seek / truncate / tell are not supported

[atoomic]

As shown with that example truncate + tell are not supported by Test::MockFile.

We should consider adding a die/warning when using it on a mocked file, before providing a correct interface for them

Using this script as a proof of concept

#!perl

use v5.32;

use Test::MockFile;

my $test_file = q[/tmp/my.test.file];

# Note: commenting this file show the broken behavior
## ---- 
# my $mock_file = Test::MockFile->file( $test_file => '' );
## ---

sub _content {
    return <<~EOS;
    # line 1
    # line 2
    # line 3
    # line 4
    # line 5
    # line 6
    EOS
}

sub setup_file {

    open( my $fh, '>', $test_file ) or die;
    print {$fh} _content();

    return 1;
}

sub cleanup_file {

    my $f = $test_file;

    open( my $fh, '+<', $f ) or return;
    {
        local $/;
        my $content = <$fh>;
    }
    
    seek( $fh, 0, 0 );
    print {$fh} "CLEAR";
    truncate( $fh, tell($fh) );
    close( $fh );

    return;
}

sub _dump_file {
    local $/;
    open( my $fh, '<', $test_file );
    my $content = <$fh>;
    
    say "#"x20;
    say $content;
    say "#"x20;

    return;
}

setup_file();
_dump_file();

cleanup_file();
_dump_file();

When run without mocking the file the output is

╰─> perl test.pl
####################
# line 1
# line 2
# line 3
# line 4
# line 5
# line 6

####################
####################
CLEAR
####################

if we now uncomment the line which mocks the file

# Note: commenting this file show the broken behavior
## ---- 
my $mock_file = Test::MockFile->file( $test_file => '' );
## ---

The output becomes

╰─> perl test.pl
####################
# line 1
# line 2
# line 3
# line 4
# line 5
# line 6

####################
####################
# line 1
# line 2
# line 3
# line 4
# line 5
# line 6
CLEAR
####################

we can see that the seek + truncate do not work as expected

[xsawyerx]

I think the difference between "bug" and "enhancement" is whether this is a described or expected behavior. Since this is not described (though makes sense to be expected), I labeled it as both "bug" and "enhancement."

[atoomic]

I agree:

To solve the bug

• either crash when using it throwing an error with the current limitation, so acknowledge & document it
• or povide an implementation

Enhancement:

• provide an implementation for it