Taken from `Perl::Critic`:

A common idiom in perl for dealing with possible errors is to use `eval`
followed by a check of `$@`/`$EVAL_ERROR`:

    eval {
        ...
    };
    if ($EVAL_ERROR) {
        ...
    }

There's a problem with this: the value of `$EVAL_ERROR` (`$@`) can change
between the end of the `eval` and the `if` statement. The issue are object
destructors:

    package Foo;

    ...

    sub DESTROY {
        ...
        eval { ... };
        ...
    }

    package main;

    eval {
        my $foo = Foo->new();
        ...
    };
    if ($EVAL_ERROR) {
        ...
    }

Assuming there are no other references to `$foo` created, when the
`eval` block in `main` is exited, `Foo::DESTROY()` will be invoked,
regardless of whether the `eval` finished normally or not. If the `eval`
in `main` fails, but the `eval` in `Foo::DESTROY()` succeeds, then
`$EVAL_ERROR` will be empty by the time that the `if` is executed.
Additional issues arise if you depend upon the exact contents of
`$EVAL_ERROR` and both `eval`s fail, because the messages from both will
be concatenated.

Even if there isn't an `eval` directly in the `DESTROY()` method code,
it may invoke code that does use `eval` or otherwise affects
`$EVAL_ERROR`.

The solution is to ensure that, upon normal exit, an `eval` returns a
true value and to test that value:

    # Constructors are no problem.
    my $object = eval { Class->new() };

    # To cover the possiblity that an operation may correctly return a
    # false value, end the block with "1":
    if ( eval { something(); 1 } ) {
        ...
    }

    eval {
        ...
        1;
    }
        or do {
            # Error handling here
        };

Unfortunately, you can't use the `defined` function to test the result;
`eval` returns an empty string on failure.

Various modules have been written to take some of the pain out of
properly localizing and checking `$@`/`$EVAL_ERROR`. For example:

    use Try::Tiny;
    try {
        ...
    } catch {
        # Error handling here;
        # The exception is in $_/$ARG, not $@/$EVAL_ERROR.
    };  # Note semicolon.

"But we don't use DESTROY() anywhere in our code!" you say. That may be
the case, but do any of the third-party modules you use have them? What
about any you may use in the future or updated versions of the ones you
already use?

…errors

Improve handling of Perl's block eval errors