Test interactions with silent imports and errors

This commit adds several more tests to try and check if mypy behaves
correctly under a variety silent import related scenarios, and if it
behaves correctly starting from an initial error.

Author: MichaelLeeDBX

test-data/unit/check-incremental.test

@@ -1058,7 +1058,7 @@ class A:
 class A:
   def bar(self): pass
 [rechecked m, n]
-[stale m, n]
+[stale n]
 [out1]
 main:2: error: "A" has no attribute "bar"
 
@@ -1149,6 +1149,214 @@ def C() -> str:
 main:1: note: In module imported here:
 tmp/m1.py:3: error: Argument 1 to "accepts_int" has incompatible type "str"; expected "int"
 
+[case testIncrementalSilentImportsWithBlatantError]
+# cmd: mypy -m main
+# flags: --silent-imports
+
+[file main.py]
+from evil import Hello
+
+[file main.py.next]
+from evil import Hello
+reveal_type(Hello())
+
+[file evil.py]
+def accept_int(x: int) -> None: pass
+accept_int("not an int")
+
+[rechecked main]
+[stale]
+[out2]
+tmp/main.py:2: error: Revealed type is 'Any'
+
+[case testIncrementalImportIsNewlySilenced]
+# cmd: mypy -m main foo
+# cmd2: mypy -m main
+# flags: --silent-imports
+
+[file main.py]
+from foo import bar
+def accept_int(x: int) -> None: pass
+accept_int(bar)
+
+[file foo.py]
+bar = 3
+
+[file foo.py.next]
+# Empty!
+
+[rechecked main]
+[stale main]
+
+[case testIncrementalSilencedModuleNoLongerCausesError]
+# cmd: mypy -m main evil
+# cmd2: mypy -m main
+# flags: --silent-imports
+
+[file main.py]
+from evil import bar
+def accept_int(x: int) -> None: pass
+accept_int(bar)
+reveal_type(bar)
+
+[file evil.py]
+bar = "str"
+
+[rechecked main]
+[stale]
+[out1]
+tmp/main.py:3: error: Argument 1 to "accept_int" has incompatible type "str"; expected "int"
+tmp/main.py:4: error: Revealed type is 'builtins.str'
+[out2]
+tmp/main.py:4: error: Revealed type is 'Any'
+
+[case testIncrementalFixedBugCausesPropagation]
+import mod1
+
+[file mod1.py]
+from mod2 import A
+val = A().makeB().makeC().foo()
+reveal_type(val)
+
+[file mod2.py]
+from mod3 import B
+class A:
+    def makeB(self) -> B: return B()
+
+[file mod3.py]
+from mod4 import C
+class B:
+    def makeC(self) -> C:
+        val = 3  # type: int
+        val = "str"   # deliberately triggering error
+        return C()
+
+[file mod3.py.next]
+from mod4 import C
+class B:
+    def makeC(self) -> C: return C()
+
+[file mod4.py]
+class C:
+    def foo(self) -> int: return 1
+
+[rechecked mod3, mod2, mod1]
+[stale mod3, mod2]
+[out1]
+tmp/mod2.py:1: note: In module imported here,
+tmp/mod1.py:1: note: ... from here,
+main:1: note: ... from here:
+tmp/mod3.py: note: In member "makeC" of class "B":
+tmp/mod3.py:5: error: Incompatible types in assignment (expression has type "str", variable has type "int")
+main:1: note: In module imported here:
+tmp/mod1.py: note: At top level:
+tmp/mod1.py:3: error: Revealed type is 'builtins.int'
+
+[out2]
+main:1: note: In module imported here:
+tmp/mod1.py:3: error: Revealed type is 'builtins.int'
+
+[case testIncrementalIncidentalChangeWithBugCausesPropagation]
+import mod1
+
+[file mod1.py]
+from mod2 import A
+val = A().makeB().makeC().foo()
