Preserve trivial bodies and nested blocks

python · JukkaL · Apr 24, 2023 · Oct 16, 2022 · Nov 5, 2022 · Nov 5, 2022
commit 20b45821f9ab565c522148bd2d7eea6e77976a08
diff --git a/mypy/fastparse.py b/mypy/fastparse.py
@@ -483,7 +483,7 @@ def get_lineno(self, node: ast3.expr | ast3.stmt) -> int:
         return node.lineno
 
     def translate_stmt_list(
-        self, stmts: Sequence[ast3.stmt], ismodule: bool = False
+            self, stmts: Sequence[ast3.stmt], *, ismodule: bool = False, can_strip: bool = False
     ) -> list[Statement]:
         # A "# type: ignore" comment before the first statement of a module
         # ignores the whole module:
@@ -519,7 +519,7 @@ def translate_stmt_list(
             node = self.visit(stmt)
             res.append(node)
 
-        if self.ignore_errors and len(stack) == 2 and stack[-2:] == ["C", "F"]:
+        if (self.ignore_errors and can_strip and len(stack) == 2 and stack[-2:] == ["C", "F"] and not is_possible_trivial_body(res)):
             v = FindAttributeAssign()
             for n in res:
                 n.accept(v)
@@ -591,9 +591,9 @@ def as_block(self, stmts: list[ast3.stmt], lineno: int) -> Block | None:
             b.set_line(lineno)
         return b
 
-    def as_required_block(self, stmts: list[ast3.stmt], lineno: int) -> Block:
+    def as_required_block(self, stmts: list[ast3.stmt], lineno: int, *, can_strip: bool = False) -> Block:
         assert stmts  # must be non-empty
-        b = Block(self.fix_function_overloads(self.translate_stmt_list(stmts)))
+        b = Block(self.fix_function_overloads(self.translate_stmt_list(stmts, can_strip=can_strip)))
         # TODO: in most call sites line is wrong (includes first line of enclosing statement)
         # TODO: also we need to set the column, and the end position here.
         b.set_line(lineno)
@@ -979,7 +979,7 @@ def do_func_def(
         end_column = getattr(n, "end_col_offset", None)
 
         self.class_and_function_stack.append("F")
-        body = self.as_required_block(n.body, lineno)
+        body = self.as_required_block(n.body, lineno, can_strip=True)
         func_def = FuncDef(n.name, args, body, func_type)
         if isinstance(func_def.type, CallableType):
             # semanal.py does some in-place modifications we want to avoid
@@ -2136,3 +2136,25 @@ def visit_member_expr(self, e: MemberExpr) -> None:
         print(e, self.lvalue)
         if self.lvalue:
             self.found = True
+
+
+def is_possible_trivial_body(s: list[Statement]) -> bool:
+    """Could the statements form a "trivial" function body, such as 'pass'?
+
+    This mimics mypy.semanal.is_trivial_body, but this runs before
+    semantic analysis so some checks must be conservative.
+    """
+    l = len(s)
+    if l == 0:
+        return False
+    i = 0
+    if isinstance(s[0], ExpressionStmt) and isinstance(s[0].expr, StrExpr):
+        # Skip docstring
+        i += 1
+    if i == l:
+        return True
+    if l > i + 1:
+        return False
+    stmt = s[i]
+    return isinstance(stmt, (PassStmt, RaiseStmt)) or (isinstance(stmt, ExpressionStmt) and
+                                          isinstance(stmt.expr, EllipsisExpr))
diff --git a/mypy/semanal.py b/mypy/semanal.py
@@ -6391,7 +6391,7 @@ def is_trivial_body(block: Block) -> bool:
     "..." (ellipsis), or "raise NotImplementedError()". A trivial body may also
     start with a statement containing just a string (e.g. a docstring).
 
