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[SR-2041] subtyping of tuple expressions is not implemented properly, causing compiler crashes #44650

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swift-ci opened this issue Jul 10, 2016 · 2 comments
Open

[SR-2041] subtyping of tuple expressions is not implemented properly, causing compiler crashes #44650

swift-ci opened this issue Jul 10, 2016 · 2 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself crash Bug: A crash, i.e., an abnormal termination of software type checker Area → compiler: Semantic analysis

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@swift-ci
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Previous ID SR-2041
Radar None
Original Reporter gold_hat (JIRA User)
Type Bug
Environment

Swift 2.2

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, CompilerCrash, TypeChecker
Assignee None
Priority Medium

md5: a471581c51906b9e1b69b04097bac50d

Issue Description:

Here is one example of code that will crash the compiler:

let _ = "a".isEmpty ? (2, 3) as (Int, Int) : (2, 3) as (Int?, Int?)

I believe this is caused by an inconsistent application of the principle of subtyping to the components of tuples. This inconsistency is illustrated by these examples:

class C {}
let _ = (C(), 3 as Int) as (Any, Int?)  // WORKS FINE
let _ = (C(), 3) as (C, Int) as (Any, Int?)  // TYPE ERROR
let _ = ((C(), 3), true).0 as (Any, Int?)  // TYPE ERROR

This inconsistency is likely also responsible for the rather comical output when you compile and run this code:

if (2 as Int, 3 as Int) is (Int?, Int?) {
  print("test is true")
} else {
  print("test is false")
}

Here is the output I get:

test.swift:43:25: warning: 'is' test is always true
if (2 as Int, 3 as Int) is (Int?, Int?) {
                        ^
test is false
@swift-ci
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Comment by Aaron Bohannon (JIRA)

It may not be obvious from the examples above, but this issue is also highly relevant in code of a more practical sort. In fact, I'm quite surprised that nobody has reported this issue before, considering that it affects code like this:

func returnPair() -> (C, Int) { return (C(), 3) }
var x: Int? = nil

x = returnPair().1  // WORKS FINE

(_, x) = returnPair()  // TYPE ERROR

@CodaFi
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CodaFi commented Jul 11, 2016

It's not a subtyping inconsistency so much as a poor application of optional coercion in operators that is at play here (one that I wish we would remove).

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@AnthonyLatsis AnthonyLatsis added the crash Bug: A crash, i.e., an abnormal termination of software label Dec 12, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself crash Bug: A crash, i.e., an abnormal termination of software type checker Area → compiler: Semantic analysis
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@CodaFi @swift-ci @AnthonyLatsis