Backslash escapes inside math and code are fontified as Markdown markup

[saf-dmitry]

Backslashes inside math and code are fontified as Markdown markup.

Expected Behavior

Backslashes as part of math or code are fontified according to the type of content (i.e., LaTeX or corresponding code language).

Actual Behavior

Backslashes inside math or code are fontified and propertized as Markdown markup:

This is especially misleading when hiding Markdown syntax is enabled.

Steps to Reproduce

See the examples above.

Backtrace

Software Versions

• Markdown Mode: From Git on 2023-05-21
• Emacs: 28.2.1
• OS: macOS 10.15

Note

Commit ae1085a

[jimporter]

I think this would just need to add an extra check to not fontify backslash escapes when fontification has already added one of the following faces to the backslash:

• markdown-inline-code-face
• markdown-pre-face
• markdown-math-face

That should be pretty straightforward with some new markdown-match-escape function that checks the backslash's face before returning whether it matched.

Maybe there's a cleaner way to do that though?

[saf-dmitry]

I think this would just need to add an extra check to not fontify backslash escapes when fontification has already added one of the following faces to the backslash:

• markdown-inline-code-face
• markdown-pre-face
• markdown-math-face

That should be pretty straightforward with some new markdown-match-escape function that checks the backslash's face before returning whether it matched.

Yes, that is how I would approach this. Another point to consider is, it should fontify only backslashes not preceding by another backslashes, i.e., in \\ only the first backslash should be fontified because the second backslash stands for itself. Generally speaking, in something like \\\\\\ only odd, i.e., 1, 3, and 5 backslash positions should be fontified.

[jimporter]

Yes, that is how I would approach this. Another point to consider is, it should fontify only backslashes not preceding by another backslashes, i.e., in \\ only the first backslash should be fontified because the second backslash stands for itself. Generally speaking, in something like \\\\\\ only odd, i.e., 1, 3, and 5 backslash positions should be fontified.

This part should already work. The regexp is (approximately) \\., so it'll match a backslash followed by anything. That means it'll see the first backslash, then skip past the next one before trying again. If you type a bunch of backslashes in a row into a markdown-mode buffer, it should do the right thing.

[jimporter]

@saf-dmitry Ok, hopefully my PR fixes this. Can you try it out to see?

[saf-dmitry]

I just played with it a little bit and it looks good.

The markdown-literal-faces variable can be re-used for various other purposes as well, so I would consider adding the following faces to the list:

• markdown-url-face
• markdown-plain-url-face
• markdown-language-keyword-face
• markdown-language-info-face
• markdown-metadata-key-face
• markdown-metadata-value-face
• markdown-html-entity-face
• markdown-html-tag-name-face
• markdown-html-tag-delimiter-face
• markdown-html-attr-name-face
• markdown-html-attr-value-face

And maybe these faces too:

• markdown-link-title-face
• markdown-reference-face
• markdown-footnote-marker-face
• markdown-line-break-face
• markdown-comment-face

[jimporter]

markdown-link-title-face

Link titles look like they support escape sequences, so I think they should be excluded from markdown-literal-faces. The others make sense though (I think...)

[saf-dmitry]

It seems that the current solution works in code blocks only if native fontification is disabled (which is the default). If the variable markdown-fontify-code-blocks-natively is set to t, the backslash fontification issue comes again:

I think we should reopen the issue.

[jimporter]

It seems that the current solution works in code blocks only if native fontification is disabled (which is the default). If the variable markdown-fontify-code-blocks-natively is set to t, the backslash fontification issue comes again:

@saf-dmitry Thanks for noticing, here's a fix: #836

[saf-dmitry]

Thank you for the prompt fix. It works.