This code:

#!/your/perl/here

use strict;
use warnings;

if (( 1) # missing closing paren
{
    my $x;
    ($x) = 'abc' =~ /(b)/;
    $x++;
}
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generates these errors:

C:\Perl\perl>perl -c syntax_error2.pl
"my" variable $x masks earlier declaration in same scope at syntax_err
+or2.pl line 9.
"my" variable $x masks earlier declaration in same scope at syntax_err
+or2.pl line 10.
syntax error at syntax_error2.pl line 7, near ") # missing closing par
+en
{"
syntax error at syntax_error2.pl line 11, near "}"
syntax_error2.pl had compilation errors.
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In the real code, several variables (which had been declared outside of the if block) were referenced, and were reported as "masking".