Change:
Following , we realized that rustdoc users would prefer to have a syntax extension rather than using plain HTML to have warning blocks. suggested the following: suggested: What do you think? cc
Personal Opinions: The first style will look fine for short forms, but I'm not sure for longer text. A possible syntax: Which to me pushes the text too far right. Not having any spacing, but just separating with newlines, seems hard to parse at a glance what is part of the WARNING, and prevents multiple line breaks inside the warning. Also, it's not as extensible. INFO can be , but if we ever want more extensions, they would increasingly possibly conflict with other things. The second style makes it immediately clear what is part of the block, and is unlikely to accidentally conflict if we ever want to add more block styles. It also supports multiple lines or inner blocks trivially. A final advantage is that it may support nested blocks, in case those ever come to be useful. Overall: I prefer the second form, both aesthetically and for future-proofing
I think I agree with in preferring the second form. I like the first form's simplicity, but it also seems surprising that is treated as a 'keyword' and will change the formatting of the docs.
That's why we have this debate. :stuckouttongue:
I personally actually prefer stabilizing a CSS class, I think we should do more of that, just because parsing can get annoying. But this is not that hard to parse anyway. The problem with is precisely that you can't scope it easily: what if you want to add code blocks? bullet points?
The problem with this is it ties rustdoc to the HTML backend; like I said nothing rustdoc currently does guarentees that it will generate HTML from the markdown. Changing that means that to make the JSON backend have the same info, we'd have to add a full HTML parser to rustdoc just to read the HTML in the markdown, because pulldown does not parse HTML for us. I really think we should avoid making the JSON backend a second-class citizen.
Also there's not much point to this if it's just a little CSS IMO, you can add that yourself with and it will look just as good and be more flexible since you can control the styles yourself.
I'm not a giant fan of the syntax because it looks odd when rendered by anything other than rustdoc, which I'd rather avoid, one of the major design concerns for intra-doc links was compatibility with other markdown parsers:
So, I agree, but I'm not convinced that the warning class is something that needs to be surfaced in the JSON backend as anything special. Also, bear in mind, HTML is a part of markdown: valid HTML (well a subset of HTML) is valid markdown. Users already can , and they do that in many cases. Markdown parsers already need to be able to handle HTML. There's nothing new there. Whatever consumes the JSON backend will need to be able to handle that too. I mean, yes, in theory, in practice people don't do this because of the barrier to entry (you have to get your tools to use that, including )
Also, this is incorrect, pulldown absolutely parses HTML. It has to, like I said valid HTML is valid Markdown. It doesn't parse it thoroughly, I believe you can mess it up with sufficiently complex HTML, but it parses HTML. What this changes is subtler: up till now you did not need any particular stylesheet to acceptably render rustdoc markdown from the JSON backend on your own (just use your favorite markdown renderer's stylesheet), but now you will need other css classes to handle rendering warnings as warnings.
I do not agree that this is a problem. I've used Phabricator's implementation of this approach happily and it is by design that warning banners are one paragraph. It is not the intention that you would put entire sections of documentation into a warning banner. They are for a brief callout. It's fine to refer to a subsequent section of the documentation from the callout if needed. I suppose this is a matter of taste but it's one where I believe the opinionatedness of the syntax is a positive thing.
So I discussed this a bit with on the side, we agree that the effect on the JSON backend isn't major since HTML is already a subset of markdown and docs use HTML already (especially for images and tables). My position is as follows: I strictly prefer HTML over some other scoped syntax with nuances people have to learn. I don't think there's as much value in unscoped syntax which makes my position "HTML or nothing", basically. I'm not wholly against unscoped single-line syntax. We and syntax in W3C specs and you invariably need to add more stuff to it (there's an HTML class in these specs for this reason). Furthermore, Rust has a strong culture of wrapping text, so this means we need to work well while wrapped, and that means we're again introducing some form of scoping mechanism (e.g. indenting the text), which editors will have to learn, as well.
I don't know about admonitions specifically but there seems to be something of a community habit to use "magic tags" on fenced code blocks for this sort of features (e.g. github has a tag), maybe that could be an option? I don't know if pulldown_cmark has a hook for manipulating code blocks but… So a warning would be or maybe the tag would be to leave room for things like note/todo/danger/… Alternatively, take a gander at how other markdown implementations extend the language for this sort of features? e.g. seems to be using for admonitions.
Hmm, but is still for code, even if it has some extra behavior. Aside from the design concerns, this would be feasible to implement: we just extract the language string from the code block with pulldown.
Could you use something that's already built into markdown? For example, rustdoc could take and render it as an admonition.
That's what suggested: to use markdown and make some changes on rustdoc side. I think the codeblock approach is the best personally.
My bad, I didn't see that.
I wonder if it makes more sense to add this as a proc-macro. Rustdoc can still provide the CSS classes and things, and you could use them with HTML directly, but you could use or something and it would expand to the correct HTML tags and classes.
Might be better to have a then, no?
Is that going to be a special header similar to the "unsafe"/"experimental"/etc ones, or is that going to also be used within docs in an order-sensitive way? If the latter we should probably just use a CSS class; mixing and is ugly
Agreed. Among the suggested ideas, my favourite one remains the code block with "warning" as tag:
