Args can now be added to custom help sections. This breaks up the builder pattern a little by adding help section declarations inline, but it's the most intuitive method and doesn't require strange nesting that feels awkward.
```rust
app::new("foo")
.arg(Arg::with_name("arg1")) // under normal headers
.help_heading("SPECIAL")
.arg(Arg::with_name("arg2")) // under SPECIAL: heading
```
Closes#805
Add logic to filter based on hidden long/short.
There is still an issue with the logic in parser.rs use_long_help. This
causes invalid evaluation of whether to show/hide based on long or short help
Complete check for use_long_help, add tests
For version 3, we want the args section to immediately follow
the usage section in the default help message.
One change that I am unhappy with is needing to make "write_arg"
in app/help.rs accept an extra param that makes it suppress the
extra line. This is to prevent an extra blank line from appearing
between args and options in the default help, and seems necessary,
but there might be a better way.
Optional positionals mixed with subcommands will still break this, since
I can't see how to tell which element of $line is the command than.
Mixing optional positionals with subcommands is a bit weird and awkward
though...
This changes the way we complete positionals to complete them using
_arguments, as should be done, instead of completing their uppercase name
as a string.
Currently I made it offer _files completion for all positional arguments.
This can be improved to complete actual possible values of the arguments
and only complete files if the argument truly takes them. But this will
require further changes in clap to actually have the required
functionality to get this information.
Long options take their argument either in the next word or after an
equals sign, but the Zsh completion specified that they take it either
in the same word with no separator or in the next word. See the
documentation of the Zsh _arguments function for more information.
