Introduce Code Actions

[radeksimko]

Background

Code actions is one of the major features of LSP and there is a great number of use cases anticipated in the context of the Terraform LS: https://github.com/hashicorp/terraform-ls/issues?page=2&q=is%3Aopen+is%3Aissue+label%3AtextDocument%2FcodeAction

The hcl-lang library should therefore provide an abstraction layer to enable implementations of these actions so that servers can agree on how this is done.

While code actions can be useful on their own, a significant portion of them will relate to a diagnostic ("quick fixes"). Such actions can be built on top of PathDecoder.Validate() and PathDecoder.ValidateFile().

hcl-lang/decoder/validate.go

Line 18 in 8067e8d

func (d *PathDecoder) Validate(ctx context.Context) (lang.DiagnosticsMap, error) {

hcl-lang/decoder/validate.go

Line 45 in 8067e8d

func (d *PathDecoder) ValidateFile(ctx context.Context, filename string) (hcl.Diagnostics, error) {

Proposal

• Introduce Code to Diagnostic hcl#647
• Ensure existing validators in the validator package produce diagnostics with appropriate unique Code
• New DecoderContext field:

CodeActions []lang.CodeActionImpl

• New decoder.Decoder method:

func (d *Decoder) CodeActionsForRange(ctx context.Context, path lang.Path, rng hcl.Range) []lang.CodeAction

• New decodercontext package:

func CodeAction(ctx context.Context) CodeActionContext {
	return ctx.Value(codeActionCtxKey{}).(CodeActionContext)
}

type CodeActionContext struct {
	Diagnostics []lang.Diagnostic
	Only        []lang.CodeActionKind
	TriggerKind lang.CodeActionTriggerKind
}

• New types in lang:

type CodeActionImpl interface {
   CodeActionKind() CodeActionKind
   CodeActions(ctx context.Context, path Path, rng hcl.Range) []CodeAction
   // TODO: ResolveCodeAction(CodeAction) CodeAction
}

type CodeAction struct {
   Title string
   Kind  CodeActionKind

   Diagnostics hcl.Diagnostics
   Edit        Edit
   Command     Command
}

type editSigil struct{}

type Edit interface {
   isEditImpl() editSigil
}

type FileEdits []TextEdit

func (fe FileEdits) isEditImpl() editSigil {
   return editSigil{}
}

type CodeActionKind string
type CodeActionTriggerKind string

Implementation Prototype

https://github.com/hashicorp/hcl-lang/compare/f-code-actions-prototype

Notes

The initial scope of this work is to enable single-file scoped code actions. The proposed abstraction should allow later expansion for multi-file and multi-folder support though.