Major fixes and new features

venv/lib/python3.12/site-packages/mypy/reachability.py

@@ -0,0 +1,362 @@
+"""Utilities related to determining the reachability of code (in semantic analysis)."""
+
+from __future__ import annotations
+
+from typing import Final, Tuple, TypeVar
+
+from mypy.literals import literal
+from mypy.nodes import (
+    LITERAL_YES,
+    AssertStmt,
+    Block,
+    CallExpr,
+    ComparisonExpr,
+    Expression,
+    FuncDef,
+    IfStmt,
+    Import,
+    ImportAll,
+    ImportFrom,
+    IndexExpr,
+    IntExpr,
+    MatchStmt,
+    MemberExpr,
+    NameExpr,
+    OpExpr,
+    SliceExpr,
+    StrExpr,
+    TupleExpr,
+    UnaryExpr,
+)
+from mypy.options import Options
+from mypy.patterns import AsPattern, OrPattern, Pattern
+from mypy.traverser import TraverserVisitor
+
+# Inferred truth value of an expression.
+ALWAYS_TRUE: Final = 1
+MYPY_TRUE: Final = 2  # True in mypy, False at runtime
+ALWAYS_FALSE: Final = 3
+MYPY_FALSE: Final = 4  # False in mypy, True at runtime
+TRUTH_VALUE_UNKNOWN: Final = 5
+
+inverted_truth_mapping: Final = {
+    ALWAYS_TRUE: ALWAYS_FALSE,
+    ALWAYS_FALSE: ALWAYS_TRUE,
+    TRUTH_VALUE_UNKNOWN: TRUTH_VALUE_UNKNOWN,
+    MYPY_TRUE: MYPY_FALSE,
+    MYPY_FALSE: MYPY_TRUE,
+}
+
+reverse_op: Final = {"==": "==", "!=": "!=", "<": ">", ">": "<", "<=": ">=", ">=": "<="}
+
+
+def infer_reachability_of_if_statement(s: IfStmt, options: Options) -> None:
+    for i in range(len(s.expr)):
+        result = infer_condition_value(s.expr[i], options)
+        if result in (ALWAYS_FALSE, MYPY_FALSE):
+            # The condition is considered always false, so we skip the if/elif body.
+            mark_block_unreachable(s.body[i])
+        elif result in (ALWAYS_TRUE, MYPY_TRUE):
+            # This condition is considered always true, so all of the remaining
+            # elif/else bodies should not be checked.
+            if result == MYPY_TRUE:
+                # This condition is false at runtime; this will affect
+                # import priorities.
+                mark_block_mypy_only(s.body[i])
+            for body in s.body[i + 1 :]:
+                mark_block_unreachable(body)
+
+            # Make sure else body always exists and is marked as
+            # unreachable so the type checker always knows that
+            # all control flow paths will flow through the if
+            # statement body.
+            if not s.else_body:
+                s.else_body = Block([])
+            mark_block_unreachable(s.else_body)
+            break
+
+
+def infer_reachability_of_match_statement(s: MatchStmt, options: Options) -> None:
+    for i, guard in enumerate(s.guards):
+        pattern_value = infer_pattern_value(s.patterns[i])
+
+        if guard is not None:
+            guard_value = infer_condition_value(guard, options)
+        else:
+            guard_value = ALWAYS_TRUE
+
+        if pattern_value in (ALWAYS_FALSE, MYPY_FALSE) or guard_value in (
+            ALWAYS_FALSE,
+            MYPY_FALSE,
+        ):
+            # The case is considered always false, so we skip the case body.
+            mark_block_unreachable(s.bodies[i])
+        elif pattern_value in (ALWAYS_FALSE, MYPY_TRUE) and guard_value in (
+            ALWAYS_TRUE,
+            MYPY_TRUE,
+        ):
+            for body in s.bodies[i + 1 :]:
+                mark_block_unreachable(body)
+
+        if guard_value == MYPY_TRUE:
+            # This condition is false at runtime; this will affect
+            # import priorities.
+            mark_block_mypy_only(s.bodies[i])
+
+
+def assert_will_always_fail(s: AssertStmt, options: Options) -> bool:
+    return infer_condition_value(s.expr, options) in (ALWAYS_FALSE, MYPY_FALSE)
+
+
+def infer_condition_value(expr: Expression, options: Options) -> int:
+    """Infer whether the given condition is always true/false.
+
+    Return ALWAYS_TRUE if always true, ALWAYS_FALSE if always false,
+    MYPY_TRUE if true under mypy and false at runtime, MYPY_FALSE if
+    false under mypy and true at runtime, else TRUTH_VALUE_UNKNOWN.
