Can't run `mdbook build` locally without installing or disabling linkcheck

[Zalathar]

As of #2103:

$ mdbook build --open
2024-12-30 11:30:43 [INFO] (mdbook::book): Book building has started
2024-12-30 11:30:43 [INFO] (mdbook::book): Running the html backend
2024-12-30 11:30:44 [INFO] (mdbook::book): Running the linkcheck backend
2024-12-30 11:30:44 [INFO] (mdbook::renderer): Invoking the "linkcheck" renderer
Checking files changed in master...: 
exec mdbook-linkcheck2 -f 
/Users/stuart/Dev/rust/dev-guide/ci/linkcheck.sh: line 47: exec: mdbook-linkcheck2: not found
2024-12-30 11:30:44 [WARN] (mdbook::renderer): Error writing the RenderContext to the backend, Broken pipe (os error 32)
2024-12-30 11:30:44 [ERROR] (mdbook::renderer): Renderer exited with non-zero return code.
2024-12-30 11:30:44 [ERROR] (mdbook::utils): Error: Rendering failed
2024-12-30 11:30:44 [ERROR] (mdbook::utils): 	Caused By: The "linkcheck" renderer failed

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Building the book now fails if mdbook-linkcheck2 has not been manually installed, even if the contributor doesn't care about linkcheck and just wants to build the book to preview their changes.

And while there is a workaround available, it isn't mentioned by the error message at all.

---

As a temporary workaround, this works:

$ SKIP_LINKCHECK=1 mdbook build

[camelid]

Do you have mdbook-linkcheck2 installed? That's what the error seems to suggest the issue is.

[Zalathar]

I've never manually installed it, so presumably it isn't installed.

[camelid]

We've switched to a different version so you'll have to install it. Feel free to reopen if I misunderstood the issue. :)

[Zalathar]

Well, the issue is that I can no longer build the book without either manually installing linkcheck, or manually disabling linkcheck. But I don't care about linkcheck; I just want to build the book to preview my changes. So the workflow for doing that has become more complicated.

At the very least, it would be nice to have an error message that indicates how to disable linkcheck.

[camelid]

Fair enough. I've opened a PR to make it opt-in instead. #2180