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This small Go app is for testing Cobra's shell completion capabilities.

Build:

$ go build -o emu-cli ./cmd/emu-cli # build CLI built with urfave/cli
$ go build -o emu-cobra ./cmd/emu-cobra # build CLI built with spf13/cobra

Source completions for the current shell:

$ . <(./emu-cli completion zsh)
$ . <(./emu-cobra completion zsh)

Test command completion:

$ ./emu-cli r[tab]
completion  -- Generate the autocompletion script for the specified shell
help        -- Help about any command
run         -- Run app on device

Test flag completion:

$ ./emu-cli --device [tab]
Barteks-iPhone  emulator-5554

Shell completion in spf13/cobra – feature overview

To test out various shell completion features, we'll build out a hypothetical simple app for controlling Android emulators and iOS simulators.

Examples

Complete commands

t=1

$ ./emu-cli [tab]
create  -- Create a new device
kill    -- Kill a single device
run     -- Start a single device
runall  -- Start many devices

t=1

$ ./emu-cli r[tab]
run     -- Start a single device
runall  -- Start many devices

Complete a single command argument

Use case: when an option has been selected, don't suggest any more completions.

t=1

$ ./emu-cli run [tab]
Pixel 7 API 34
iPhone 12 mini
iPhone 15

t=2

$ ./emu-cli run Pixel\ 7\ API\ 34 [tab] # nothing appears, selection has been made

The default Zsh behavior is dependent upon some zstyle options. By default, it suggests files in $pwd.

Complete single element (with flags)

Similar to the previous one, but should suggest subcommand's flags instead when user's entry starts with - or --.

t=1

$ ./emu-cli run --[tab]
--fast
--slow

t=2

$ ./emu-cli run --fast [tab]
Pixel 7 API 34
iPhone 12 mini
iPhone 15

Complete finite set of elements

Use case: when a single option is selected, keep suggesting options but exclude the options already completed/entered/selected.

t=1

$ ./emu-cli run [tab]
Pixel 7 API 34
iPhone 12 mini
iPhone 15

t=1

$ ./emu-cli run Pixel 7 API 34 [tab]
iPhone 12 mini
iPhone 15

t=2

./emu-cli run Pixel 7 API 34 iPhone 12 mini

Complete a single value for a flag element (with flags)

Similar to the previous one, but in this case (when current arguments starts with - or --) we want to suggests the values available for a particular flag.

$ TODO: invent some example (e.g. --device [value])

Debugging

Cobra docs

./emu-cli __complete run ""
Pixel 7 API 34
iPhone 12 mini
iPhone 15
:4
Completion ended with directive: ShellCompDirectiveNoFileComp

![NOTE] The :4

is the directive.

cobra.CompDebugln("this string will appear in __complete output", true)
cobra.CompDebugln("this will not appear there", false)

To see all traces from Cobra's completion system, set BASH_COMP_DEBUG_FILE env var:

$ export BASH_COMP_DEBUG_FILE="$PWD/cobra.log"

Testing

Shell completion in urfave/cli

To enable debug logging:

$ export URFAVE_CLI_TRACING=on

The plan

API changes:

  • Add cli.ShellCompleteFunc func type, same as in cobra

** Decision to be made**

Does urfave/cli migrate to hidden __complete command, or does it keep --generate-shell-completion arg?

  • This is quite hard, writing tests first is probably good idea. Take a look at how shell completion is tested in Cobra.