Upgrade toolchain to Rust-1.86

[jsai28]

Which issue does this PR close?

Closes #15619.

Rationale for this change

Improve build times.

What changes are included in this PR?

Updating toolchain to Rust 1.86 and fixing associated errors and warnings.

The main changes were doc indentation updates and changing repeat to use repeat_n. There are few other changes such as using .ok() instead of manually implementing it, using is_empty() instead of checking if length is 0, and others similar to this.

Are these changes tested?

Are there any user-facing changes?

[DerGut]

I verified the clippy warnings I am getting locally and they match exactly 👍

---

Interestingly, when I run clippy on the datafusion/physical-optimizer crate:

cargo clippy --manifest-path datafusion/physical-optimizer/Cargo.toml

I get a warning.

warning: parameter is only used in recursion
  --> datafusion/physical-optimizer/src/aggregate_statistics.rs:48:9
   |
48 |         config: &ConfigOptions,
   |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_config`
   |
note: parameter used here
  --> datafusion/physical-optimizer/src/aggregate_statistics.rs:86:42
   |
86 |                     self.optimize(child, config).map(Transformed::yes)
   |                                          ^^^^^^
...
91 |             plan.map_children(|child| self.optimize(child, config).map(Transformed::yes))
   |                                                            ^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#only_used_in_recursion
   = note: `#[warn(clippy::only_used_in_recursion)]` on by default

This warning also shows up with v1.85.0 so it shouldn't be relevant for this PR.

[alamb]

Thanks @DerGut

Interestingly, when I run clippy on the datafusion/physical-optimizer crate:

I actually found it fails for me on rust 1.85 as well:

(venv) andrewlamb@Andrews-MacBook-Pro-2:~/Software/datafusion$ cargo clippy -p datafusion-physical-optimizer
warning: parameter is only used in recursion
  --> datafusion/physical-optimizer/src/aggregate_statistics.rs:48:9
   |
48 |         config: &ConfigOptions,
   |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_config`
   |
note: parameter used here
  --> datafusion/physical-optimizer/src/aggregate_statistics.rs:86:42
   |
86 |                     self.optimize(child, config).map(Transformed::yes)
   |                                          ^^^^^^
...
91 |             plan.map_children(|child| self.optimize(child, config).map(Transformed::yes))
   |                                                            ^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#only_used_in_recursion
   = note: `#[warn(clippy::only_used_in_recursion)]` on by default

warning: `datafusion-physical-optimizer` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s
(venv) andrewlamb@Andrews-MacBook-Pro-2:~/Software/datafusion$

Any chance you could make a follow PR to fix this?

[alamb]

Thank you @jsai28 -- this looks great. Much appreciated

[alamb]

Since this is non controversial let's upgrade and see how it works

FYI @logan-keede -- maybe we can see how much this helps the build speed

[DerGut]

Yes, I can take a look at the only used in recursion warning 👍