[perl #123963] "@<fullwidth digit>"

If an @ sign in a double-quoted string is not followed by a valid
identifier, then it is treated literally.  Or at least that is how it
was intended to work.

The lexer was actually not self-consistent.  It was treating non-ASCII
digits at valid identifiers in determining where the interpolation
started, but was not treating them as valid identifiers when actually
parsing the interpolated code.  So this would result in syntax errors,
and even crashes in some cases.

2 files changed, 5 insertions, 2 deletions

diff --git a/t/op/lex.t b/t/op/lex.t
index 7785445c44..8314f41256 100644
--- a/t/op/lex.t
+++ b/t/op/lex.t
@@ -7,7 +7,7 @@ use warnings;
 
 BEGIN { chdir 't' if -d 't'; require './test.pl'; }
 
-plan(tests => 23);
+plan(tests => 24);
 
 {
     no warnings 'deprecated';
@@ -199,3 +199,6 @@ fresh_perl_is(
    { stderr => 1 },
   '<\L\L> with no newline [perl #123802]'
 );
+
+is eval "qq'@\x{ff13}'", "\@\x{ff13}",
+  '"@<fullwidth digit>" [perl #123963]';
diff --git a/toke.c b/toke.c
index 9715f0e157..bfcb060abe 100644
--- a/toke.c
+++ b/toke.c
@@ -3056,7 +3056,7 @@ S_scan_const(pTHX_ char *start)
 	   (@foo, @::foo, @'foo, @{foo}, @$foo, @+, @-)
 	   */
 	else if (*s == '@' && s[1]) {
-	    if (isWORDCHAR_lazy_if(s+1,UTF))
+	    if (UTF ? isIDFIRST_utf8((U8*)s+1) : isWORDCHAR_A(s[1]))
 		break;
 	    if (strchr(":'{$", s[1]))
 		break;