syntax: multiple issues in syntax highlighting of TOML files

[sknaumov]

Is there an existing issue for this?

• I have searched the existing issues

Midnight Commander version and build configuration

GNU Midnight Commander 4.8.30
Built with GLib 2.80.0
Built with S-Lang 2.3.3 with terminfo database
Built with libssh2 1.11.0
With builtin Editor and Aspell support
With subshell support as default
With support for background operations
With mouse support on xterm and Linux console
With support for X11 events
With internationalization support
With multiple codepages support
With ext2fs attributes support
Virtual File Systems:
 cpiofs, tarfs, sfs, extfs, ext2undelfs, ftpfs, sftpfs, fish
Data types:
 char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64;

Operating system

Linux sknaumov-ThinkPad-T14-Gen-3 6.8.0-90-generic #91-Ubuntu SMP PREEMPT_DYNAMIC Tue Nov 18 14:14:30 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Is this issue reproducible using the latest version of Midnight Commander?

• I confirm the issue is still reproducible with the latest version of Midnight Commander

How to reproduce

Just open attached TOML file in mcedit.

Expected behavior

I've prepared alternative toml.syntax file.

Exact colors are discussable, but I've tried to unify them with syntax files of similar formats.

Actual behavior

1. Broken comments.
2. Escapes in basic strings are neither highlighted nor properly handled.
3. Literal strings are not highlighted.
4. Multi-line strings are not properly handled.
5. Inconsistent highlighting of inline tables.
6. Sections are hardly distinguished from comments.
7. Colors are not unified with other similar files (YAML, INI).
8. Acid-like look when there are a lot of strings.

Additional context

Is there a chance that this fix will be available in Ubuntu 26.04?

[zyv]

@egmontkob, maybe you could look into this before you merge #5001 - I'm afraid it will be quite some work to rebase after merge. Maybe there are some other open syntax tickets, but nothing comes to mind... other than the very old PRs in the legacy repository:

https://github.com/MidnightCommander/mc-old/pulls

[egmontkob]

I'm not familiar with TOML, nor with mc's syntax highlighting syntax. So I'd prefer to stay out of judging this patch. The screenshots look pretty convincing. If none of us can really judge then I think we can just go ahead and accept it.

I'm happy to rebase either one on top of the other, based on which order the two changes end up landing. It's no big deal at all. Just run the script posted in #5001, and then some boring fiddling with git.

[egmontkob]

Is there a chance that this fix will be available in Ubuntu 26.04?

Unfortunately no, unless you convince Ubuntu downstream to apply it.

[zyv]

I'm not familiar with TOML, nor with mc's syntax highlighting syntax. So I'd prefer to stay out of judging this patch. The screenshots look pretty convincing. If none of us can really judge then I think we can just go ahead and accept it.

I'm familiar with TOML. It’s used in Python project files:

https://github.com/MidnightCommander/website/blob/master/pyproject.toml

The screenshots look like an obvious improvement in as far as it's possible to achieve with the limitations of our editor syntax highlighting engine...

[egmontkob]

I find the dark green a bit hard to read (on the blue background; it's surely different with other skins), maybe there I'd go with brigth green instead. Also, I find bright cyan more readable than dark cyan: maybe swap the two??

But as OP says, some of these might originate from similar syntax highlight files, in which case it's wiser to remain consistent, and maybe one day change them all.

[sknaumov]

I also do not familiar with TOML peculiarities, as I also use it only for pyproject.toml, but I've tried to look at TOML specification to see how corner cases look like.

BTW, it looks like it is better to add . to possible symbols in key:

keyword linestart \[\t\s\]\{0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_-\}\[0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_-.\] key

To handle the following case properly:

[section]
root.middle.leaf = 1

BTW, brightcyan indeed could be used for bool/number and it will be consistent with .ini files. I just preferred cyan to make braces standout. As to strings, YAML uses dark color for them, as well as C/Shell and so on + it makes it possible to use brightgreen for escapes.

[sknaumov]

@egmontkob, maybe you could look into this before you merge #5001

@zyv I've just added another issue #5003 - for Kconfig syntax highlighting that I prepared just yesterday.

[zyv]

@sknaumov Could you please submit a PR, possibly one for both syntaxes? One commit per syntax file addition, please.