Make reported line and column numbers more precise (#7578)

Most notably, report more precise error locations for incompatible
return value types and incompatible default argument values.

Also add some tests.

Work towards #7053.

Author: JukkaL

mypy/checker.py

@@ -996,8 +996,13 @@ def check_default_args(self, item: FuncItem, body_is_trivial: bool) -> None:
                 msg += "tuple argument {}".format(name[12:])
             else:
                 msg += 'argument "{}"'.format(name)
-            self.check_simple_assignment(arg.variable.type, arg.initializer,
-                context=arg, msg=msg, lvalue_name='argument', rvalue_name='default',
+            self.check_simple_assignment(
+                arg.variable.type,
+                arg.initializer,
+                context=arg.initializer,
+                msg=msg,
+                lvalue_name='argument',
+                rvalue_name='default',
                 code=codes.ASSIGNMENT)
 
     def is_forward_op_method(self, method_name: str) -> bool:
@@ -3002,7 +3007,8 @@ def check_return_stmt(self, s: ReturnStmt) -> None:
                         subtype=typ,
                         supertype_label='expected',
                         supertype=return_type,
-                        context=s,
+                        context=s.expr,
+                        outer_context=s,
                         msg=message_registry.INCOMPATIBLE_RETURN_VALUE_TYPE,
                         code=codes.RETURN_VALUE)
             else:
@@ -3806,13 +3812,17 @@ def find_isinstance_check(self, node: Expression
     # Helpers
     #
 
-    def check_subtype(self, subtype: Type, supertype: Type, context: Context,
+    def check_subtype(self,
+                      subtype: Type,
+                      supertype: Type,
+                      context: Context,
                       msg: str = message_registry.INCOMPATIBLE_TYPES,
                       subtype_label: Optional[str] = None,
-                      supertype_label: Optional[str] = None, *,
-                      code: Optional[ErrorCode] = None) -> bool:
-        """Generate an error if the subtype is not compatible with
-        supertype."""
+                      supertype_label: Optional[str] = None,
+                      *,
+                      code: Optional[ErrorCode] = None,
+                      outer_context: Optional[Context] = None) -> bool:
+        """Generate an error if the subtype is not compatible with supertype."""
         if is_subtype(subtype, supertype):
             return True
 
@@ -3830,7 +3840,7 @@ def check_subtype(self, subtype: Type, supertype: Type, context: Context,
                 extra_info.append(subtype_label + ' ' + subtype_str)
             if supertype_label is not None:
                 extra_info.append(supertype_label + ' ' + supertype_str)
-            note_msg = make_inferred_type_note(context, subtype,
+            note_msg = make_inferred_type_note(outer_context or context, subtype,
                                                supertype, supertype_str)
             if isinstance(subtype, Instance) and isinstance(supertype, Instance):
                 notes = append_invariance_notes([], subtype, supertype)

mypy/fastparse.py

@@ -206,11 +206,11 @@ def parse_type_comment(type_comment: str,
     """
     try:
         typ = ast3_parse(type_comment, '<type_comment>', 'eval')
-    except SyntaxError as e:
+    except SyntaxError:
         if errors is not None:
             stripped_type = type_comment.split("#", 2)[0].strip()
             err_msg = "{} '{}'".format(TYPE_COMMENT_SYNTAX_ERROR, stripped_type)
-            errors.report(line, e.offset, err_msg, blocker=True, code=codes.SYNTAX)
+            errors.report(line, column, err_msg, blocker=True, code=codes.SYNTAX)
             return None, None
         else:
             raise

mypy/messages.py

@@ -1873,8 +1873,10 @@ def append_invariance_notes(notes: List[str], arg_type: Instance,
     return notes
 
 
-def make_inferred_type_note(context: Context, subtype: Type,
-                            supertype: Type, supertype_str: str) -> str:
+def make_inferred_type_note(context: Context,
+                            subtype: Type,
+                            supertype: Type,
+                            supertype_str: str) -> str:
     """Explain that the user may have forgotten to type a variable.
 
