More robust fix for re-export of __all__ (#20487)

This allows to re-enable one test skipped in parallel mode.

The previous solution for re-export of `__all__` (see
#10382) didn't work on incremental
runs (see added test).

Author: ilevkivskyi

mypy/semanal.py

@@ -494,6 +494,8 @@ def __init__(
         self.incomplete_namespaces = incomplete_namespaces
         self.all_exports: list[str] = []
         # Map from module id to list of explicitly exported names (i.e. names in __all__).
+        # This is used by stubgen/stubtest, DO NOT use for any other purposes as it is
+        # not populated on incremental runs (nor in parallel mode).
         self.export_map: dict[str, list[str]] = {}
         self.plugin = plugin
         # If True, process function definitions. If False, don't. This is used
@@ -2967,8 +2969,13 @@ def visit_import_from(self, imp: ImportFrom) -> None:
                 # precedence, but doesn't seem to be important in most use cases.
                 node = SymbolTableNode(GDEF, self.modules[fullname])
             else:
-                if id == as_id == "__all__" and module_id in self.export_map:
-                    self.all_exports[:] = self.export_map[module_id]
+                if id == as_id == "__all__":
+                    # For modules with __all__ public status of symbols is determined uniquely
+                    # by contents of __all__, so we can recover the latter here, and avoid
+                    # serializing this (redundant) information in MypyFile.
+                    self.all_exports[:] = [
+                        name for name, sym in module.names.items() if sym.module_public
+                    ]
                 node = module.names.get(id)
 
             missing_submodule = False

test-data/unit/check-incremental.test

@@ -7635,3 +7635,32 @@ def wrong() -> int:
 main:2: error: Missing return statement
 [out2]
 {"file": "main", "line": 2, "column": 0, "message": "Missing return statement", "hint": null, "code": "return", "severity": "error"}
+
+[case testReExportAllInStubIncremental]
+from m1 import C
+from m1 import D
+C()
+C(1)
+[file m1.pyi]
+from m2 import *
+[file m2.pyi]
+from m3 import *
+from m3 import __all__ as __all__
+class D: pass
+[file m2.pyi.2]
+from m3 import *
+from m3 import __all__ as __all__
+class D:
+    x = 1
+[file m3.pyi]
+from m4 import C as C
+__all__ = ['C']
+[file m4.pyi]
+class C: pass
+[builtins fixtures/list.pyi]
+[out]
+main:2: error: Module "m1" has no attribute "D"
+main:4: error: Too many arguments for "C"
+[out2]
+main:2: error: Module "m1" has no attribute "D"
+main:4: error: Too many arguments for "C"

test-data/unit/check-modules.test

@@ -2960,7 +2960,7 @@ class Some:
     name = __name__
 reveal_type(Some.name)  # N: Revealed type is "builtins.str"
 
-[case testReExportAllInStub_no_parallel]
+[case testReExportAllInStub]
 from m1 import C
 from m1 import D  # E: Module "m1" has no attribute "D"
 C()