@discardableResult works with try and try!, but not try?

[AnthonyLatsis]

Description

No response

Reproduction

@discardableResult
func foo() throws -> Int {}

func test() {
  try? foo() // warning: result of 'try?' is unused [expression_unused_optional_try]
}

Expected behavior

No warning

Environment

Swift version 5.11-dev (Swift 11ef6e5)

Additional information

No response

[li3zhen1]

Hi, I think I can fix this. but in lib/Sema/TypeCheckStmt.cpp there was a commit from 9 years ago:

Always warn when 'try?' is discarded.
rdar://problem/22195906
Swift SVN r31090

(as as? as! are all treated as non-discardable, and I feel like it's reasonable if try? behaves like them.)

I also found another corner case with discardable computed member reference, not sure if it's a expected behavior:

struct S {
    var s: S {
        @discardableResult
        get {
            return self
        }
    }
}

24 │
25 │ func test() {
26 │     S().s
   │         ╰─ warning: expression of type 'S' is unused
27 │ }
28 │

[AnthonyLatsis]

there was a commit from 9 years ago:

Always warn when 'try?' is discarded.
rdar://problem/22195906
Swift SVN r31090

Apparently, that was supposed to mean "warn even if the call returns Void", perhaps to encourage error handling or explicit discarding. @discardableResult should override these rules.

I also found another corner case with discardable computed member reference, not sure if it's a expected behavior

Is that even a reasonable thing to do? Either way the current behavior is a bug. Could you report it?

---

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