Enhancement of new `fill` command (#7846) to handle content including
ANSI escape codes for formatting or multi-code-point Unicode grapheme
clusters.
In both of these cases, the content is (many) bytes longer than its
visible length, and `fill` was counting the extra bytes so not adding
enough fill characters.
# Description
This script:
```rust
# the teacher emoji `\u{1F9D1}\u{200D}\u{1F3EB}` is 3 code points, but only 1 print position wide.
echo "This output should be 3 print positions wide, with leading and trailing `+`"
$"\u{1F9D1}\u{200D}\u{1F3EB}" | fill -c "+" -w 3 -a "c"
echo "This output should be 3 print positions wide, with leading and trailing `+`"
$"(ansi green)a(ansi reset)" | fill -c "+" -w 3 -a c
echo ""
```
Was producing this output:
```rust
This output should be 3 print positions wide, with leading and trailing `+`
🧑🏫
This output should be 3 print positions wide, with leading and trailing `+`
a
```
After this PR, it produces this output:
```rust
This output should be 3 print positions wide, with leading and trailing `+`
+🧑🏫+
This output should be 3 print positions wide, with leading and trailing `+`
+a+
```
# User-Facing Changes
Users may have to undo fixes they may have introduced to work around the
former behavior. I have one such in my prompt string that I can now
revert.
# Tests + Formatting
Don't forget to add tests that cover your changes.
-- Done
Make sure you've run and fixed any issues with these commands:
- [x] `cargo fmt --all -- --check` to check standard code formatting
(`cargo fmt --all` applies these changes)
- [x] `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- [x] `cargo test --workspace` to check that all tests pass
# After Submitting
`fill` command not documented in the book, and it still talks about `str
lpad/rpad`. I'll fix.
Note added dependency on a new library `print-positions`, which is an
iterator that yields a complete print position (cluster + Ansi sequence)
per call. Should this be vendored?
