Improve message when function is missing return type #6773

allisonking · 2019-05-06T16:16:46Z

ilevkivskyi

Thank you! This looks good, but I have couple small suggestions.

ilevkivskyi · 2019-05-06T18:23:51Z

mypy/checker.py

@@ -984,7 +984,12 @@ def is_unannotated_any(t: Type) -> bool:
        check_incomplete_defs = self.options.disallow_incomplete_defs and has_explicit_annotation
        if show_untyped and (self.options.disallow_untyped_defs or check_incomplete_defs):
            if fdef.type is None and self.options.disallow_untyped_defs:
-                self.fail(message_registry.FUNCTION_TYPE_EXPECTED, fdef)
+                if (not len(fdef.arguments) or


You don'y need len(...) here, just not fdef.arguments.

ilevkivskyi · 2019-05-06T18:24:59Z

mypy/checker.py

@@ -984,7 +984,12 @@ def is_unannotated_any(t: Type) -> bool:
        check_incomplete_defs = self.options.disallow_incomplete_defs and has_explicit_annotation
        if show_untyped and (self.options.disallow_untyped_defs or check_incomplete_defs):
            if fdef.type is None and self.options.disallow_untyped_defs:
-                self.fail(message_registry.FUNCTION_TYPE_EXPECTED, fdef)
+                if (not len(fdef.arguments) or
+                        (len(fdef.arg_names) == 1 and 'self' in fdef.arg_names)):


fdef.arg_names[0] == 'self' would be more straightforward. Also maybe you should check for both self and cls.

ilevkivskyi · 2019-05-06T18:29:33Z

mypy/checker.py

+                if (not len(fdef.arguments) or
+                        (len(fdef.arg_names) == 1 and 'self' in fdef.arg_names)):
+                    self.fail(message_registry.RETURN_TYPE_EXPECTED_DISALLOW_UNTYPED, fdef)
+                    self.note('Use "-> None" if function does not return a value', fdef)


I would only show this note if the function body doesn't have non-trivial return statements (i.e. return x not just plain return).

okay sounds good-- could you point me to how to find if there's a return value?

You probably have to create a new StatementVisitor that traverses fdef.body looking for any ReturnStmt instances whose expr is not None.

(And don't take my word for it. :-)

You can use stubgen.has_return_statement() (Maybe also move it to some common file like nodes.py?)

(Fix: srubgen -> stubgen)

I took a stab at implementing this in nodes.py... let me know if it's reasonable! 😬

ilevkivskyi · 2019-05-06T18:31:18Z

mypy/message_registry.py

@@ -74,6 +74,8 @@
 FUNCTION_TYPE_EXPECTED = "Function is missing a type annotation"  # type: Final
 ONLY_CLASS_APPLICATION = "Type application is only supported for generic classes"  # type: Final
 RETURN_TYPE_EXPECTED = "Function is missing a return type annotation"  # type: Final
+RETURN_TYPE_EXPECTED_DISALLOW_UNTYPED = \
+    "Function must have a return type annotation ('disallow_untyped_defs' enabled)"  # type: Final


Although it is mentioned in the issue, I would not mention the name of option of the flag in the error message. It may easily get out of sync. So I would remove the part in (...).

gvanrossum · 2019-05-06T18:39:09Z

mypy/checker.py

@@ -984,7 +984,12 @@ def is_unannotated_any(t: Type) -> bool:
        check_incomplete_defs = self.options.disallow_incomplete_defs and has_explicit_annotation
        if show_untyped and (self.options.disallow_untyped_defs or check_incomplete_defs):
            if fdef.type is None and self.options.disallow_untyped_defs:
-                self.fail(message_registry.FUNCTION_TYPE_EXPECTED, fdef)
+                if (not len(fdef.arguments) or
+                        (len(fdef.arg_names) == 1 and 'self' in fdef.arg_names)):


@JukkaL or @ilevkivskyi Is there a more reliable way to tell whether something's a method? Some (unusual) code bases use a different name instead of self, and class methods also aren't covered by this test.

It's also possible to scan the body to see whether occurrences of return have a value or not on them (though I don't know how practical that is from this context).

I think for self there is actually one: Var.is_self. I am not sure we have the same for cls.

