Error while lexing identifier if it contains an escaped newline followed by a Unicode character

[mattmanj17]

Minimal test case

int main(void) {
    int a\
ス = 42;
    return aス;
}

Godbolt example of failed compilation in clang 16
https://godbolt.org/z/TsMrbKqT6

Godbolt example of successful compilation with GCC 13.2
https://godbolt.org/z/hrzqcPKnn

Based on some debugging, I think we are looking at the '\\' in tryConsumeIdentifierUTF8Char, downstream of LexIdentifierContinue.
Perhaps that function needs to take a Size argument like tryConsumeIdentifierUCN does, so that it can correctly decode the Unicode char after the escaped newline.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[danix800]

See https://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html

[mattmanj17]

@danix800

What part in particular on that page is relevant to the case I posted?

[danix800]

The GCC extension is not relevant to this issue.

This seems to be a bug.

[shafik]

CC @cor3ntin

[cor3ntin]

@shafik https://reviews.llvm.org/D159345 :)