all_suppressed |= state.suppressed_set
@@ -693,7 +706,6 @@ def find_added_suppressed(self,
         all_suppressed = {module for module in all_suppressed if module not in graph}
 
         # TODO: Namespace packages
-        # TODO: Handle seen?
 
         finder = FindModuleCache(search_paths, self.fscache, self.options)
 
@@ -705,7 +717,7 @@ def find_added_suppressed(self,
                 found.append((module, result))
                 seen.add(module)
 
-        return found, seen
+        return found
 
     def increment_output(self,
                          messages: List[str],

mypy/server/update.py

@@ -116,7 +116,7 @@
 import sys
 import time
 from typing import (
-    Dict, List, Set, Tuple, Union, Optional, NamedTuple, Sequence
+    Dict, List, Set, Tuple, Union, Optional, NamedTuple, Sequence, Callable
 )
 from typing_extensions import Final
 
@@ -1127,7 +1127,8 @@ def refresh_suppressed_submodules(
         path: Optional[str],
         deps: Dict[str, Set[str]],
         graph: Graph,
-        fscache: FileSystemCache) -> None:
+        fscache: FileSystemCache,
+        refresh_file: Callable[[str, str], List[str]]) -> Optional[List[str]]:
     """Look for submodules that are now suppressed in target package.
 
     If a submodule a.b gets added, we need to mark it as suppressed
@@ -1139,10 +1140,15 @@ def refresh_suppressed_submodules(
     Args:
         module: target package in which to look for submodules
         path: path of the module
+        refresh_file: function that reads the AST of a module (returns error messages)
+
+    Return a list of errors from refresh_file() if it was called. If the
+    return value is None, we didn't call refresh_file().
     """
+    messages = None
     if path is None or not path.endswith(INIT_SUFFIXES):
         # Only packages have submodules.
-        return
+        return None
     # Find any submodules present in the directory.
     pkgdir = os.path.dirname(path)
     for fnam in fscache.listdir(pkgdir):
@@ -1153,22 +1159,33 @@ def refresh_suppressed_submodules(
         shortname = fnam.split('.')[0]
         submodule = module + '.' + shortname
         trigger = make_trigger(submodule)
+
+        # We may be missing the required fine-grained deps.
+        ensure_deps_loaded(module, deps, graph)
+
         if trigger in deps:
             for dep in deps[trigger]:
-                # TODO: <...> deps, etc.
+                # We can ignore <...> deps since a submodule can't trigger any.
                 state = graph.get(dep)
                 if not state:
                     # Maybe it's a non-top-level target. We only care about the module.
                     dep_module = module_prefix(graph, dep)
                     if dep_module is not None:
                         state = graph.get(dep_module)
                 if state:
+                    # Is the file may missing an AST in case it's read from cache?
+                    if state.tree is None:
+                        # Create AST for the file. This may produce some new errors
+                        # that we need to propagate.
+                        assert state.path is not None
+                        messages = refresh_file(state.id, state.path)
                     tree = state.tree
-                    assert tree  # TODO: What if doesn't exist?
+                    assert tree  # Will be fine, due to refresh_file() above
                     for imp in tree.imports:
                         if isinstance(imp, ImportFrom):
                             if (imp.id == module
-                                    and any(name == shortname for name, _ in imp.names)):
-                                # TODO: Only if does not exist already
+                                    and any(name == shortname for name, _ in imp.names)
+                                    and submodule not in state.suppressed_set):
                                 state.suppressed.append(submodule)
                                 state.suppressed_set.add(submodule)
+    return messages

test-data/unit/fine-grained-follow-imports.test

@@ -700,3 +700,22 @@ import bar
 ==
 src/foo.py:2: error: "str" not callable
 src/bar.py:1: error: "int" not callable
+
+[case testFollowImportsNormalSuppressedAffectsCachedFile-only_when_cache]
+# flags: --follow-imports=normal
+# cmd: mypy main.py
+
+[file main.py]
+from p import m  # type: ignore
+m.f(1)
+
+[file p/__init__.py]
+
+[file p/m.py.2]
+# This change will trigger a cached file (main.py) through a supressed
+# submodule, resulting in additional errors in main.py.
+def f() -> None: pass
+
+[out]
+==
+main.py:2: error: Too many arguments for "f"