Thanks! I tried checking for fdef.arguments[0].variable.is_self here but it seems like I always get False. I couldn't find where is_self was being set-- for now I have this checking for the strings self and cls but agree it's not great

It may be because if a function is missing type annotation, then we don't analyze it at all during semantic analysis. I think it is OK to rely on the argument name, since this is needed only to tweak the error message, and not to decide whether we need to emit the error.

ilevkivskyi

Thanks for updates! This is almost ready, I have few more comments.

ilevkivskyi · 2019-05-07T13:31:51Z

mypy/checker.py

@@ -984,7 +984,14 @@ def is_unannotated_any(t: Type) -> bool:
        check_incomplete_defs = self.options.disallow_incomplete_defs and has_explicit_annotation
        if show_untyped and (self.options.disallow_untyped_defs or check_incomplete_defs):
            if fdef.type is None and self.options.disallow_untyped_defs:
-                self.fail(message_registry.FUNCTION_TYPE_EXPECTED, fdef)
+                if (not fdef.arguments or (len(fdef.arguments) == 1 and 
+                        #(fdef.arguments[0].variable.is_self or fdef.arg_names[0] == 'cls'))):


This comment is not needed.

ilevkivskyi · 2019-05-07T13:33:24Z

mypy/nodes.py

@@ -1101,6 +1111,19 @@ def __init__(self, expr: Optional[Expression]) -> None:
    def accept(self, visitor: StatementVisitor[T]) -> T:
        return visitor.visit_return_stmt(self)

+class ReturnSeeker(StatementVisitor):


StatementVisitor[None]

ilevkivskyi · 2019-05-07T13:34:40Z

mypy/nodes.py

+    def visit_return_stmt(self, o: ReturnStmt) -> None:
+        if (o.expr is None or isinstance(o.expr, NameExpr) and o.expr.name == 'None'):
+            return
+        self.found = True


This causes a bunch of code duplication with stubgen.py. Why don't you remove this class (and corresponding helper) from there and also use the added method there?

ilevkivskyi · 2019-05-07T13:35:47Z

test-data/unit/cmdline.test

@@ -1063,7 +1063,8 @@ disallow_any_generics = True
 def get_tasks(self):
    return 'whatever'
 [out]
-a.py:1: error: Function is missing a type annotation
+a.py:1: error: Function is missing a return type annotation
+a.py:1: note: Use "-> None" if function does not return a value


This should not be here because method returns a string (see CI failures).

…missing-return-type-message

ilevkivskyi

Thank you! I have just two more comments.

ilevkivskyi · 2019-05-08T12:49:49Z

mypy/nodes.py

+        pass
+
+    def visit_exec_stmt(self, o: ExecStmt) -> None:
+        pass


Why do you need all these dummy methods? Maybe instead just inherit from mypy.traverser.TraverserVisitor?

I was having trouble importing the mypy.traverser.TraverserVisitor class, I believe because traverser.py also imports from nodes.py?

mypy/test/testcheck.py:9: in <module> from mypy import build mypy/build.py:36: in <module> from mypy.nodes import MypyFile, ImportBase, Import, ImportFrom, ImportAll, SymbolTable mypy/nodes.py:20: in <module> from mypy.traverser import TraverserVisitor mypy/traverser.py:4: in <module> from mypy.nodes import ( E ImportError: cannot import name 'Block' from 'mypy.nodes' (mypy/nodes.py)

Hm, yes, this would cause an import cycle. What if you instead keep this a function (not a method) and move it (together with the visitor class) to mypy.traverser and then import it from this common place in both cases (in stubgen.py and in checker.py)? I think this would be a reasonable solution.

ilevkivskyi · 2019-05-08T12:50:25Z

mypy/stubgen.py

@@ -97,6 +97,7 @@ class Options:

    This class is mutable to simplify testing.
    """
+


This empty line and a bunch below look unrelated to the PR

whoops-- turned off my autoformatter :)

ilevkivskyi

Thank you for all the work! This looks ready now.

allisonking added 2 commits May 6, 2019 10:53

Improve message when function is missing return type

ebc64f6

update tests with new error message

6da0d3d

ilevkivskyi reviewed May 6, 2019

View reviewed changes

gvanrossum reviewed May 6, 2019

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check for return statement to change error text

a879bbc

ilevkivskyi reviewed May 7, 2019

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allisonking added 3 commits May 7, 2019 20:16

replace duplicate functions in stubgen.py with ones in nodes.py

2a14246

Merge remote-tracking branch 'upstream/master' into fix/improve-func-…

92fb150

…missing-return-type-message

fix 3.8 test

61dda8a

ilevkivskyi reviewed May 8, 2019

View reviewed changes

allisonking added 2 commits May 8, 2019 20:32

move ReturnSeeker to traverser.py

85e37bd

undo line break

a2b82f4

ilevkivskyi approved these changes May 9, 2019

View reviewed changes

ilevkivskyi merged commit 9c74efd into python:master May 9, 2019

		@@ -97,6 +97,7 @@ class Options:

		This class is mutable to simplify testing.
		"""

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Improve message when function is missing return type #6773

Improve message when function is missing return type #6773

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allisonking commented May 6, 2019

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ilevkivskyi May 6, 2019 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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ilevkivskyi May 6, 2019 •

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