Transition to Cobra CLI

[hculea]

The main differences from the KingPin Version of the CLI:

• The versioning system: while in the previous version commands like secrethub read --version would have been valid, in this version, the --version flag can only be called on the root command, i.e. secrethub --version.
• When the autocompletion script is installed (see the installation guide), there are flags which already have static autocompletion enabled. (for example, secrethub audit --output-format [tab][tab] will autocomplete to table or json ).
• The bug involving the NoEnvVar function from env.go not removing the environment variable corresponding to the flag it was called on has been solved.

• Adds -h shorthand for help texts.
• Shows help text if you don't provide a subcommand where one is required, e.g. secrethub repo

[jpcoenen]

I would say it's half-past-launch-time!

Because of the long list of commits that have gone back and forth, I think we should consider squashing these commits @florisvdg @SimonBarendse any opinions on this?

[SimonBarendse]

I'm usually not a big fan of squashing, as we may lose some context and motivation for a change. However, I can see how the current commit history of going back-and-forth may not be ideal to find the whole set of changes + motivation either. Therefore, I'd like to make an exception to my rule for this PR and suggest to squash the changes. The commit message of the squash should be very verbose and contain motivation for most of the changes.

[edif2008]

Here is a draft of the squash commit message.

Commit: Switch the CLI library from KingPin to Cobra

Description:

The change to cobra is made because KingPin is no longer maintained, and Cobra comes with more enhancements than KingPin.
The main one is enabling autocompletion for arguments besides command and flag completion.

The following list of key changes have been made in the codebase:

• add -h shorthand for help text
• refactor env.go file's functions into argument.go, app.go, and flag.go
• the versioning system: while in the previous version commands like secrethub read --version would have been valid, in this version, the --version flag can only be called on the root command, i.e. secrethub --version.
• the bug involving the NoEnvVar function from env.go not removing the environment variable corresponding to the flag it was called on has been solved.
• custom template similar to cobra's

For a more detailed version of the changes in the codebase, below is a sqashed version of the commits:

• 483605e - ba69bc7 -> Implement a first protorype of secrethub-cli with cobra (only secrethub read works)
• 7f24ee3 - 1b81c0c -> Change creation of all commands to a cobra-style one (based on first prototype)
• 5d1cddf - de0a964 -> Simplify command creation functionality, add completion functionality
• c16cb7c -> Remove dynamic path autocompletion (will be done in a seperate PR)
• 337b3d6 - 35c1b6a -> Make minor adjustments to the error message, improve code
• a6e678c - 7e519c6 -> Globalize argument registration
• 673bde5 -> Refactor command registerer
• f53515f - 39e7352 -> Improve flag creation functionality to make it similar to cobra's syntax
• b17eb7c -> Rename command receiver
• 3dc680d - 75f7fc2 -> Create an Argument struct for optimising argument creation and error handling
• d5c03e6 - 6d075df -> Implement a custom template for help text
• 2bf3b2b - 1753b22 -> Remove commeted code from KingPin
• 4070695 -> Adjust argument types
• 2bd4055 - 093e421 -> Update branch with new features from develop
• 6419165 - b6f159e -> Enable automcompletion installation from cli for bash, adjust arg struct, fix global flags
• a9b26c5 - 883cbad -> Attach env var value to the flag value
• 6b971e9 - deb7e11 -> Refactor cli structs (env, app, argument, flag)
• 5bf329b - b103c0e -> Fix completion error in installing SecretHub with .deb and .rpm packages, remove autocopletion installation
• 8591027 - 52d1c98 -> Improve code quality (better naming, removing comments, minor fixes)
• 81905e1 - bb65d49 -> Simplify debug and mlock flag creation
• 8ef95aa - 930ced9 -> Implement hidden command, document template functions, fix mkdir and persistent flags envar names, make CLI work with demo, simplify template
• 8c1a534 - 4051c7c -> Process environment variables for global flags in PersistentRunE, adjust argument struct fields, improve help and error texts, change PreRunE addition function signature
• f7560ef - 4c4ff88 -> Improve persistent flag functionality, fix mlock and debug flags, improve PreRunE addition function, simplify structures used as argument values, add error message for minimum arguments
• 3e66d13 - 34eac77 -> Fix default description for service init, improve argument error handling
• cfe813c - 961229a -> Make small final touches

[edif2008]

Here is the new draft of the squash commit

Commit: Switch the CLI library from KingPin to Cobra

Description:

The change to Cobra is made for two main reasons:

• KingPin is no longer maintained
• Cobra enables argument autocompletion in addition to command and flag completion

Also, Cobra comes with some other enhancements that make the CLI construction simpler and more consistent.

The following list of key changes have been made in the codebase:

1. Visible to the user:

   • custom template that is similar to cobra's; the following additions on top of the default cobra template were made:
     • group commands with subcommands under Management Commands section
     • add Arguments section for explaining the arguments
     • divide the help text from command's/flag's name in a separate column for readibility
   • add -h shorthand for help text
   • automatically show help text if the user does not provide a subcommand where one is required, e.g. secrethub repo
   • when the user does not provide the required number of arguments, the CLI will provide an error message similar to docker's
   • the versioning system: while in the previous version commands like secrethub read --version would have been valid, in this version, the --version flag can only be called on the root command, i.e. secrethub --version.

2. Visible to the developer

   • refactor env.go file's functions into argument.go, app.go, and flag.go for better maintainability
   • cobra's cutom template can be adjusted in cobra_template.go, located now in internals/cli
   • flag registration has a similar syntax to cobra's
   • argument registration is made using BindArguments and BindArgumentsArr (for commands that accept multiple arguments of the same type, e.g. secrethub mkdir), since KingPin includes argumnet registration, while cobra does not; this function enables the developer to save the argument's value to a variable that can be later used when executing the command
   • the bug involving the NoEnvVar function not removing the environment variable corresponding to the flag it was called on has been solved
   • CommandClause has two more new fields: Args (for linking variables to argument values), and flags (for enabling the link between the flag and its euqivalent environment variable)