Rollup of 7 pull requests

[henryboisdequin]

Successful merges:

• Let io::copy reuse BufWriter buffers #78641 (Let io::copy reuse BufWriter buffers)
• Add error message for private fn #79291 (Add error message for private fn)
• Bump rustfmt version #80843 (Bump rustfmt version)
• Improve rustc_mir_build::matches docs #81364 (Improve rustc_mir_build::matches docs)
• Move some tests to more reasonable directories - 3 #81387 (Move some tests to more reasonable directories - 3)
• Rename NLL* to Nll* accordingly to C-CASE #81463 (Rename NLL* to Nll* accordingly to C-CASE)
• Fix invalid camel case suggestion involving unicode idents #81529 (Fix invalid camel case suggestion involving unicode idents)

Failed merges:

r? @ghost
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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: 
---
skip untracked path cpu-usage.csv during rustfmt invocations
skip untracked path src/doc/book/ during rustfmt invocations
skip untracked path src/doc/rust-by-example/ during rustfmt invocations
skip untracked path src/llvm-project/ during rustfmt invocations
Running `"/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt" "--config-path" "/checkout" "--edition" "2018" "--unstable-features" "--skip-children" "--check" "/checkout/compiler/rustc_mir_build/src/build/expr/into.rs"` failed.
Diff in /checkout/compiler/rustc_mir_build/src/build/expr/into.rs at line 319:
                                         .field(n, ty)
If you're running `tidy`, try again with `--bless`. Or, if you just want to format code, run `./x.py fmt` instead.
                                         .into_place(this.hir.tcx(), this.hir.typeck_results()),
-                            },
+                            }
                         })
                         .collect()