Closed
Description
Description
For some reason, UTF8Span.span behaves quite differently from using UTF8View.span where temporary values are concerned.
Reproduction
func intUTF8SpanCount1(_ i: Int) -> Int {
let span = String(i).utf8Span
return span.count
}
func intUTF8SpanCount2(_ i: Int) -> Int {
let span = String(i).utf8Span.span
return span.count
}
#if false
func intUTF8SpanCount3(_ i: Int) -> Int {
let span = String(i).utf8.span
return span.count
}
#endif(also here: https://swift.godbolt.org/z/zxo6b358f)
After switching the #if clause to true, the third case will fail to compile with a correct escape diagnostic:
<source>:13:9: error: lifetime-dependent variable 'span' escapes its scope
11 | #if true
12 | func intUTF8SpanCount3(_ i: Int) -> Int {
13 | let span = String(i).utf8.span
| | `- note: it depends on the lifetime of this parent value
| `- error: lifetime-dependent variable 'span' escapes its scope
14 | return span.count
| `- note: this use of the lifetime-dependent value is out of scope
15 | }
16 | #endif
Compiler returned: 1
Expected behavior
The first two should also produce an escape diagnostic.
Environment
swift-DEVELOPMENT-SNAPSHOT-2025-06-03-a
Code example: https://swift.godbolt.org/z/zxo6b358f
Additional information
Related to: #81931
Also tracked as: rdar://152660149