+    """
+    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"):
+        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
+    else:
+        result = consider_sys_version_info(expr, pyversion)
+        if result == TRUTH_VALUE_UNKNOWN:
+            result = consider_sys_platform(expr, options.platform)
+    if result == TRUTH_VALUE_UNKNOWN:
+        if name == "PY2":
+            result = ALWAYS_FALSE
+        elif name == "PY3":
+            result = ALWAYS_TRUE
+        elif name == "MYPY" or name == "TYPE_CHECKING":
+            result = MYPY_TRUE
+        elif name in options.always_true:
+            result = ALWAYS_TRUE
+        elif name in options.always_false:
+            result = ALWAYS_FALSE
+    if negated:
+        result = inverted_truth_mapping[result]
+    return result
+
+
+def infer_pattern_value(pattern: Pattern) -> int:
+    if isinstance(pattern, AsPattern) and pattern.pattern is None:
+        return ALWAYS_TRUE
+    elif isinstance(pattern, OrPattern) and any(
+        infer_pattern_value(p) == ALWAYS_TRUE for p in pattern.patterns
+    ):
+        return ALWAYS_TRUE
+    else:
+        return TRUTH_VALUE_UNKNOWN
+
+
+def consider_sys_version_info(expr: Expression, pyversion: tuple[int, ...]) -> int:
+    """Consider whether expr is a comparison involving sys.version_info.
+
+    Return ALWAYS_TRUE, ALWAYS_FALSE, or TRUTH_VALUE_UNKNOWN.
+    """
+    # Cases supported:
+    # - sys.version_info[<int>] <compare_op> <int>
+    # - sys.version_info[:<int>] <compare_op> <tuple_of_n_ints>
+    # - sys.version_info <compare_op> <tuple_of_1_or_2_ints>
+    #   (in this case <compare_op> must be >, >=, <, <=, but cannot be ==, !=)
+    if not isinstance(expr, ComparisonExpr):
+        return TRUTH_VALUE_UNKNOWN
+    # Let's not yet support chained comparisons.
+    if len(expr.operators) > 1:
+        return TRUTH_VALUE_UNKNOWN
+    op = expr.operators[0]
+    if op not in ("==", "!=", "<=", ">=", "<", ">"):
+        return TRUTH_VALUE_UNKNOWN
+
+    index = contains_sys_version_info(expr.operands[0])
+    thing = contains_int_or_tuple_of_ints(expr.operands[1])
+    if index is None or thing is None:
+        index = contains_sys_version_info(expr.operands[1])
+        thing = contains_int_or_tuple_of_ints(expr.operands[0])
+        op = reverse_op[op]
+    if isinstance(index, int) and isinstance(thing, int):
+        # sys.version_info[i] <compare_op> k
+        if 0 <= index <= 1:
+            return fixed_comparison(pyversion[index], op, thing)
+        else:
+            return TRUTH_VALUE_UNKNOWN
+    elif isinstance(index, tuple) and isinstance(thing, tuple):
+        lo, hi = index
+        if lo is None:
+            lo = 0
+        if hi is None:
+            hi = 2
+        if 0 <= lo < hi <= 2:
+            val = pyversion[lo:hi]
+            if len(val) == len(thing) or len(val) > len(thing) and op not in ("==", "!="):
+                return fixed_comparison(val, op, thing)
+    return TRUTH_VALUE_UNKNOWN
+
+
+def consider_sys_platform(expr: Expression, platform: str) -> int:
+    """Consider whether expr is a comparison involving sys.platform.
+
+    Return ALWAYS_TRUE, ALWAYS_FALSE, or TRUTH_VALUE_UNKNOWN.
+    """
+    # Cases supported:
+    # - sys.platform == 'posix'
+    # - sys.platform != 'win32'
+    # - sys.platform.startswith('win')
+    if isinstance(expr, ComparisonExpr):
+        # Let's not yet support chained comparisons.
