Support typing.TYPE_CHECKING.

Fixes python#2165. This is not completely correct (it'll trigger on *any* variable named TYPE_CHECKING) but I think that's acceptable. We should be able to phase out MYPY once this is in the next release.
gitter-badger · Sep 21, 2016 · 345a457 · 345a457
1 parent 60a99a7
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Showing 4 changed files with 46 additions and 1 deletion.
diff --git a/mypy/build.py b/mypy/build.py
@@ -1472,6 +1472,7 @@ def dispatch(sources: List[BuildSource], manager: BuildManager) -> None:
     manager.log("Loaded graph with %d nodes" % len(graph))
     process_graph(graph, manager)
     if manager.options.warn_unused_ignores:
+        # TODO: This could also be a per-file option.
         manager.errors.generate_unused_ignore_notes()
 
 

diff --git a/mypy/semanal.py b/mypy/semanal.py
@@ -3023,7 +3023,7 @@ def infer_if_condition_value(expr: Node, pyversion: Tuple[int, int], platform: s
             result = ALWAYS_TRUE if pyversion[0] == 2 else ALWAYS_FALSE
         elif name == 'PY3':
             result = ALWAYS_TRUE if pyversion[0] == 3 else ALWAYS_FALSE
-        elif name == 'MYPY':
+        elif name == 'MYPY' or name == 'TYPE_CHECKING':
             result = ALWAYS_TRUE
     if negated:
         if result == ALWAYS_TRUE:

diff --git a/test-data/unit/check-unreachable-code.test b/test-data/unit/check-unreachable-code.test
@@ -90,6 +90,48 @@ else:
     None + ''
 [builtins fixtures/bool.pyi]
 
+[case testTypeCheckingConditional]
+import typing
+if typing.TYPE_CHECKING:
+    import pow123 # E
+else:
+    import xyz753
+[out]
+main:3: error: Cannot find module named 'pow123'
+main:3: note: (Perhaps setting MYPYPATH or using the "--silent-imports" flag would help)
+
+[case testTypeCheckingConditionalFromImport]
+from typing import TYPE_CHECKING
+if TYPE_CHECKING:
+    import pow123 # E
+else:
+    import xyz753
+[out]
+main:3: error: Cannot find module named 'pow123'
+main:3: note: (Perhaps setting MYPYPATH or using the "--silent-imports" flag would help)
+
+[case testNegatedTypeCheckingConditional]
+import typing
+if not typing.TYPE_CHECKING:
+    import pow123 # E
+else:
+    import xyz753
+[builtins fixtures/bool.pyi]
+[out]
+main:5: error: Cannot find module named 'xyz753'
+main:5: note: (Perhaps setting MYPYPATH or using the "--silent-imports" flag would help)
+
+[case testUndefinedTypeCheckingConditional]
+if not TYPE_CHECKING: # E
+    import pow123
+else:
+    import xyz753
+[builtins fixtures/bool.pyi]
+[out]
+main:1: error: Name 'TYPE_CHECKING' is not defined
+main:4: error: Cannot find module named 'xyz753'
+main:4: note: (Perhaps setting MYPYPATH or using the "--silent-imports" flag would help)
+
 [case testConditionalClassDefPY3]
 def f(): pass
 PY3 = f()

diff --git a/test-data/unit/lib-stub/typing.pyi b/test-data/unit/lib-stub/typing.pyi
@@ -84,3 +84,5 @@ def NewType(name: str, tp: Type[T]) -> Callable[[T], T]:
     def new_type(x):
         return x
     return new_type
+
+TYPE_CHECKING = 1