Yeah, but triple backticks is also for preformatted text without further markup, so you won't be able to e.g. use text formatting (or other code) in there
True... Finding the right syntax is much more complicated than expected...
That's the issue of using markdown, for all that it has a pretty nice baseline syntax it really was not designed for extensibility.
We can always use : it'd allow to have text formatting inside it.
I would use , it's not quite kosher to invent arbitrary HTML tags (though you can use Custom Elements, which is more heavyweight)
Sounds good to me. It's funny because we kinda came back to the . :rofl:
I just thought: we could use tag in the markdown and then transform it into in the generated HTML?
My main objection to all of these is that rustdoc shouldn't be adding custom markdown syntax that no one else supports. Any new syntax we use should look reasonable even if rendered with the default renderer.
Well, it remains valid markdown since it's HTML (even though it's custom tag). I'm completely fine with , but it might be simpler/better for users to simply write .
Coming back to this (because of ), it seems like the conversation kinda agreed on adding a CSS class directly and then it would look like this in the docs: . I'll send a PR in the next days and then we can open an FCP to see if everyone is ok with it (and if not, we'll have code to help the debate).
This indeed seems like a better solution than the HTML block. It also plays better with something said about not linking it too much too HTML. This will look like a proper warning or note, mostly independent of the HTML generation.
They also seemed to not be too favourable to anything that needs some extra parsing from rustdoc iuc. I'm fine with bot the github solution and the CSS class.
Maybe one more comment to make here. The note-taking app, which uses Markdown also has a similar syntax to create these blocks. It is called . It uses a syntax similar to the syntax that is used for doc intra-links currently, and it is fully compatible with them. I am uncertain if this is any better than what suggested from the GitHub syntax, but because of the similarity to the doc intra-link syntax. I do feel like this might be interesting because it should go well with backwards compatibility. However, this may look worse than the GitHub syntax solution when not going through cargo doc.
I thought I'd already left this comment, but I'd really like to avoid adding more markdown syntax where possible. This feature works fine without special syntax, I don't think we need it. edit: copying over the reasoning from the :
Although, I might not agree fully, I can fully appreciate and understand the reasoning you left in the corresponding PR. Still, I do think it might be worth to standardize some kind of syntax for some kind of warning block. This does not actually require customized markdown. Alternatively, I can suggest adding the GitHub flavor with emojis to the . This may help in standardizing short form warnings and notes within documentation. We could for example propose to standardize: which should look like the following I do value people's opinion on this. Is this a possible compromise?
That's a valid alternative, I think the yellow color is pretty important though, and it's useful for themes to be able to make styling decisions about warnings so I do think that having some way of marking it is important. I just don't think the way of marking it should be some magic invocation as opposed to CSS classes. (And I think that the bar for a feature that is adding new semantics to the Rustdoc markdown parser is much, much higher than that of one stabilizing a CSS class)
100% agree. I will look at the Rust API guidelines issue and possibly an RFC to rust to track the adoption in GitHub and possibly eventually merge. Thank you :smile:
Beyond all this discussion of third-party tools, I'd really like to make sure that whatever new syntax and presentation we add to rustdoc can also be to [mdBook]. That way, when the standard library starts using callouts, we can make sure the same style also gets used in The Book. Mostly, The Book seems to just use blockquotes, often with headings like [this one about ownership]. mdBook doesn't do anything special with it: it's [just a block quote with a header]. [mdBook]: [this one about ownership]: [just a block quote with a header]:
This is a good point. Once we have something merged here, I'll send a PR there to have an equivalent.
CC
I'd be happy to add some CSS rules to mdbook if that is what you are proposing.
Yeah, it is.
FYI, using a is not semantic and Microsoft GitHub is setting a bad precedence. — CommonMark Spec v0.30, denotes a in Markdown and is rendered as such. — W3C HTML spec, Unless you are quoting a source, this is not the correct element to use. While I disagree with even using altogether, at least some tools out there are at least translating the blockquote in admonition context into a (div has no semantic meaning which is unfortunately the best HTML option for admonitions). It would be ill-advised to follow Microsoft GitHub’s Markdown syntax fork&mdash;especially with their disregard for semantics. Similarly using a block would also be breaking semantics as an admonition is not preformatted text. CommonMark does have that could be used if the solution was preferred. There’s also other reasonable options noted here that don’t break semantics.
I agree that block quotes for callouts are bad, and would like to work with mdBook to roll out a common syntax (probably ) that will replace the ad-hoc, unsemantic markup that they use right now.
Using is what we agreed upon in The debate now is on the look itself.
Unfortunately isn't great because markdown has a "boundary" when HTML tags are used. I wanted to add a warning indicating that users probably wanted another trait, but intra-doc links don't work (which is the correct behavior per markdown spec).
Works perfectly fine though (well, minus the UI bug I just discovered haha): ! I used this code: I'll send a PR to improve documentation.
Ah. Well I suppose the issue wasn't with intra-doc links, but with inline code blocks. What I tried was that but with bar`, and it failed.
Works too: !
I opened which adds extra explanation on how to use markdown inside html tags. That should solve your issue.
That note is exactly what I was just looking in to. I had it inline, given my familiarity with HTML. TIL that matters.
It doesn't hurt to have it and if it can helps users, well, why not doing it. :)