+        if len(expr.operators) > 1:
+            return TRUTH_VALUE_UNKNOWN
+        op = expr.operators[0]
+        if op not in ("==", "!="):
+            return TRUTH_VALUE_UNKNOWN
+        if not is_sys_attr(expr.operands[0], "platform"):
+            return TRUTH_VALUE_UNKNOWN
+        right = expr.operands[1]
+        if not isinstance(right, StrExpr):
+            return TRUTH_VALUE_UNKNOWN
+        return fixed_comparison(platform, op, right.value)
+    elif isinstance(expr, CallExpr):
+        if not isinstance(expr.callee, MemberExpr):
+            return TRUTH_VALUE_UNKNOWN
+        if len(expr.args) != 1 or not isinstance(expr.args[0], StrExpr):
+            return TRUTH_VALUE_UNKNOWN
+        if not is_sys_attr(expr.callee.expr, "platform"):
+            return TRUTH_VALUE_UNKNOWN
+        if expr.callee.name != "startswith":
+            return TRUTH_VALUE_UNKNOWN
+        if platform.startswith(expr.args[0].value):
+            return ALWAYS_TRUE
+        else:
+            return ALWAYS_FALSE
+    else:
+        return TRUTH_VALUE_UNKNOWN
+
+
+Targ = TypeVar("Targ", int, str, Tuple[int, ...])
+
+
+def fixed_comparison(left: Targ, op: str, right: Targ) -> int:
+    rmap = {False: ALWAYS_FALSE, True: ALWAYS_TRUE}
+    if op == "==":
+        return rmap[left == right]
+    if op == "!=":
+        return rmap[left != right]
+    if op == "<=":
+        return rmap[left <= right]
+    if op == ">=":
+        return rmap[left >= right]
+    if op == "<":
+        return rmap[left < right]
+    if op == ">":
+        return rmap[left > right]
+    return TRUTH_VALUE_UNKNOWN
+
+
+def contains_int_or_tuple_of_ints(expr: Expression) -> None | int | tuple[int, ...]:
+    if isinstance(expr, IntExpr):
+        return expr.value
+    if isinstance(expr, TupleExpr):
+        if literal(expr) == LITERAL_YES:
+            thing = []
+            for x in expr.items:
+                if not isinstance(x, IntExpr):
+                    return None
+                thing.append(x.value)
+            return tuple(thing)
+    return None
+
+
+def contains_sys_version_info(expr: Expression) -> None | int | tuple[int | None, int | None]:
+    if is_sys_attr(expr, "version_info"):
+        return (None, None)  # Same as sys.version_info[:]
+    if isinstance(expr, IndexExpr) and is_sys_attr(expr.base, "version_info"):
+        index = expr.index
+        if isinstance(index, IntExpr):
+            return index.value
+        if isinstance(index, SliceExpr):
+            if index.stride is not None:
+                if not isinstance(index.stride, IntExpr) or index.stride.value != 1:
+                    return None
+            begin = end = None
+            if index.begin_index is not None:
+                if not isinstance(index.begin_index, IntExpr):
+                    return None
+                begin = index.begin_index.value
+            if index.end_index is not None:
+                if not isinstance(index.end_index, IntExpr):
+                    return None
+                end = index.end_index.value
+            return (begin, end)
+    return None
+
+
+def is_sys_attr(expr: Expression, name: str) -> bool:
+    # TODO: This currently doesn't work with code like this:
+    # - import sys as _sys
+    # - from sys import version_info
+    if isinstance(expr, MemberExpr) and expr.name == name:
+        if isinstance(expr.expr, NameExpr) and expr.expr.name == "sys":
+            # TODO: Guard against a local named sys, etc.
+            # (Though later passes will still do most checking.)
+            return True
+    return False
+
+
+def mark_block_unreachable(block: Block) -> None:
+    block.is_unreachable = True
+    block.accept(MarkImportsUnreachableVisitor())
+
+
+class MarkImportsUnreachableVisitor(TraverserVisitor):
+    """Visitor that flags all imports nested within a node as unreachable."""
+
+    def visit_import(self, node: Import) -> None:
+        node.is_unreachable = True
+
+    def visit_import_from(self, node: ImportFrom) -> None:
+        node.is_unreachable = True
+
+    def visit_import_all(self, node: ImportAll) -> None:
+        node.is_unreachable = True
+
+
+def mark_block_mypy_only(block: Block) -> None:
+    block.accept(MarkImportsMypyOnlyVisitor())
+
+
+class MarkImportsMypyOnlyVisitor(TraverserVisitor):
+    """Visitor that sets is_mypy_only (which affects priority)."""
+
+    def visit_import(self, node: Import) -> None:
+        node.is_mypy_only = True
+
+    def visit_import_from(self, node: ImportFrom) -> None:
+        node.is_mypy_only = True
+
+    def visit_import_all(self, node: ImportAll) -> None:
+        node.is_mypy_only = True
+
+    def visit_func_def(self, node: FuncDef) -> None:
+        node.is_mypy_only = True