decoder: Add support for Reference as Constraint (#185)

* schema: Implement EmptyCompletionData for Reference

* decoder: Implement completion for Reference

* decoder: Implement hover for Reference

* decoder: Implement semantic tokens for Reference

* decoder: Implement reference origins for Reference

* decoder: Implement reference targets for Reference

decoder/expr_reference.go

@@ -1,40 +1,12 @@
 package decoder
 
 import (
-	"context"
-
-	"github.com/hashicorp/hcl-lang/lang"
-	"github.com/hashicorp/hcl-lang/reference"
 	"github.com/hashicorp/hcl-lang/schema"
 	"github.com/hashicorp/hcl/v2"
 )
 
 type Reference struct {
-	expr hcl.Expression
-	cons schema.Reference
-}
-
-func (ref Reference) CompletionAtPos(ctx context.Context, pos hcl.Pos) []lang.Candidate {
-	// TODO
-	return nil
-}
-
-func (ref Reference) HoverAtPos(ctx context.Context, pos hcl.Pos) *lang.HoverData {
-	// TODO
-	return nil
-}
-
-func (ref Reference) SemanticTokens(ctx context.Context) []lang.SemanticToken {
-	// TODO
-	return nil
-}
-
-func (ref Reference) ReferenceOrigins(ctx context.Context, allowSelfRefs bool) reference.Origins {
-	// TODO
-	return nil
-}
-
-func (ref Reference) ReferenceTargets(ctx context.Context, targetCtx *TargetContext) reference.Targets {
-	// TODO
-	return nil
+	expr    hcl.Expression
+	cons    schema.Reference
+	pathCtx *PathContext
 }

decoder/expr_reference_completion.go

@@ -0,0 +1,99 @@
+package decoder
+
+import (
+	"context"
+
+	"github.com/hashicorp/hcl-lang/lang"
+	"github.com/hashicorp/hcl-lang/reference"
+	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/hcl/v2/hclsyntax"
+)
+
+func (ref Reference) CompletionAtPos(ctx context.Context, pos hcl.Pos) []lang.Candidate {
+	if ref.cons.Address != nil {
+		// no candidates if traversal itself is addressable
+		return []lang.Candidate{}
+	}
+
+	if ref.pathCtx.ReferenceTargets == nil {
+		return []lang.Candidate{}
+	}
+
+	file := ref.pathCtx.Files[ref.expr.Range().Filename]
+	rootBody, ok := file.Body.(*hclsyntax.Body)
+	if !ok {
+		return []lang.Candidate{}
+	}
+
+	outerBodyRng := rootBody.Range()
+	// Find outer block body range to allow filtering
+	// of references pointing back to the same block
+	outerBlock := rootBody.OutermostBlockAtPos(pos)
+	if outerBlock != nil {
+		ob := outerBlock.Body.(*hclsyntax.Body)
+		outerBodyRng = ob.Range()
+	}
+
+	if isEmptyExpression(ref.expr) {
+		editRng := hcl.Range{
+			Filename: ref.expr.Range().Filename,
+			Start:    pos,
+			End:      pos,
+		}
+		candidates := make([]lang.Candidate, 0)
+		ref.pathCtx.ReferenceTargets.MatchWalk(ctx, ref.cons, "", outerBodyRng, editRng, func(target reference.Target) error {
+			address := target.Address(ctx, editRng.Start).String()
+
+			candidates = append(candidates, lang.Candidate{
+				Label:       address,
+				Detail:      target.FriendlyName(),
+				Description: target.Description,
+				Kind:        lang.TraversalCandidateKind,
+				TextEdit: lang.TextEdit{
+					NewText: address,
+					Snippet: address,
+					Range:   editRng,
+				},
+			})
+			return nil
+		})
+		return candidates
+	}
+
+	eType, ok := ref.expr.(*hclsyntax.ScopeTraversalExpr)
+	if !ok {
+		return []lang.Candidate{}
+	}
+
+	editRng := eType.Range()
+	if !editRng.ContainsPos(pos) {
+		// account for trailing character(s) which doesn't appear in AST
+		// such as dot, opening bracket etc.
+		editRng.End = pos
+	}
+	prefixRng := hcl.Range{
+		Filename: eType.Range().Filename,
+		Start:    eType.Range().Start,
+		End:      pos,
+	}
+	prefix := string(prefixRng.SliceBytes(file.Bytes))
+
+	candidates := make([]lang.Candidate, 0)
+	ref.pathCtx.ReferenceTargets.MatchWalk(ctx, ref.cons, prefix, outerBodyRng, editRng, func(target reference.Target) error {
+		address := target.Address(ctx, editRng.Start).String()
+
+		candidates = append(candidates, lang.Candidate{
+			Label:       address,
+			Detail:      target.FriendlyName(),
+			Description: target.Description,
+			Kind:        lang.TraversalCandidateKind,
+			TextEdit: lang.TextEdit{
+				NewText: address,
+				Snippet: address,
+				Range:   editRng,
+			},
+		})
+		return nil
+	})
+	return candidates
+}