Hi,

This is a trivial patch to fix segfault occurring when generating tags for Erlang source files.


Steps to reproduce:

 1. $ wget https://erlang.org/download/otp_src_23.1.tar.gz  (~85 Mb)
 2. $ tar -xf otp_src_23.1.tar.gz
 3. $ etags otp_src_23.1/lib/*/src/*.erl
   Segmentation fault (core dumped)

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.18.9, cairo version 1.14.6)
 of 2020-11-30 built on sergey-Latitude-5480
Repository revision: 31dcc70e555482fee59df2d8aa1939360d8f8c69
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 16.04.7 LTS

Note: this bug is also present in Emacs 27 release

GDB backtrace:
(gdb) bt
#0  0x00007ffff7b5b48d in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x000000000040a7bd in mempcpy (__len=12, __src=<optimized out>, __dest=0x0)
    at /usr/include/x86_64-linux-gnu/bits/string3.h:67
#2  memcpyz (len=<optimized out>, src=<optimized out>, dest=0x0) at etags.c:149
#3  Erlang_functions (inf=0x6280a0) at etags.c:6082
#4  0x000000000040c003 in find_entries (inf=inf@entry=0x6280a0) at etags.c:1901
#5  0x000000000040c75e in process_file (fh=fh@entry=0x6280a0,
    fn=fn@entry=0x7fffffff644c "otp_src_23.1/lib/asn1/src/asn1ct_check.erl", lang=lang@entry=0x0)
    at etags.c:1722
#6  0x000000000040c9e0 in process_file_name (
    file=0x7fffffff644c "otp_src_23.1/lib/asn1/src/asn1ct_check.erl", lang=0x0) at etags.c:1668
#7  0x0000000000401c0c in main (argc=<optimized out>, argv=<optimized out>) at etags.c:1313


The attached patch fixes the above issue.

Thanks and kind regards,
Serge