Preserve (some) implicitly exported types (#13967)

Fixes some of #13965, fixes #12749

We also need to modify attribute access logic (this is the TODO in the
PR), which is a little trickier. But cases like #13933 convinced me it's
worth making this change, even before I get around to figuring that out.

Author: hauntsaninja

mypy/semanal.py

@@ -2303,10 +2303,20 @@ def visit_import_from(self, imp: ImportFrom) -> None:
                     )
                     continue
 
-            if node and not node.module_hidden:
+            if node:
                 self.process_imported_symbol(
                     node, module_id, id, imported_id, fullname, module_public, context=imp
                 )
+                if node.module_hidden:
+                    self.report_missing_module_attribute(
+                        module_id,
+                        id,
+                        imported_id,
+                        module_public=module_public,
+                        module_hidden=not module_public,
+                        context=imp,
+                        add_unknown_imported_symbol=False,
+                    )
             elif module and not missing_submodule:
                 # Target module exists but the imported name is missing or hidden.
                 self.report_missing_module_attribute(
@@ -2394,6 +2404,7 @@ def report_missing_module_attribute(
         module_public: bool,
         module_hidden: bool,
         context: Node,
+        add_unknown_imported_symbol: bool = True,
     ) -> None:
         # Missing attribute.
         if self.is_incomplete_namespace(import_id):
@@ -2418,13 +2429,14 @@ def report_missing_module_attribute(
                     suggestion = f"; maybe {pretty_seq(matches, 'or')}?"
                     message += f"{suggestion}"
         self.fail(message, context, code=codes.ATTR_DEFINED)
-        self.add_unknown_imported_symbol(
-            imported_id,
-            context,
-            target_name=None,
-            module_public=module_public,
-            module_hidden=not module_public,
-        )
+        if add_unknown_imported_symbol:
+            self.add_unknown_imported_symbol(
+                imported_id,
+                context,
+                target_name=None,
+                module_public=module_public,
+                module_hidden=not module_public,
+            )
 
         if import_id == "typing":
             # The user probably has a missing definition in a test fixture. Let's verify.

test-data/unit/check-flags.test

@@ -1606,14 +1606,19 @@ strict_equality = false
 
 
 [case testNoImplicitReexport]
-# flags: --no-implicit-reexport
-from other_module_2 import a
+# flags: --no-implicit-reexport --show-error-codes
+from other_module_2 import a  # E: Module "other_module_2" does not explicitly export attribute "a"  [attr-defined]
+reveal_type(a)  # N: Revealed type is "builtins.int"
+
+import other_module_2
+# TODO: this should also reveal builtins.int, see #13965
+reveal_type(other_module_2.a)  # E: "object" does not explicitly export attribute "a"  [attr-defined] \
+                               # N: Revealed type is "Any"
+
 [file other_module_1.py]
 a = 5
 [file other_module_2.py]
 from other_module_1 import a
-[out]
-main:2: error: Module "other_module_2" does not explicitly export attribute "a"
 
 [case testNoImplicitReexportRespectsAll]
 # flags: --no-implicit-reexport

test-data/unit/check-modules.test

@@ -1794,7 +1794,7 @@ from stub import C
 c = C()
 reveal_type(c.x)  # N: Revealed type is "builtins.int"
 it: Iterable[int]
-reveal_type(it)  # N: Revealed type is "Any"
+reveal_type(it)  # N: Revealed type is "typing.Iterable[builtins.int]"
 
 [file stub.pyi]
 from typing import Iterable