SemVer: Update documentation about removing optional dependencies

[ehuss]

This updates the documentation cautioning against removing optional dependencies with more up-to-date information about using the dep: syntax in the features table. This documentation was written before dep:, and I just forgot to update these docs when it was stabilized.

[rustbot]

r? @weihanglo

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[epage]

I think its fine for us to suggest this be treated as minor. The main risk is rust-lang/rust#109005 as people might be seeing the internal names and using them. I actually saw someone mislead by this when demoing the compiler error (the entire serde example was driven by what the compiler said) .

[epage]

r= me when you can

[ehuss]

@bors r=epage

[bors]

📌 Commit 8fe995f has been approved by epage

It is now in the queue for this repository.

[bors]

⌛ Testing commit 8fe995f with merge 952bcab...

[bors]

💔 Test failed - checks-actions

[ehuss]

@bors retry

0xc0000374 (STATUS_HEAP_CORRUPTION) when running rust-lld on x86_64-pc-windows-gnu. I have not seen that before, not sure what is up.

---- custom_target::custom_bin_target stdout ----
running `D:\a\cargo\cargo\target\debug\cargo.exe build --target custom-bin-target.json -v`
thread 'custom_target::custom_bin_target' panicked at tests\testsuite\custom_target.rs:132:57:

test failed running `D:\a\cargo\cargo\target\debug\cargo.exe build --target custom-bin-target.json -v`
error: process exited with code 101 (expected 0)
--- stdout

--- stderr
   Compiling foo v0.0.1 (D:\a\cargo\cargo\target\tmp\cit\t1096\foo)
     Running `rustc --crate-name foo src\main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 -C metadata=f9e88282337cd66d -C extra-filename=-f9e88282337cd66d --out-dir D:\a\cargo\cargo\target\tmp\cit\t1096\foo\target\custom-bin-target\debug\deps --target \\?\D:\a\cargo\cargo\target\tmp\cit\t1096\foo\custom-bin-target.json -L dependency=D:\a\cargo\cargo\target\tmp\cit\t1096\foo\target\custom-bin-target\debug\deps -L dependency=D:\a\cargo\cargo\target\tmp\cit\t1096\foo\target\debug\deps`
error: linking with `rust-lld` failed: exit code: 0xc0000374
  |
  = note: "rust-lld" "-flavor" "gnu" "D:\\a\\cargo\\cargo\\target\\tmp\\cit\\t1096\\foo\\target\\custom-bin-target\\debug\\deps\\foo-f9e88282337cd66d.foo.9076a0c5959399b7-cgu.0.rcgu.o" "--as-needed" "-L" "D:\\a\\cargo\\cargo\\target\\tmp\\cit\\t1096\\foo\\target\\custom-bin-target\\debug\\deps" "-L" "D:\\a\\cargo\\cargo\\target\\tmp\\cit\\t1096\\foo\\target\\debug\\deps" "-L" "C:\\Users\\runneradmin\\.rustup\\toolchains\\nightly-x86_64-pc-windows-gnu\\lib\\rustlib\\custom-bin-target\\lib" "-Bdynamic" "--eh-frame-hdr" "-z" "noexecstack" "-L" "C:\\Users\\runneradmin\\.rustup\\toolchains\\nightly-x86_64-pc-windows-gnu\\lib\\rustlib\\custom-bin-target\\lib" "-o" "D:\\a\\cargo\\cargo\\target\\tmp\\cit\\t1096\\foo\\target\\custom-bin-target\\debug\\deps\\foo-f9e88282337cd66d" "--gc-sections"
  = note: rust-lld: warning: cannot find entry symbol _start; not setting start address
          

error: could not compile `foo` (bin "foo") due to previous error

Caused by:
  process didn't exit successfully: `rustc --crate-name foo src\main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 -C metadata=f9e88282337cd66d -C extra-filename=-f9e88282337cd66d --out-dir D:\a\cargo\cargo\target\tmp\cit\t1096\foo\target\custom-bin-target\debug\deps --target \\?\D:\a\cargo\cargo\target\tmp\cit\t1096\foo\custom-bin-target.json -L dependency=D:\a\cargo\cargo\target\tmp\cit\t1096\foo\target\custom-bin-target\debug\deps -L dependency=D:\a\cargo\cargo\target\tmp\cit\t1096\foo\target\debug\deps` (exit code: 1)

note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    custom_target::custom_bin_target

[bors]

⌛ Testing commit 8fe995f with merge e4de526...

[bors]

☀️ Test successful - checks-actions
Approved by: epage
Pushing e4de526 to master...