Rollup of 8 pull requests

[Centril]

Successful merges:

• apfloat: improve doc comments #63416 (apfloat: improve doc comments)
• BTreeSet intersection, is_subset & difference optimizations #64820 (BTreeSet intersection, is_subset & difference optimizations)
• syntax: cleanup param, method, and misc parsing #64910 (syntax: cleanup param, method, and misc parsing)
• Remove unneeded fn main blocks from docs #64912 (Remove unneeded fn main blocks from docs)
• Fixes #64919. Suggest fix based on operator precendence. #64933 (Fixes Suggested fix does not account for operator precedence #64919. Suggest fix based on operator precendence.)
• Add lower bound doctests for saturating_{add,sub} signed ints #64943 (Add lower bound doctests for saturating_{add,sub} signed ints)
• Simplify interners #64950 (Simplify interners)
• Don't mark borrows of zero-sized arrays as indirectly mutable #64967 (Don't mark borrows of zero-sized arrays as indirectly mutable)

Failed merges:

r? @ghost

[Centril]

@bors r+ p=8 rollup=never

[bors]

📌 Commit 74586e2 has been approved by Centril

[ecstatic-morse]

@Centril #64967 didn't get blessed .stderr committed, can you back it out for now.

[rust-highfive]

Your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-10-01T21:58:17.3477123Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-10-01T21:58:17.3668977Z ##[command]git config gc.auto 0
2019-10-01T21:58:17.3738111Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-10-01T21:58:17.3801087Z ##[command]git config --get-all http.proxy
2019-10-01T21:58:17.3938063Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/64971/merge:refs/remotes/pull/64971/merge
2019-10-01T21:58:18.1554993Z fatal: couldn't find remote ref refs/pull/64971/merge
2019-10-01T21:58:18.2797771Z ##[warning]Git fetch failed with exit code 128, back off 9.997 seconds before retry.
2019-10-01T21:58:28.1911448Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/64971/merge:refs/remotes/pull/64971/merge
2019-10-01T21:58:28.7876234Z fatal: couldn't find remote ref refs/pull/64971/merge
2019-10-01T21:58:28.8395694Z ##[warning]Git fetch failed with exit code 128, back off 1.705 seconds before retry.
2019-10-01T21:58:30.4971691Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/64971/merge:refs/remotes/pull/64971/merge
2019-10-01T21:58:31.1045922Z fatal: couldn't find remote ref refs/pull/64971/merge
2019-10-01T21:58:31.1555504Z ##[error]Git fetch failed with exit code: 128
2019-10-01T21:58:31.1868969Z ##[section]Starting: Checkout
2019-10-01T21:58:31.1870581Z ==============================================================================
2019-10-01T21:58:31.1870636Z Task         : Get sources
2019-10-01T21:58:31.1870688Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

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