     The user does not expect an error if the inferred container type is the same as the return

mypy/nodes.py

@@ -559,7 +559,7 @@ def set_line(self,
                  end_line: Optional[int] = None) -> None:
         super().set_line(target, column, end_line)
 
-        if self.initializer:
+        if self.initializer and self.initializer.line < 0:
             self.initializer.set_line(self.line, self.column, self.end_line)
 
         self.variable.set_line(self.line, self.column, self.end_line)

test-data/unit/check-classes.test

@@ -2973,8 +2973,8 @@ def error(u_c: Type[U]) -> P:
     return new_pro(u_c)  # Error here, see below
 [out]
 main:11: note: Revealed type is '__main__.WizUser*'
-main:13: error: Incompatible return value type (got "U", expected "P")
 main:13: error: Value of type variable "P" of "new_pro" cannot be "U"
+main:13: error: Incompatible return value type (got "U", expected "P")
 
 [case testTypeUsingTypeCCovariance]
 from typing import Type, TypeVar

test-data/unit/check-columns.test

@@ -10,8 +10,8 @@ main:2:5: error: invalid syntax
 import typing
 def f() -> 'A':
     def g() -> 'B':
-        return A() # E:9: Incompatible return value type (got "A", expected "B")
-    return B() # E:5: Incompatible return value type (got "B", expected "A")
+        return A() # E:16: Incompatible return value type (got "A", expected "B")
+    return B() # E:12: Incompatible return value type (got "B", expected "A")
 class A: pass
 class B: pass
 
@@ -133,9 +133,12 @@ def foobar(): pass
 
 [builtins fixtures/module.pyi]
 
-[case testColumnUnexpectedKeywordArg]
+[case testColumnUnexpectedOrMissingKeywordArg]
 def f(): pass
+# TODO: Point to "x" instead
 (f(x=1)) # E:2: Unexpected keyword argument "x" for "f"
+def g(*, x: int) -> None: pass
+(g())  # E:2: Missing named argument "x" for "g"
 
 [case testColumnDefinedHere]
 class A: pass
@@ -203,6 +206,14 @@ def f(x, y): pass
 (f()) # E:2: Too few arguments for "f"
 (f(y=1)) # E:2: Missing positional argument "x" in call to "f"
 
+[case testColumnTooFewSuperArgs_python2]
+class A:
+    def f(self):
+        pass
+class B(A):
+    def f(self):   # type: () -> None
+        super().f()  # E:9: Too few arguments for "super"
+
 [case testColumnListOrDictItemHasIncompatibleType]
 from typing import List, Dict
 x: List[int] = [
@@ -258,7 +269,7 @@ if int():
 
 [case testColumnIncompatibleDefault]
 if int():
-    def f(x: int = '') -> None: # E:5: Incompatible default for argument "x" (default has type "str", argument has type "int")
+    def f(x: int = '') -> None: # E:20: Incompatible default for argument "x" (default has type "str", argument has type "int")
         pass
 
 [case testColumnMissingProtocolMember]
@@ -326,6 +337,13 @@ if int():
 main:2:11: error: Syntax error in type annotation
 main:2:11: note: Suggestion: Is there a spurious trailing comma?
 
+[case testColumnSyntaxErrorInTypeAnnotation2]
+if int():
+    # TODO: It would be better to point to the type comment
+    xyz = 0  # type: blurbnard blarb
+[out]
+main:3:5: error: syntax error in type comment 'blurbnard blarb'
+
 [case testColumnProperty]
 class A:
     @property
@@ -383,3 +401,7 @@ def f(x: T) -> T:
     n: int = '' # E:14: Incompatible types in assignment (expression has type "str", variable has type "int")
     return x
 [builtins fixtures/list.pyi]
+
+[case testColumnReturnValueExpected]
+def f() -> int:
+    return  # E:5: Return value expected