rustdoc: terse diagnostic on malformed intra-doc link (single instead of double colon)

[sanbox-irl]

Problem

I wrote:

[\`TextManager:atlases\`]

but I meant to write TextManager::atlases

The error I got was:

warning: unresolved link to `TextManager:atlases`

But a better error (for my case) would have been referencing that I was missing a semicolon.

Proposed Solution

Since I believe any item cannot have a single : in it, I propose the error should just lint for any illegal characters in a path.

I understand this might be more complex because of partial paths, but I am not familiar enough with those to address them here.

Notes

No response

[weihanglo]

This is a rustdoc issue, let me transfer this for you.

@rustbot transfer rust-lang/rust