Discussion:
So, no need to manually enter those Unicode characters! <ins> ### Adding a warning block If you want to make a warning or similar note stand out in the documentation, you can wrap it like this: ```md /// documentation /// /// <div class="warning">A big warning!</div> /// /// more documentation ``` </ins> [`backtrace`]: https://docs.rs/backtrace/0.3.50/backtrace/ [commonmark markdown specification]: https://commonmark.org/ [commonmark quick reference]: https://commonmark.org/help/

margin-bottom: .625em; } <del> p { </del> <ins> p, .docblock > .warning { </ins> /* Paragraph spacing at least 1.5 times line spacing per Web Content Accessibility Guidelines. Line-height is 1.5rem, so line spacing is .5rem; .75em is 1.5 times that. https://www.w3.org/WAI/WCAG21/Understanding/visual-presentation.html */

} /* For the last child of a div, the margin will be taken care of by the margin-top of the next item. */ <del> p:last-child { </del> <ins> p:last-child, .docblock > .warning:last-child { </ins> margin: 0; }

} .example-wrap.ignore .tooltip { <del> color:  var(--codeblock-ignore-color); </del> <ins> color: var(--codeblock-ignore-color); </ins> } .example-wrap.compile_fail:hover .tooltip,

font-size: 1.25rem; } <ins> /* This class only exists for users who want to draw attention to a particular element in their documentation. */ .content .docblock .warning { border-left: 2px solid var(--warning-border-color); padding: 14px; position: relative; /* The "!important" part is required because the rule is otherwise overruled in this CSS selector: ".docblock > :not(.more-examples-toggle):not(.example-wrap)" */ overflow-x: visible !important; } .content .docblock .warning::before { color: var(--warning-border-color); content: "ⓘ"; position: absolute; left: -25px; top: 5px; font-weight: bold; font-size: 1.25rem; } </ins> a.test-arrow { visibility: hidden; position: absolute;

--codeblock-error-color: rgba(255, 0, 0, .5); --codeblock-ignore-hover-color: rgb(255, 142, 0); --codeblock-ignore-color: rgba(255, 142, 0, .6); <ins> --warning-border-color: rgb(255, 142, 0); </ins> --type-link-color: #ffa0a5; --trait-link-color: #39afd7; --assoc-item-link-color: #39afd7;

--codeblock-error-color: rgba(255, 0, 0, .5); --codeblock-ignore-hover-color: rgb(255, 142, 0); --codeblock-ignore-color: rgba(255, 142, 0, .6); <ins> --warning-border-color: rgb(255, 142, 0); </ins> --type-link-color: #2dbfb8; --trait-link-color: #b78cf2; --assoc-item-link-color: #d2991d;

--codeblock-error-color: rgba(255, 0, 0, .5); --codeblock-ignore-hover-color: rgb(255, 142, 0); --codeblock-ignore-color: rgba(255, 142, 0, .6); <ins> --warning-border-color: rgb(255, 142, 0); </ins> --type-link-color: #ad378a; --trait-link-color: #6e4fc9; --assoc-item-link-color: #3873ad;

pub fn must_use(&self) -> bool { true } <ins> /// hello /// /// <div id="doc-warning-1" class="warning">this is a warning</div> /// /// done pub fn warning1() {} /// Checking there is no bottom margin if "warning" is the last element. /// /// <div id="doc-warning-2" class="warning">this is a warning</div> pub fn warning2() {} </ins> } impl AsRef<str> for Foo {

<ins> // Test to check that the "warning blocks" are displayed as expected. go-to: "file://" + |DOC_PATH| + "/test_docs/struct.Foo.html" show-text: true define-function: ( "check-warning", (theme, color, border_color, background_color), block { set-local-storage: {"rustdoc-theme": |theme|, "rustdoc-use-system-theme": "false"} reload: // The IDs are added directly into the DOM to make writing this test easier. assert-css: ("#doc-warning-1", { "margin-bottom": "12px", "color": |color|, "border-left": "2px solid " + |border_color|, "background-color": |background_color|, }) assert-css: ("#doc-warning-2", { "margin-bottom": "0px", "color": |color|, "border-left": "2px solid " + |border_color|, "background-color": |background_color|, }) }, ) call-function: ("check-warning", { "theme": "ayu", "color": "rgb(197, 197, 197)", "border_color": "rgb(255, 142, 0)", "background_color": "rgba(0, 0, 0, 0)", }) call-function: ("check-warning", { "theme": "dark", "color": "rgb(221, 221, 221)", "border_color": "rgb(255, 142, 0)", "background_color": "rgba(0, 0, 0, 0)", }) call-function: ("check-warning", { "theme": "light", "color": "rgb(0, 0, 0)", "border_color": "rgb(255, 142, 0)", "background_color": "rgba(0, 0, 0, 0)", }) </ins>