Link to docs.rs environment details from "Build failed" page

[Shnatsel]

My crate auditable is doing something quite weird and fails to build on docs.rs. I needed to detect whether it's being built on docs.rs or not to work around the issue. Turns out it's possible and documented here, but that page is not easily discoverable. If "Build failed" page contained either a link to that page or mentioned the DOCS_RS env variable, such situations would be easier to handle.

[jyn514]

Mentoring instructions: Around

docs.rs/templates/crate/details.html

Lines 148 to 153 in 6b74ba1

	{# Display a warning telling the user we failed to build the docs #}
	<div class="warning">
	docs.rs failed to build {{ details.name }}-{{ details.version }}<br>Please check the
	<a href="/crate/{{ details.name }}/{{ details.version }}/builds">build logs</a> and, if you believe this is
	docs.rs' fault, <a href="https://github.com/rust-lang/docs.rs/issues/new/choose">open an issue</a>.
	</div>

, add a link to /about and a mention of DOCS_RS=1.

[jyn514]

Actually - what if instead we made an FAQ page for failed builds?

Q: How do I detect docs.rs?
A: DOCS_RS=1

Q: I need a dependency that's not installed.
A: crates-build-env

Q: I need internet access.
A: Sorry, but no.

[jyn514]

I guess at that point we should just fix #888

[Kixiron]

Agreed, those would be fitting things for full-on docs. Chapters I've had ideas for are:

• Detect docs.rs in build scripts
• Detect docs.rs in cfg
• Limits
  • Internet access
• Need a dependency
• Badges
• Redirects
• Cargo metadata
• Local testing
• How do I get my crate on docs.rs (I've seen this question many times)