Make infer_condition_value recognize the whole truth table

mypy/reachability.py

@@ -115,31 +115,44 @@ def infer_condition_value(expr: Expression, options: Options) -> int:
     MYPY_TRUE if true under mypy and false at runtime, MYPY_FALSE if
     false under mypy and true at runtime, else TRUTH_VALUE_UNKNOWN.
     """
+    if isinstance(expr, UnaryExpr) and expr.op == "not":
+        positive = infer_condition_value(expr.expr, options)
+        return inverted_truth_mapping[positive]
+
     pyversion = options.python_version
     name = ""
-    negated = False
-    alias = expr
-    if isinstance(alias, UnaryExpr):
-        if alias.op == "not":
-            expr = alias.expr
-            negated = True
+
     result = TRUTH_VALUE_UNKNOWN
     if isinstance(expr, NameExpr):
         name = expr.name
     elif isinstance(expr, MemberExpr):
         name = expr.name
-    elif isinstance(expr, OpExpr) and expr.op in ("and", "or"):
+    elif isinstance(expr, OpExpr):
+        if expr.op not in ("or", "and"):
+            return TRUTH_VALUE_UNKNOWN
+
         left = infer_condition_value(expr.left, options)
-        if (left in (ALWAYS_TRUE, MYPY_TRUE) and expr.op == "and") or (
-            left in (ALWAYS_FALSE, MYPY_FALSE) and expr.op == "or"
-        ):
-            # Either `True and <other>` or `False or <other>`: the result will
-            # always be the right-hand-side.
-            return infer_condition_value(expr.right, options)
-        else:
-            # The result will always be the left-hand-side (e.g. ALWAYS_* or
-            # TRUTH_VALUE_UNKNOWN).
-            return left
+        right = infer_condition_value(expr.right, options)
+        results = {left, right}
+        if expr.op == "or":
+            if ALWAYS_TRUE in results:
+                return ALWAYS_TRUE
+            elif MYPY_TRUE in results:
+                return MYPY_TRUE
+            elif left == right == MYPY_FALSE:
+                return MYPY_FALSE
+            elif results <= {ALWAYS_FALSE, MYPY_FALSE}:
+                return ALWAYS_FALSE
+        elif expr.op == "and":
+            if ALWAYS_FALSE in results:
+                return ALWAYS_FALSE
+            elif MYPY_FALSE in results:
+                return MYPY_FALSE
+            elif left == right == ALWAYS_TRUE:
+                return ALWAYS_TRUE
+            elif results <= {ALWAYS_TRUE, MYPY_TRUE}:
+                return MYPY_TRUE
+        return TRUTH_VALUE_UNKNOWN
     else:
         result = consider_sys_version_info(expr, pyversion)
         if result == TRUTH_VALUE_UNKNOWN:
@@ -155,8 +168,6 @@ def infer_condition_value(expr: Expression, options: Options) -> int:
             result = ALWAYS_TRUE
         elif name in options.always_false:
             result = ALWAYS_FALSE
-    if negated:
-        result = inverted_truth_mapping[result]
     return result
 
 

test-data/unit/check-unreachable-code.test

@@ -500,6 +500,82 @@ reveal_type(h)  # N: Revealed type is "builtins.bool"
 [builtins fixtures/ops.pyi]
 [out]
 
+[case testConditionalValuesBinaryOps]
+# flags: --platform linux
+import sys
+
+t_and_t = (sys.platform == 'linux' and sys.platform == 'linux') and 's'
+t_or_t = (sys.platform == 'linux' or sys.platform == 'linux') and 's'
+t_and_f = (sys.platform == 'linux' and sys.platform == 'windows') and 's'
+t_or_f = (sys.platform == 'linux' or sys.platform == 'windows') and 's'
+f_and_t = (sys.platform == 'windows' and sys.platform == 'linux') and 's'
+f_or_t = (sys.platform == 'windows' or sys.platform == 'linux') and 's'
+f_and_f = (sys.platform == 'windows' and sys.platform == 'windows') and 's'
+f_or_f = (sys.platform == 'windows' or sys.platform == 'windows') and 's'
+reveal_type(t_and_t) # N: Revealed type is "Literal['s']"
+reveal_type(t_or_t) # N: Revealed type is "Literal['s']"
+reveal_type(f_and_t) # N: Revealed type is "builtins.bool"
+reveal_type(f_or_t) # N: Revealed type is "Literal['s']"
+reveal_type(t_and_f) # N: Revealed type is "builtins.bool"
+reveal_type(t_or_f) # N: Revealed type is "Literal['s']"
+reveal_type(f_and_f) # N: Revealed type is "builtins.bool"
+reveal_type(f_or_f) # N: Revealed type is "builtins.bool"
+[builtins fixtures/ops.pyi]
+
+[case testConditionalValuesNegation]
+# flags: --platform linux
+import sys
+
+not_t = not sys.platform == 'linux' and 's'
+not_f = not sys.platform == 'windows' and 's'
+not_and_t = not (sys.platform == 'linux' and sys.platform == 'linux') and 's'
+not_and_f = not (sys.platform == 'linux' and sys.platform == 'windows') and 's'
+not_or_t = not (sys.platform == 'linux' or sys.platform == 'linux') and 's'
+not_or_f = not (sys.platform == 'windows' or sys.platform == 'windows') and 's'
+reveal_type(not_t) # N: Revealed type is "builtins.bool"
+reveal_type(not_f) # N: Revealed type is "Literal['s']"
+reveal_type(not_and_t) # N: Revealed type is "builtins.bool"
+reveal_type(not_and_f) # N: Revealed type is "Literal['s']"
+reveal_type(not_or_t) # N: Revealed type is "builtins.bool"
+reveal_type(not_or_f) # N: Revealed type is "Literal['s']"
+[builtins fixtures/ops.pyi]
+
+[case testConditionalValuesUnsupportedOps]
+# flags: --platform linux
+import sys
+
+unary_minus = -(sys.platform == 'linux') and 's'
+binary_minus = ((sys.platform == 'linux') - (sys.platform == 'linux')) and 's'
+reveal_type(unary_minus) # N: Revealed type is "Union[Literal[0], builtins.str]"
+reveal_type(binary_minus) # N: Revealed type is "Union[Literal[0], builtins.str]"
+[builtins fixtures/ops.pyi]
+
+[case testMypyFalseValuesInBinaryOps_no_empty]
+# flags: --platform linux
+import sys
+from typing import TYPE_CHECKING
+
+MYPY = 0
+
+if TYPE_CHECKING and sys.platform == 'linux':
+    def foo1() -> int: ...
+if sys.platform == 'linux' and TYPE_CHECKING:
+    def foo2() -> int: ...
+if MYPY and sys.platform == 'linux':
+    def foo3() -> int: ...
+if sys.platform == 'linux' and MYPY:
+    def foo4() -> int: ...
+
+if TYPE_CHECKING or sys.platform == 'linux':
+    def bar1() -> int: ...  # E: Missing return statement
+if sys.platform == 'linux' or TYPE_CHECKING:
+    def bar2() -> int: ...  # E: Missing return statement
+if MYPY or sys.platform == 'linux':
+    def bar3() -> int: ...  # E: Missing return statement
+if sys.platform == 'linux' or MYPY:
+    def bar4() -> int: ...  # E: Missing return statement
+[builtins fixtures/ops.pyi]
+
 [case testShortCircuitAndWithConditionalAssignment]
 # flags: --platform linux
 import sys