Fix intersperse_fold

[tesuji]

Here is a standalone playground link in case anybody wants to modify code: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=626b4d044fb74f044a36098ad907e40f

Fixes #81145

cc #79479 @jonas-schievink

[rust-highfive]

r? @shepmaster

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[rust-log-analyzer]

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

Click to see the possible cause of the failure (guessed by this bot)

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: 
---
Checking which error codes lack tests...
Found 435 error codes
Found 0 error codes with no tests
Done!
tidy error: `/checkout/library/core/src/iter/adapters/intersperse/tests.rs:3` contains `#[test]`; core unit tests and benchmarks must be placed into `core/tests` or `core/benches`
some tidy checks failed

command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "/checkout/obj/build"
expected success, got: exit code: 1

[tesuji]

The second commit 72dd5a445a3c6663399c86cd33235b5f9e6bd099 is the result of
./x.py fmt run locally. I expected CI catches fmt error. Does something go wrong ? cc @Mark-Simulacrum

[rust-log-analyzer]

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

Click to see the possible cause of the failure (guessed by this bot)

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: 
---
    Checking rand v0.7.3
    Checking alloc v0.0.0 (/checkout/library/alloc)
    Checking std v0.0.0 (/checkout/library/std)
    Checking core v0.0.0 (/checkout/library/core)
error[E0624]: associated function `new` is private
     |
     |
3567 |     let v = Intersperse::new(1..4, 9).fold(Vec::new(), |mut acc, x| {
     |                          ^^^ private associated function

error[E0624]: associated function `new` is private
     |
     |
3573 |     let mut iter = Intersperse::new(1..4, 9);
     |                                 ^^^ private associated function
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0624`.
error: could not compile `core`
error: could not compile `core`

To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
error: build failed
command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "check" "--target" "i686-pc-windows-gnu" "-Zbinary-dep-depinfo" "-j" "16" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace compiler-builtins-c" "--manifest-path" "/checkout/library/test/Cargo.toml" "--all-targets" "-p" "test" "-p" "term" "-p" "std" "-p" "alloc" "-p" "unwind" "-p" "core" "-p" "panic_unwind" "-p" "proc_macro" "-p" "panic_abort" "--message-format" "json-render-diagnostics"
failed to run: /checkout/obj/build/bootstrap/debug/bootstrap check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu --all-targets
Build completed unsuccessfully in 0:00:44

[Mark-Simulacrum]

It looks like your local branch is using the wrong rustfmt for some reason, not sure why that would be though. Please file an issue if you can't successfully drop it from this PR so that I can investigate.

[nagisa]

Can you add a test with a string, such as reported in the original issue? They said that collecting into a vector did work regardless, but not when it was collected into a string.

[tesuji]

Here is the playground link of such test: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=26f37fc7f7fa317f3d458623d047952b

Will add that test soon though I feel the test redundant.

[lukaslueg]

cc @camelid
I'm unsure if the fix is correct with respect to the comment which this PR also removes.

[m-ou-se]

Thanks!

@bors r+

[bors]

📌 Commit 9272d53 has been approved by m-ou-se

[bors]

⌛ Testing commit 9272d53 with merge 202720b...

[bors]

☀️ Test successful - checks-actions
Approved by: m-ou-se
Pushing 202720b to master...