-    Note: functions that raise other kinds of exceptions do not count as
+    Note: Functions that raise other kinds of exceptions do not count as
     "trivial". We use this function to help us determine when it's ok to
     relax certain checks on body, but functions that raise arbitrary exceptions
     are more likely to do non-trivial work. For example:
@@ -6401,11 +6401,18 @@ def halt(self, reason: str = ...) -> NoReturn:
 
     A function that raises just NotImplementedError is much less likely to be
     this complex.
+
+    Note: If you update this, you may also need to update
+    mypy.fastparse.is_possible_trivial_body!
     """
     body = block.body
+    if not body:
+        # Functions have empty bodies only if the body is stripped or the function is
+        # generated or deserialized. In these cases the body is unknown.
+        return False
 
     # Skip a docstring
-    if body and isinstance(body[0], ExpressionStmt) and isinstance(body[0].expr, StrExpr):
+    if isinstance(body[0], ExpressionStmt) and isinstance(body[0].expr, StrExpr):
         body = block.body[1:]
 
     if len(body) == 0:

diff --git a/test-data/unit/check-inline-config.test b/test-data/unit/check-inline-config.test
@@ -255,6 +255,8 @@ class D(C):
             # E: Call to abstract method "m3" of "C" with trivial body via super() is unsafe
         super().m4() \
             # E: Call to abstract method "m4" of "C" with trivial body via super() is unsafe
+        super().m5() \
+            # E: Call to abstract method "m5" of "C" with trivial body via super() is unsafe
 
     def m1(self) -> int:
         return 0
@@ -268,13 +270,17 @@ class D(C):
     def m4(self) -> int:
         return 0
 
+    def m5(self) -> int:
+        return 0
+
 [file m.py]
 # mypy: ignore-errors=True
 import abc
 
 class C:
     @abc.abstractmethod
     def m1(self) -> int:
+        """x"""
         return 0
 
     @abc.abstractmethod
@@ -287,3 +293,8 @@ class C:
 
     @abc.abstractmethod
     def m4(self) -> int: ...
+
+    @abc.abstractmethod
+    def m5(self) -> int:
+        """doc"""
+        ...
diff --git a/test-data/unit/parse.test b/test-data/unit/parse.test
@@ -3581,6 +3581,8 @@ class C:
     def m3(self):
         if x:
             self.y = 0
+        else:
+            x = 4
 [out]
 MypyFile:1(
   ClassDef:2(
@@ -3626,7 +3628,11 @@ MypyFile:1(
               MemberExpr:11(
                 NameExpr(self)
                 y)
-              IntExpr(0))))))))
+              IntExpr(0)))
+          Else(
+            AssignmentStmt:13(
+              NameExpr(x)
+              IntExpr(4))))))))
 
 [case testDoNotStripMethodThatDefinesAttributeWithoutAssignment]
 # mypy: ignore-errors=True
@@ -3653,7 +3659,8 @@ MypyFile:1(
             MemberExpr:4(
               NameExpr(self)
               x))
-          Block:4())))
+          Block:4(
+            PassStmt:5()))))
     FuncDef:6(
       m2
       Args(
@@ -3664,7 +3671,8 @@ MypyFile:1(
             NameExpr(self)
             y)
           NameExpr(x)
-          Block:7())))))
+          Block:7(
+            PassStmt:8()))))))
 
 [case testStripDecoratedFunctionOrMethod]
 # mypy: ignore-errors=True
@@ -3742,7 +3750,9 @@ MypyFile:1(
             Var(self)
             Var(x))
           def (self: Any, x: int?) -> None?
-          Block:4()))
+          Block:4(
+            ExpressionStmt:4(
+              Ellipsis))))
       Decorator:5(
         Var(m1)
         NameExpr(overload)
@@ -3752,7 +3762,9 @@ MypyFile:1(
             Var(self)
             Var(x))
           def (self: Any, x: str?) -> None?
-          Block:6()))
+          Block:6(
+            ExpressionStmt:6(
+              Ellipsis))))
       FuncDef:7(
         m1
         Args(
@@ -3769,7 +3781,9 @@ MypyFile:1(
             Var(self)
             Var(x))
           def (self: Any, x: int?) -> None?
-          Block:11()))
+          Block:11(
+            ExpressionStmt:11(
+              Ellipsis))))
       Decorator:12(
         Var(m2)
         NameExpr(overload)
@@ -3779,7 +3793,9 @@ MypyFile:1(
             Var(self)
             Var(x))
           def (self: Any, x: str?) -> None?
-          Block:13()))
+          Block:13(
+            ExpressionStmt:13(
+              Ellipsis))))
       FuncDef:14(
         m2
         Args(