Fails trom time to time with:
```
info: installing component 'rustc'
memory allocation of 16777216 bytes failed
Error: The process 'C:\Rust\.cargo\bin\rustup.exe' failed with exit code 3221226505
```
on Build (windows-latest, i686-pc-windows-gnu, feat_os_windows)
Add some abstractions to simplify the `rbuf_but_last_n_lines()`
function, which implements the "take all but the last `n` lines"
functionality of the `head` program. This commit adds
- `RingBuffer`, a fixed-size ring buffer,
- `ZLines`, an iterator over zero-terminated "lines",
- `TakeAllBut`, an iterator over all but the last `n` elements of an
iterator.
These three together make the implementation of
`rbuf_but_last_n_lines()` concise.
Fails from time to time with
```
---- test_numfmt::test_should_calculate_implicit_padding_per_free_argument stdout ----
current_directory_resolved:
run: /target/x86_64-unknown-linux-musl/debug/coreutils numfmt --from=auto 1Ki 2K
thread 'test_numfmt::test_should_calculate_implicit_padding_per_free_argument' panicked at 'failed to write to stdin of child: Broken pipe (os error 32)', tests/common/util.rs:859:21
```
`sort` supports three ways to specify the sort mode: a long option
(e.g. --numeric-sort), a short option (e.g. -n) and the sort flag
(e.g. --sort=numeric).
This adds support for the sort flag.
Additionally, sort modes now conflict, which means that an error is
shown when multiple modes are passed, instead of silently picking a mode.
For consistency, I added the `random` sort mode to the `SortMode` enum,
instead of it being a bool flag.
Change the behavior of `wc` to print the counts for a file as soon as
it is computed, instead of waiting to compute the counts for all files
before writing any output to `stdout`. The new behavior matches the
behavior of GNU `wc`.
The old behavior looked like this (the word "hello" is entered on
`stdin`):
$ wc emptyfile.txt -
hello
0 0 0 emptyfile.txt
1 1 6
1 1 6 total
The new behavior looks like this:
$ wc emptyfile.txt -
0 0 0 emptyfile.txt
hello
1 1 6
1 1 6 total
Change the behavior of `uucore::fs::canonicalize()` when `can_mode` is
`CanonicalizeMode::None` so that it does not attempt to resolve the
final component if it is a symbolic link. This matches the behavior of
the function for the non-final components of a path when `can_mode` is
`None`.
Instead of overflowing when calculating the buffer size, use
saturating_{pow, mul}.
When failing to parse the buffer size, we now crash instead of silently
ignoring the error.
To make this work we make default sort a special case of external sort.
External sorting uses auxiliary files for intermediate chunks. However,
when we can keep our intermediate chunks in memory, we don't write them
to the file system at all. Only when we notice that we can't keep them
in memory they are written to the disk.
Additionally, we don't allocate buffers with the capacity of their
maximum size anymore. Instead, they start with a capacity of 8kb and are
grown only when needed.
This makes sorting smaller files about as fast as it was before
(I'm seeing a regression of ~3%), and allows us to seamlessly continue
with auxiliary files when needed.
