This is still broken on Swift 3.1 Release on Ubuntu 16.10

This is still broken in the Swift 4.0 DEV snapshot for Ubuntu 14.04 released on May 29, 2017.

This doesn't appear to be related to the XCTest libraries; it's pure Swift stdlib:

http://swift.sandbox.bluemix.net/#/repl/595bac27bc7c2268561f6f27

{{let empty = ""
let nonEmpty = "\u{01}"
let result = empty == nonEmpty
print(result)
}}

The equality call shells out to this code:

https://github.com/apple/swift/blob/2b92530dfa85a017af046f3576a366e6ff914555/stdlib/public/stubs/UnicodeNormalization.cpp#L181-L215

{{
swift::_swift_stdlib_unicode_compare_utf8_utf8(const unsigned char *LeftString,
int32_t LeftLength,
const unsigned char *RightString,
int32_t RightLength) {
UCharIterator LeftIterator;
UCharIterator RightIterator;
UErrorCode ErrorCode = U_ZERO_ERROR;

uiter_setUTF8(&LeftIterator, reinterpret_cast<const char *>(LeftString), LeftLength);
uiter_setUTF8(&RightIterator, reinterpret_cast<const char *>(RightString), RightLength);

uint32_t Diff = ucol_strcollIter(GetRootCollator(),
&LeftIterator, &RightIterator, &ErrorCode);
if (U_FAILURE(ErrorCode)) {
swift::crash("ucol_strcollIter: Unexpected error doing utf8<->utf8 string comparison.");
}
return Diff;
}
}}

I suspect what's happening is the control characters (<20) are being handled in a different way in the iterator, which is why the result is being discarded. Compare:

print("" == "\u{19}") // true
print("" == "\u{20}") // false

This is still broken in the current Swift 4.1 DEV snapshots.

Has this been fixed? If so this should be closed.

I no longer see this in 4.2. 🙂