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[SR-14667] Deprecation warning about use of dynamicType when it's a real property #57018

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dabrahams opened this issue May 27, 2021 · 10 comments
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@dabrahams
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@dabrahams dabrahams commented May 27, 2021

Previous ID SR-14667
Radar rdar://problem/78581768
Original Reporter @dabrahams
Type Bug
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, StarterBug
Assignee ehuda (JIRA)
Priority Medium

md5: 3e9f8839ff8ccfb7c26a16ca5bcb2ae4

Issue Description:

struct X {
  let dynamicType = 0
}func f(a: X) -> Bool {
  a.dynamicType == a.dynamicType
}

Yields the warning

x.swift:6:4: error: '.dynamicType' is deprecated. Use 'type(of: ...)' instead
  a.dynamicType == a.dynamicType
   ^~~~~~~~~~~~

which I claim should only come up when no user-defined member name dynamicType exists.

@typesanitizer
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@typesanitizer typesanitizer commented May 27, 2021

@swift-ci create

@typesanitizer
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@typesanitizer typesanitizer commented May 27, 2021

Would this be a good StarterBug @xedin ?

@xedin
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@xedin xedin commented May 27, 2021

Yeah, I think it would be a good parser starter bug.

@swift-ci
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@swift-ci swift-ci commented Jun 5, 2021

Comment by Artem Burmistrov (JIRA)

I'd like to work on this, but I have a few questions:

  1. As far as my understanding goes this check should be moved from parser (where it currently is producing error based on parsed token) to semantic analysis. So my question is: where should I start digging?
  2. I kinda thought that the best place to report error could be something related to member lookup. But I struggle to understand lib/sema because it's complicated (especially since I'm a novice). Is that even a correct assumption or the error should be reported somewhere else?

@xedin
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@xedin xedin commented Jun 7, 2021

Terky (JIRA User) Yes, you are correct regarding number one from your list, warning has to be removed from the parser. Type-checker implements "special" `. dynamicType` member as `DynamicTypeOf` constraint in the solver. You'd have to move the warning to constraint solver by adding a new `ConstraintFix` and `FailureDiagnostic` implementations and recording the fix in `ConstraintSystem::simplifyDynamicTypeOfConstraint`. You can take a look at how `AllowCoercionToForceCast` is implemented for example. Let me know if you have any other questions or need help with this.

@swift-ci
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@swift-ci swift-ci commented Jun 11, 2021

Comment by Artem Burmistrov (JIRA)

@xedin, thank you for the help. I looked at `DynamicTypeOf` and as far as my understanding goes it is produced from the `type(of: )`, not from the `.dynamicType` member. I also tried to remove error diagnostics from the parser and place the breakpoint in the `ConstraintSystem::simplifyConstraint`. But from what I got there was no `DynamicTypeOf` constraint kind. Is `dynamicType` member even supported as a special member? Also if I remove the `dynamicType` property declaration from the example it would produce the `MissingMemberFailure`. Am I missing something or there should be another place to produce `ConstraintFix`?

@xedin
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@xedin xedin commented Jun 11, 2021

Terky (JIRA User) Once you have removed the diagnostic from the parser, you need to move it to the DiagnosticsSema.def and produce it in `MissingMemberFailure::diagnose` instead of a default missing member diagnostic. Sorry I forgot that `DynamicTypeOf` is only used for `type(of: ...)` since I thought, for some reason, that this was a warning and not an error...

@CodaFi
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@CodaFi CodaFi commented Aug 26, 2021

It's been 5 years, and `dynamicType` was not exactly a popular feature when it was first introduced. I think we can probably just remove this diagnostic altogether. The chance of confusion stemming from the fallback diagnostic of

value of type 'X' has no member 'dynamicType'

is low. I say we just remove the special case from the parser.

@xedin
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@xedin xedin commented Aug 26, 2021

That sounds good to me!

@swift-ci
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@swift-ci swift-ci commented Sep 24, 2021

Comment by Ehud Adler (JIRA)

Merged. PR: #39443

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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