Bug in syntax checking causes unintended running of a function

[David Maas]

Hi! I found a bug in bash, I've checked versions 4.1 (centos 6.7), 4.2 (centos 7.2), and 4.3.30 (from the ftp site). The bug is that if you do a double parenthesis math thing with the wrong syntax, the script runs the function during what I assume is syntax checking. Demonstration script is attached.

-------------- Script --------------

#!/bin/bash

#Should be avg=((avg+6))

function neverrunme
{
    avg=0
    avg=(($avg+6))
    echo -n "This function was never called. Bash version:"
    /bin/bash --version | head -1
}

echo "Welcome to this demonstration."

-------------- Output --------------

[dm5284@juphub ~]$ ./test-file.sh
./test-file.sh: line 7: syntax error near unexpected token `('
./test-file.sh: line 7: `    avg=(($avg+6))'
This function was never called. Bash version:GNU bash, version 4.2.46(1)-release (x86_64-redhat-linux-gnu)
./test-file.sh: line 10: syntax error near unexpected token `}'
./test-file.sh: line 10: `}'

test-file.sh
Description: Bourne shell script