Possibly wrong handling of regular expressions

[debarshiray]

I don't know if this is a bug in bats-assert, or a mistake on my end, but it's odd enough that I decided to file it. Please let me know if I am doing things wrong.

We use regular expressions with Bats to assert SHA256 hashes in Toolbx, and I noticed that some seemingly valid extended regular expressions are being flagged as invalid. eg., this:

load 'libs/bats-support/load'
load 'libs/bats-assert/load'

@test 'assert with --regexp \"^--> [a-z0-9]*$\"; ok!' {
  run echo "--> 1e6001"
  assert_line --index 0 --regexp "^--> [a-z0-9]*$"
}

@test 'assert with --regexp \"^--> [a-z0-9]{6}$\"; ok!' {
  run echo "--> 1e6001"
  assert_line --index 0 --regexp "^--> [a-z0-9]{6}$"
}

@test 'assert with --regexp \"^[a-z0-9]*$\"; fail!' {
  run echo "1e6001aec9c911d05bbf47d76de8d9e5bbe2e7bc17dbf772eddad775e432d7c2"
  assert_line --index 0 --regexp "^[a-z0-9]*$"  # invalid extended regular expression
}

@test 'assert with --regexp \"^[a-z0-9]{64}$\"; ok!' {
  run echo "1e6001aec9c911d05bbf47d76de8d9e5bbe2e7bc17dbf772eddad775e432d7c2"
  assert_line --index 0 --regexp "^[a-z0-9]{64}$"
}

... will lead to:

$ bats test.bats
test.bats
 ✓ assert with --regexp "^--> [a-z0-9]*$"; ok!
 ✓ assert with --regexp "^--> [a-z0-9]{6}$"; ok!
 ✗ assert with --regexp "^[a-z0-9]*$"; fail!
   (from function `assert_line' in file libs/bats-assert/src/assert_line.bash, line 170,
    in test file test.bats, line 16)
     `assert_line --index 0 --regexp "^[a-z0-9]*$"  # invalid extended regular expression' failed
   
   -- ERROR: assert_line --
   Invalid extended regular expression: `^[a-z0-9]*$'
   --
   
 ✓ assert with --regexp "^[a-z0-9]{64}$"; ok!

4 tests, 1 failure

This is the relevant code in bats-assert/src/assert_line.bash:

  # Arguments.                                                                                                                       
  local -r expected="$1"

  if (( is_mode_regexp == 1 )) && [[ '' =~ $expected ]] || (( $? == 2 )); then
    echo "Invalid extended regular expression: \`$expected'" \
    | batslib_decorate 'ERROR: assert_line' \
    | fail
    return $?
  fi

Initially, I thought that this is due to some escaping problem. So, I tried them directly in an interactive Bash session, and found something odd. The specific construct used in bats-assert to catch invalid extended regular expressions still triggers, but the expression otherwise works against a string:

$ expected="^[a-f0-9]*$"
$ if [[ '' =~ $expected ]] || (( $? == 2 )); then echo "invalid"; fi
invalid
$ if [[ '1e6001aec9c911d05bbf47d76de8d9e5bbe2e7bc17dbf772eddad775e432d7c2' =~ $expected ]]; then echo "match"; fi
match

So, I tried to tease it apart and found:

$ [[ '' =~ $expected ]]
$ echo $?
0

At this point, I have no idea why (and from where) the construct used in bats-assert gets 2 as a return status, and why another similar regular expression doesn't get flagged.

[martin-schulze-vireso]

Looks like a bug: your regex matches the empty string, so the exit code check in the or is not even called.

That means, all regexs that Match empty string are wrongly considered invalid.

[debarshiray]

Thanks for fixing this, @martin-schulze-vireso !

You were right. I overlooked that my regular expression was actually matching an empty string. I should have probably used + instead of * in the regexp.

Anyway, thanks again.