Remove rustc-dev-guide submodule

[camelid]

Rationale:

• The submodule hasn't been updated in 10 months (since April 2020)
• It's unlikely that there's a need for it to be a submodule -- people
  can just clone the rust-lang/rustc-dev-guide repo
• Submodules are a pain

See also the discussion on Zulip.

[rust-highfive]

r? @Mark-Simulacrum

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[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

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[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

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configure: rust.channel         := nightly
configure: rust.debug-assertions := True
configure: llvm.assertions      := True
configure: dist.missing-tools   := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
configure: 
---
skip untracked path cpu-usage.csv during rustfmt invocations
skip untracked path src/doc/book/ during rustfmt invocations
skip untracked path src/doc/rust-by-example/ during rustfmt invocations
skip untracked path src/llvm-project/ during rustfmt invocations
Running `"/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt" "--config-path" "/checkout" "--edition" "2018" "--unstable-features" "--skip-children" "--check" "/checkout/src/bootstrap/toolstate.rs"` failed.
Diff in /checkout/src/bootstrap/toolstate.rs at line 85:
 // We do require that we checked whether they build or not on the tools builder,
If you're running `tidy`, try again with `--bless`. Or, if you just want to format code, run `./x.py fmt` instead.
 // though, as otherwise we will be unable to file an issue if they start
 // failing.
-static NIGHTLY_TOOLS: &[(&str, &str)] = &[
-    ("miri", "src/tools/miri"),
-    ("embedded-book", "src/doc/embedded-book"),
-];
+static NIGHTLY_TOOLS: &[(&str, &str)] =
+    &[("miri", "src/tools/miri"), ("embedded-book", "src/doc/embedded-book")];
 
 fn print_error(tool: &str, submodule: &str) {
     eprintln!();
Build completed unsuccessfully in 0:00:23

[Mark-Simulacrum]

Hm, so I actually think we should not do this, but rather get into the habit of bumping the submodule more often and start distributing the dev guide as part of the rustc-docs component (or maybe a new one, given that one has problems with being installed alongside rust-docs). It's annoying that we don't provide an offline copy of it to users today; we should fix that.

That said, I would also not object to approving this in the meantime.

[jyn514]

Is there a point in having it as a submodule if it's only used for release artifacts? Could we change the release process to clone the rustc-dev-guide repo instead?

[Mark-Simulacrum]

Submodules or an equivalent gives you pinning, which is critical if we want reproducible builds and just otherwise ensures that CI keeps passing, including in upstream distros from source tarballs. I would guess we can update it roughly on the same pace as other books; @ehuss updates those from time to time I think.

[camelid]

It's annoying that we don't provide an offline copy of it to users today; we should fix that.

You're right that it might be nice to provide an offline copy in rust-lang/rust rust-docs, but if people want an offline copy they can just clone rust-lang/rustc-dev-guide.

[camelid]

I don't care too much either way about this change; I just think we should only keep the submodule if it is regularly updated. So if @ehuss or someone else is okay with updating this every short while, then I don't think I see any harm in keeping it.

Either way, if we remove it or keep it, we can always easily reverse our decision later.

[Mark-Simulacrum]

@ehuss would it be difficult to update the dev guide alongside the other books? I think you have a script that you run, right?

[ehuss]

Yea, I can add it. I'll be doing an update tomorrow, I'll include an update then.

I'm not sure I agree with the general idea of providing the dev-guide offline, since I've not seen anyone request it, and I suspect nobody even knows it exists (and how would they?). It makes updating submodules slower for everyone (and for people like me, my internet is fairly slow, it can take a significant amount of time). But it doesn't bother me for the bi-weekly updates.

[Mark-Simulacrum]

Hm, well, I recall @nikomatsakis at least has mentioned to me that in pre-COVID times when travel was more of a regular occurrence, he would make extensive use of our std docs on planes and wanted the dev guide in some cases (but didn't have it available as it wasn't packaged). I could be convinced that we shouldn't use a submodule for it though - there's not really a need for rustc developers to get it, it'd be fine for only CI to clone the repository and we can track the commit in rustbuild or something.

[Mark-Simulacrum]

I'll close this in the meantime as it sounds like we're going to start updating the submodule.