Use of uninitialized value $less_charset in pattern match

[felsenhower]

I am trying to use diff-so-fancy on a system with macOS (Darwin 19.6.0), perl v5.18.4 and git version 2.24.3 (Apple Git-128).
When using it normally (like diff -u f1 f2 | diff-so-fancy), everything seems to be in order. But when setting up git like specified in the README, I get the following:

$ git diff     
Use of uninitialized value $less_charset in pattern match (m//) at /path/to/diff-so-fancy line 530, <STDIN> line 28.

This happens in the function should_print_unicode. I was trying to work around the issue by returning 0 or 1 in the first line of te function, which only leads to the following message:

$ git diff
"my" variable $columns_to_remove masks earlier declaration in same scope at /path/to/diff-so-fancy line 568.

Is this a problem with the installed dependencies or rather with diff-so-fancy?

[scottchiefbaker]

This is almost certainly an issue with d-s-f. What version do you have? We fixed a less bug not to long ago I wonder if you have an old version.

[felsenhower]

I am using the newest commit on master e5bddde

[scottchiefbaker]

Can you give me the output of diff-so-fancy --debug please?

[felsenhower]

It seems like the output is identical to the output of when I start d-s-f without parameters:

$ diff-so-fancy --debug
Diff-so-fancy: https://github.com/so-fancy/diff-so-fancy
Version      : 1.4.0

Usage:

git diff --color | diff-so-fancy         # Use d-s-f on one diff
cat diff.txt | diff-so-fancy             # Use d-s-f on a diff/patch file
diff -u one.txt two.txt | diff-so-fancy  # Use d-s-f on unified diff output

diff-so-fancy --colors                   # View the commands to set the recommended colors
diff-so-fancy --set-defaults             # Configure git-diff to use diff-so-fancy and suggested colors
diff-so-fancy --patch                    # Use diff-so-fancy in patch mode (interoperable with `git add --patch`)

# Configure git to use d-s-f for *all* diff operations
git config --global core.pager "diff-so-fancy | less --tabs=4 -RFX"

# Configure git to use d-s-f for `git add --patch`
git config --global interactive.diffFilter "diff-so-fancy --patch"

[scottchiefbaker]

Are you sure you have the latest from master? There should definitely be --debug output. That's really weird.

Why don't you try the next branch and see if that fixes your problem?

[scottchiefbaker]

For the record you should see something like this:

bakers@yellow(~/github/diff-so-fancy)
:./diff-so-fancy --debug
Diff-so-fancy   : v1.4.1
Git             : v2.27.0
Perl            : v5.26.3

Terminal width  : 187
Terminal $LANG  : en_US.UTF-8

Supports Unicode: Yes
Unicode Ruler   : Yes

Less Charset Var: LANG
Less Charset    : en_US.UTF-8

Is Windows      : No
Operating System: linux

[felsenhower]

Yep, I'm pretty sure I was on the master branch. but now that I switched to next I can't reproduce the bug anymore, so it could be fixed. But diff-so-fancy --debug still produces nothing like you specified above. So maybe that's a second bug :)

[scottchiefbaker]

Line 57 should call show_debug_info() which is defined at line 935. Do you not have that?

[felsenhower]

Well, I'm not a Perl Pro, but the source looks like you described. However, modifying the source around Line 57 like this

if ($args->{debug}) {
        print "Hey!";
        exit();
}
print($args->{debug});

yields the following:

$ diff-so-fancy --debug                                             
Use of uninitialized value in print at /Users/rfelgenh/.local/bin/diff-so-fancy.d/diff-so-fancy line 60.

So I guess the debug flag is never set. I can also reproduce that on other machines.

[scottchiefbaker]

Well maybe I can dig some more then... what OS are you using, and what version of Perl?

[felsenhower]

Apart from the system mentioned at the very top, Manjaro Linux with perl v5.32.1.

[felsenhower]

I figured out that --debug not working was a fault on my end. The output is now

$ diff-so-fancy --debug
Diff-so-fancy   : v1.4.1
Git             : v2.24.3128
Perl            : v5.18.4

Terminal width  : 150
Use of uninitialized value $ENV{"LANG"} in concatenation (.) or string at /path/to/diff-so-fancy line 946.

Alternatively:

$ LANG=C diff-so-fancy --debug
Diff-so-fancy   : v1.4.1
Git             : v2.24.3128
Perl            : v5.18.4

Terminal width  : 150
Terminal $LANG  : C

Supports Unicode: Yes
Unicode Ruler   : Yes

Less Charset Var: LANG
Less Charset    : C

Is Windows      : No
Operating System: darwin

Looks like the mac is weirdly set up and otherwise everything is okay.

[scottchiefbaker]

I'm not a shell expert, but I think $LANG needs to be set to SOMETHING so the shell knows how to order things, and handle unicode stuff. The issue here is that the lack of a $LANG value of any kind is preventing d-s-f from knowing if your terminal supports UTF-8 or not.

[ericbn]

As far as I've tracked this, the issue was introduced in 75587c6. The function get_less_charset now returns a tuple. But it does return (); (instead of return ("", "");) when no env variables are found, hence making the pattern match my ($less_env_var, $less_charset) = get_less_charset(); fail because the tuple is empty in this case.

I've mentioned I'm fixing this in #398.

[scottchiefbaker]

This should be fixed on the next branch...

61bbdf7 and 9caa68e landed to address this.