poc: Add JSON output to workspace list in a way that's non-breaking for human output

[SarahFrench]

Related to #37439

This PR

This PR shows how a command that still uses cli.Ui for human output could be changed to enable JSON output.

These changes include:

1. Making the command process arguments using the arguments package

terraform/internal/command/workspace_list.go

Lines 26 to 33 in 2cf22a7

	// c.Meta.process removes global flags (-no-color, -compact-warnings) and uses them to configure the Ui and View.
	//
	// Other command implementations remove those arguments via arguments.ParseView, instead. That is only possible if views
	// are used for both human and machine output. This command still uses cli.Ui for human output, so c.Meta.process is necessary.
	rawArgs = c.Meta.process(rawArgs)
	// Parse command-specific arguments.
	args, diags := arguments.ParseWorkspace(rawArgs)

2. Making the command use a views-like pattern to control how output is sent to streams, but preserving human-readable output being produced via cli.Ui to avoid breaking changes

terraform/internal/command/workspace_list.go

Lines 146 to 150 in 2cf22a7

	// newWorkspaceList returns a views.WorkspaceList interface.
	//
	// When human-readable output is migrated from cli.Ui to views.View this method should be deleted and
	// replaced with using views.NewWorkspaceList directly.
	func newWorkspaceList(vt arguments.ViewType, view *views.View, ui cli.Ui, meta *Meta) views.WorkspaceList {

3. The config path is now obtained like this, to avoid the ModulePath method that makes it hard to add new arguments/flags to arguments (see also #38358):

terraform/internal/command/workspace_list.go

Line 60 in 2cf22a7

configPath := c.WorkingDir.RootModuleDir()

4. I refactored the command's Run method to use a single List method on the view to render results and/or diagnostics:

Happy path:

terraform/internal/command/workspace_list.go

Line 91 in 2cf22a7

view.List(env, states, diags)

Unhappy path example:

terraform/internal/command/workspace_list.go

Lines 72 to 75 in 2cf22a7

	if wDiags.HasErrors() {
	view.List("", nil, diags)
	return 1
	}

Details

WorkspaceList interface

This PR adds an interface in the views package called WorkspaceList:

terraform/internal/command/views/workspace.go

Lines 18 to 20 in 2cf22a7

	type WorkspaceList interface {
	List(selected string, list []string, diags tfdiags.Diagnostics)
	}

When JSON output is produced it uses an implementation of that interface that's in the views package. That implementation uses a View internally.

When human-readable output is produced the WorkspaceList implementation is defined in the command package, because that implementation uses cli.Ui internally. This has to live in the command package as use of cli.Ui is coupled to the Meta.

JSON output is a static log

The new JSON output is a static log. Its top-level structure is the same regardless of outcome, making the JSON easier to consume.

In the happy path, including a warning, output looks like:

{
  "workspaces": [
    {
      "name": "default",
      "is_current": true
    },
    {
      "name": "dev",
      "is_current": false
    },
    {
      "name": "stage",
      "is_current": false
    },
    {
      "name": "prod",
      "is_current": false
    }
  ],
  "diagnostics": [
    {
      "severity": "warning",
      "summary": "Warning!",
      "detail": "Consider yourself warned."
    }
  ]
}

In the unhappy path output looks like:

{
  "workspaces": [],
  "diagnostics": [
    {
      "severity": "error",
      "summary": "Error from test",
      "detail": "This is a error from the mocked state store."
    }
  ]
}

Target Release

N/A

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

[SarahFrench]

Closing in favour of 2 PRs