Add support for shell completion

[chevdor]

The Polkadot cli command now supports shell auto-completion.
The auto-completion is now generated from the build. Once executed, this script show the following if you type polkadot <tab><tab>:

$ polkadot 
--base-path      --collator       --help           --light          --no-telemetry   --pruning        --telemetry-url  --ws-port        -h               build-spec       import-blocks    
--bootnodes      --dev            --key            --log            --node-key       --rpc-port       --validator      -V               -l               export-blocks    
--chain          --execution      --keystore-path  --name           --port           --telemetry      --version        -d               -t               help     

The completion script is generated from cli.yml so it will keep in sync as the command and flags evolve.

See it in action below:

Assuming you built a release version using cargo build --release and use bash run the followig:

source target/release/completion-scripts/polkadot.bash

You can find completion scripts for:

• bash
• fish
• zsh
• elvish
• powershell

[tomusdrw]

Maybe better to add a CLI option to generate that in runtime?

polkadot cli-completion > polkadot.bash

Makes different version management easier, since you just obtain the binary and generate the completions for yourself locally.

[chevdor]

Hi @tomusdrw, thanks for your feedback.

I was considering it but went for a build only option in order to not overload the cli with code that is used only once at most and keep the polkadot cli as slim as possible but this is something that can be changed of course.

It may be even worth having this as feature.

If we decide to augment the cli, we will also need to pass and validate the shell:

polkadot cli-completion bash > polkadot.bash
polkadot cli-completion powershell > polkadot.ps1
...

[rphmeier]

typo: followig

[chevdor]

Thanks, fixed.

[rphmeier]

remaining commented println