+reveal_type(val)
+
+[file mod2.py]
+from mod3 import B
+class A:
+    def makeB(self) -> B: return B()
+
+[file mod3.py]
+from mod4 import C
+class B:
+    def makeC(self) -> C:
+        val = 3  # type: int
+        val = "str"   # deliberately triggering error
+        return C()
+
+[file mod4.py]
+class C:
+    def foo(self) -> int: return 1
+
+[file mod4.py.next]
+class C:
+    def foo(self) -> str: return 'a'
+
+[rechecked mod4, mod3, mod2, mod1]
+[stale mod4]
+[out1]
+tmp/mod2.py:1: note: In module imported here,
+tmp/mod1.py:1: note: ... from here,
+main:1: note: ... from here:
+tmp/mod3.py: note: In member "makeC" of class "B":
+tmp/mod3.py:5: error: Incompatible types in assignment (expression has type "str", variable has type "int")
+main:1: note: In module imported here:
+tmp/mod1.py: note: At top level:
+tmp/mod1.py:3: error: Revealed type is 'builtins.int'
+
+[out2]
+tmp/mod2.py:1: note: In module imported here,
+tmp/mod1.py:1: note: ... from here,
+main:1: note: ... from here:
+tmp/mod3.py: note: In member "makeC" of class "B":
+tmp/mod3.py:5: error: Incompatible types in assignment (expression has type "str", variable has type "int")
+main:1: note: In module imported here:
+tmp/mod1.py: note: At top level:
+tmp/mod1.py:3: error: Revealed type is 'builtins.str'
+
+[case testIncrementalIncidentalChangeWithBugFixCausesPropagation]
+import mod1
+
+[file mod1.py]
+from mod2 import A
+val = A().makeB().makeC().foo()
+reveal_type(val)
+
+[file mod2.py]
+from mod3 import B
+class A:
+    def makeB(self) -> B: return B()
+
+[file mod3.py]
+from mod4 import C
+class B:
+    def makeC(self) -> C:
+        val = 3  # type: int
+        val = "str"   # deliberately triggering error
+        return C()
+
+[file mod3.py.next]
+from mod4 import C
+class B:
+    def makeC(self) -> C: return C()
+
+[file mod4.py]
+class C:
+    def foo(self) -> int: return 1
+
+[file mod4.py.next]
+class C:
+    def foo(self) -> str: return 'a'
+
+[rechecked mod4, mod3, mod2, mod1]
+[stale mod4, mod3, mod2]
+[out1]
+tmp/mod2.py:1: note: In module imported here,
+tmp/mod1.py:1: note: ... from here,
+main:1: note: ... from here:
+tmp/mod3.py: note: In member "makeC" of class "B":
+tmp/mod3.py:5: error: Incompatible types in assignment (expression has type "str", variable has type "int")
+main:1: note: In module imported here:
+tmp/mod1.py: note: At top level:
+tmp/mod1.py:3: error: Revealed type is 'builtins.int'
+
+[out2]
+main:1: note: In module imported here:
+tmp/mod1.py:3: error: Revealed type is 'builtins.str'
+
 [case testIncrementalSilentImportsWithInnerImports]
 # cmd: mypy -m main foo
 # flags: --silent-imports
@@ -1170,7 +1378,7 @@ class MyClass:
 
 [rechecked main]
 [stale]
-[out]
+[out2]
 tmp/main.py:3: error: Revealed type is 'Any'
 
 [case testIncrementalSilentImportsWithInnerImportsAndNewFile]
@@ -1198,7 +1406,7 @@ def test() -> str: return "foo"
 
 [rechecked main, foo, unrelated]
 [stale foo, unrelated]
-[out]
+[out2]
 tmp/main.py:3: error: Revealed type is 'builtins.str'
 
 [case testIncrementalWorksWithNestedClasses]
@@ -1213,4 +1421,3 @@ class MyClass:
 
 [rechecked]
 [stale]
-[out]