Add test cases for AST serialization (#3276)

The test cases use a serialized module in incremental mode
in various ways to make sure that all important information
in the AST nodes is preserved during serialization and
deserialization.

These are all very straightforward. The idea is to help catch
regressions early and to make it easier to refactor or optimize
serialization code. These found 2 issues -- separated the first
to PR #3275. The second issue (#3274) is still unfixed and there
is a skipped test case for it.

More complex cases such as import cycles can still go to
check-incremental.test.

Author: JukkaL

mypy/test/testcheck.py

@@ -55,6 +55,7 @@
     'check-semanal-error.test',
     'check-flags.test',
     'check-incremental.test',
+    'check-serialize.test',
     'check-bound.test',
     'check-optional.test',
     'check-fastparse.test',
@@ -90,27 +91,26 @@ def cases(cls) -> List[DataDrivenTestCase]:
         return c
 
     def run_case(self, testcase: DataDrivenTestCase) -> None:
-        incremental = 'incremental' in testcase.name.lower() or 'incremental' in testcase.file
+        incremental = ('incremental' in testcase.name.lower()
+                       or 'incremental' in testcase.file
+                       or 'serialize' in testcase.file)
         optional = 'optional' in testcase.file
-        if incremental:
-            # Incremental tests are run once with a cold cache, once with a warm cache.
-            # Expect success on first run, errors from testcase.output (if any) on second run.
-            # We briefly sleep to make sure file timestamps are distinct.
-            self.clear_cache()
-            self.run_case_once(testcase, 1)
-            self.run_case_once(testcase, 2)
-        elif optional:
-            try:
+        old_strict_optional = experiments.STRICT_OPTIONAL
+        try:
+            if incremental:
+                # Incremental tests are run once with a cold cache, once with a warm cache.
+                # Expect success on first run, errors from testcase.output (if any) on second run.
+                # We briefly sleep to make sure file timestamps are distinct.
+                self.clear_cache()
+                self.run_case_once(testcase, 1)
+                self.run_case_once(testcase, 2)
+            elif optional:
                 experiments.STRICT_OPTIONAL = True
                 self.run_case_once(testcase)
-            finally:
-                experiments.STRICT_OPTIONAL = False
-        else:
-            try:
-                old_strict_optional = experiments.STRICT_OPTIONAL
+            else:
                 self.run_case_once(testcase)
-            finally:
-                experiments.STRICT_OPTIONAL = old_strict_optional
+        finally:
+            experiments.STRICT_OPTIONAL = old_strict_optional
 
     def clear_cache(self) -> None:
         dn = defaults.CACHE_DIR

test-data/unit/check-incremental.test

@@ -26,6 +26,8 @@
 -- all cases so we can avoid constantly having to annotate it. The list of
 -- rechecked/stale files can be in any arbitrary order, or can be left empty
 -- if no files should be rechecked/stale.
+--
+-- There are additional incremental mode test cases in check-serialize.test.
 
 [case testIncrementalEmpty]
 [rechecked]
@@ -1711,28 +1713,6 @@ main:1: error: Module 'ntcrash' has no attribute 'nope'
 [out2]
 main:1: error: Module 'ntcrash' has no attribute 'nope'
 
-[case testIncrementalNamedTupleInMethod4]
-from ntcrash import C
-reveal_type(C().a)
-reveal_type(C().b)
-reveal_type(C().c)
-[file ntcrash.py]
-from typing import NamedTuple
-class C:
-    def __init__(self) -> None:
-        A = NamedTuple('A', [('x', int)])
-        self.a = A(0)
-        self.b = A(0)  # type: A
-        self.c = A
-[out1]
-main:2: error: Revealed type is 'Tuple[builtins.int, fallback=ntcrash.C.A@4]'
-main:3: error: Revealed type is 'Tuple[builtins.int, fallback=ntcrash.C.A@4]'
-main:4: error: Revealed type is 'def (x: builtins.int) -> Tuple[builtins.int, fallback=ntcrash.C.A@4]'
-[out2]
-main:2: error: Revealed type is 'Tuple[builtins.int, fallback=ntcrash.C.A@4]'
-main:3: error: Revealed type is 'Tuple[builtins.int, fallback=ntcrash.C.A@4]'
-main:4: error: Revealed type is 'def (x: builtins.int) -> Tuple[builtins.int, fallback=ntcrash.C.A@4]'
-
 [case testIncrementalTypedDictInMethod]
 from tdcrash import nope
 [file tdcrash.py]
@@ -1775,29 +1755,6 @@ main:1: error: Module 'tdcrash' has no attribute 'nope'
 [out2]
 main:1: error: Module 'tdcrash' has no attribute 'nope'
 
-[case testIncrementalTypedDictInMethod4]
-from ntcrash import C
-reveal_type(C().a)
-reveal_type(C().b)
-reveal_type(C().c)
-[file ntcrash.py]
-from mypy_extensions import TypedDict
-class C:
-    def __init__(self) -> None:
-        A = TypedDict('A', {'x': int})
-        self.a = A(x=0)
-        self.b = A(x=0)  # type: A
-        self.c = A
-[builtins fixtures/dict.pyi]
-[out1]
-main:2: error: Revealed type is 'TypedDict(x=builtins.int, _fallback=typing.Mapping[builtins.str, builtins.int])'
-main:3: error: Revealed type is 'TypedDict(x=builtins.int, _fallback=ntcrash.C.A@4)'
-main:4: error: Revealed type is 'def () -> ntcrash.C.A@4'
-[out2]
-main:2: error: Revealed type is 'TypedDict(x=builtins.int, _fallback=typing.Mapping[builtins.str, builtins.int])'
-main:3: error: Revealed type is 'TypedDict(x=builtins.int, _fallback=ntcrash.C.A@4)'
-main:4: error: Revealed type is 'def () -> ntcrash.C.A@4'
-
 [case testIncrementalInnerClassAttrInMethod]
 import crash
 nonexisting