Ion dump

[zslayton]

Description of changes:

• Running cargo build or cargo install will build the code in the ion-c submodule and link against the resulting libraries.
• Creates an ion dump command that wraps the ion-c CLI and exposes a limited number of options.
• Creates a structure that will make it straightforward to add new commands in the future.
• Adds an "API subject to change" warning to the README.md file.

Testing

If you don't already have it, you can install cargo using rustup.

git clone -b ion-dump https://github.com/amzn/ion-cli.git
cd ion-cli
git submodule update --init --recursive
cargo install --path . 

Example output for ion:

ion 0.1.0
The Ion Team <ion-team@amazon.com>

USAGE:
    ion <SUBCOMMAND>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

SUBCOMMANDS:
    dump    Prints Ion in the requested format
    help    Prints this message or the help of the given subcommand(s)

Example output for ion help dump:

ion-dump
Prints Ion in the requested format

USAGE:
    ion dump [OPTIONS] [input]...

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -f, --format <format>    Output format [default: pretty]  [values: binary, text, pretty]
    -o, --output <output>    Output file [default: STDOUT]

ARGS:
    <input>...    Input file [default: STDIN]

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[zslayton]

The project's directory structure and the contents of this file were inspired by cargo, which follows a similar pattern.

[pbcornell]

Are you/cargo making some distinction between "built-in" commands and some other type of commands? If not, perhaps the term is simply "subcommands" (here and elsewhere).

[zslayton]

Are you/cargo making some distinction between "built-in" commands and some other type of commands?

Yes. "Built-in" commands are part of the same ion executable (and so show up in the output of ion help) while "external" commands are (potentially 3rd party) executables installed separately on the user's $PATH. See #1 for some extra detail.

[pbcornell]

One question below, otherwise looks like a good starting place, and assuming we're comfortable changing the contract as discussions continue (I assume that's what you mean by "API subject to change" in the readme).

[pbcornell]

Are you/cargo making some distinction between "built-in" commands and some other type of commands? If not, perhaps the term is simply "subcommands" (here and elsewhere).