rustup update doesn't find latest nightly if today's is not available

[DarkKirb]

Problem
rustup update does not find the latest nightly if the current one is not available.

when i run rustup update this happens:

info: syncing channel updates for 'stable-x86_64-apple-darwin'
info: syncing channel updates for 'nightly-x86_64-apple-darwin'
info: checking for self-updates

   stable-x86_64-apple-darwin unchanged - rustc 1.38.0 (625451e37 2019-09-23)
  nightly-x86_64-apple-darwin unchanged - rustc 1.40.0-nightly (7979016af 2019-10-20)

I expect rustup to find the 2019-10-21 nightly, which exists according to the component history page.

Steps

1. have a rustup managed nightly toolchain older than 2019-10-21
2. run rustup update when the most recent nightly is not available
3. rustup does not update to 2019-10-21

Potential Cause
Regression from #2002

Notes

Output of rustup --version:

rustup 1.20.2 (13979c968 2019-10-16)

Output of rustup show:

Default host: x86_64-apple-darwin
rustup home:  /Users/charlotted/.rustup

installed toolchains
--------------------

stable-x86_64-apple-darwin
nightly-2019-06-22-x86_64-apple-darwin
nightly-x86_64-apple-darwin (default)

installed targets for active toolchain
--------------------------------------

aarch64-unknown-linux-musl
arm-unknown-linux-musleabihf
i686-pc-windows-gnu
i686-unknown-linux-musl
wasm32-unknown-unknown
x86_64-apple-darwin
x86_64-pc-windows-gnu
x86_64-unknown-linux-musl

active toolchain
----------------

nightly-x86_64-apple-darwin (default)
rustc 1.40.0-nightly (7979016af 2019-10-20)

[Erk-]

I just tried to update as well and it seems to be selecting the 2019-10-20 nightly for me as well.

❯ rustup update
info: syncing channel updates for 'stable-x86_64-unknown-linux-gnu'
info: syncing channel updates for 'beta-x86_64-unknown-linux-gnu'
info: latest update on 2019-10-16, rust version 1.39.0-beta.6 (224f0bc90 2019-10-15)
info: downloading component 'rustc'
 65.8 MiB /  65.8 MiB (100 %)   8.8 MiB/s in  7s ETA:  0s
info: downloading component 'rust-std'
176.1 MiB / 176.1 MiB (100 %)   8.9 MiB/s in 20s ETA:  0s
info: downloading component 'cargo'
info: downloading component 'rust-docs'
 11.8 MiB /  11.8 MiB (100 %)  10.4 MiB/s in  1s ETA:  0s
info: downloading component 'rustfmt'
info: removing previous version of component 'rustc'
info: removing previous version of component 'rust-std'
info: removing previous version of component 'cargo'
info: removing previous version of component 'rust-docs'
info: removing previous version of component 'rustfmt'
info: installing component 'rustc'
 65.8 MiB /  65.8 MiB (100 %)  13.8 MiB/s in  4s ETA:  0s
info: installing component 'rust-std'
176.1 MiB / 176.1 MiB (100 %)  29.2 MiB/s in  6s ETA:  0s
info: installing component 'cargo'
info: installing component 'rust-docs'
 11.8 MiB /  11.8 MiB (100 %)   8.6 MiB/s in  1s ETA:  0s
info: installing component 'rustfmt'
info: syncing channel updates for 'nightly-x86_64-unknown-linux-gnu'
info: latest update on 2019-10-21, rust version 1.40.0-nightly (7979016af 2019-10-20)
info: downloading component 'clippy'
info: downloading component 'rustfmt'
info: downloading component 'rustc'
 66.5 MiB /  66.5 MiB (100 %)   9.4 MiB/s in  7s ETA:  0s
info: downloading component 'rust-std'
180.2 MiB / 180.2 MiB (100 %)   8.5 MiB/s in 21s ETA:  0s
info: downloading component 'cargo'
info: downloading component 'rust-docs'
 11.8 MiB /  11.8 MiB (100 %)   8.5 MiB/s in  1s ETA:  0s
info: downloading component 'rust-src'
info: removing previous version of component 'clippy'
info: removing previous version of component 'rustfmt'
info: removing previous version of component 'rustc'
info: removing previous version of component 'rust-std'
info: removing previous version of component 'cargo'
info: removing previous version of component 'rust-docs'
info: removing previous version of component 'rust-src'
info: installing component 'clippy'
info: installing component 'rustfmt'
info: installing component 'rustc'
 66.5 MiB /  66.5 MiB (100 %)  13.7 MiB/s in  5s ETA:  0s
info: installing component 'rust-std'
180.2 MiB / 180.2 MiB (100 %)  29.3 MiB/s in  6s ETA:  0s
info: installing component 'cargo'
info: installing component 'rust-docs'
 11.8 MiB /  11.8 MiB (100 %)  10.1 MiB/s in  1s ETA:  0s
info: installing component 'rust-src'
info: checking for self-updates
info: downloading self-update

  stable-x86_64-unknown-linux-gnu unchanged - rustc 1.38.0 (625451e37 2019-09-23)
      beta-x86_64-unknown-linux-gnu updated - rustc 1.39.0-beta.6 (224f0bc90 2019-10-15)
   nightly-x86_64-unknown-linux-gnu updated - rustc 1.40.0-nightly (7979016af 2019-10-20)


~ took 1m40s
❯ rustup update
info: syncing channel updates for 'stable-x86_64-unknown-linux-gnu'
info: syncing channel updates for 'beta-x86_64-unknown-linux-gnu'
info: syncing channel updates for 'nightly-x86_64-unknown-linux-gnu'
info: checking for self-updates

   stable-x86_64-unknown-linux-gnu unchanged - rustc 1.38.0 (625451e37 2019-09-23)
     beta-x86_64-unknown-linux-gnu unchanged - rustc 1.39.0-beta.6 (224f0bc90 2019-10-15)
  nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.40.0-nightly (7979016af 2019-10-20)

[DarkKirb]

i just tried to install the nightly manually and rustup is picking up the correct nightly. It's just that the nightly is not labelled correctly.

% rustup install nightly-2019-10-21
info: syncing channel updates for 'nightly-2019-10-21-x86_64-apple-darwin'
info: latest update on 2019-10-21, rust version 1.40.0-nightly (7979016af 2019-10-20)
info: downloading component 'cargo'
info: downloading component 'clippy'
info: downloading component 'rust-docs'
 11.8 MiB /  11.8 MiB (100 %)   5.0 MiB/s in  2s ETA:  0s
info: downloading component 'rust-std'
177.6 MiB / 177.6 MiB (100 %)   6.0 MiB/s in 28s ETA:  0s
info: downloading component 'rustc'
 60.6 MiB /  60.6 MiB (100 %)   6.3 MiB/s in  9s ETA:  0s
info: downloading component 'rustfmt'
info: installing component 'cargo'
info: installing component 'clippy'
info: installing component 'rust-docs'
 11.8 MiB /  11.8 MiB (100 %)   6.7 MiB/s in  1s ETA:  0s
info: installing component 'rust-std'
177.6 MiB / 177.6 MiB (100 %)  32.3 MiB/s in  6s ETA:  0s
info: installing component 'rustc'
 60.6 MiB /  60.6 MiB (100 %)  14.6 MiB/s in  4s ETA:  0s
info: installing component 'rustfmt'

  nightly-2019-10-21-x86_64-apple-darwin installed - rustc 1.40.0-nightly (7979016af 2019-10-20)

[kinnison]

For your future reference: because of when nightly builds begin, and when they finish, the compiler's date and the channel date will almost always differ by 1 day.