Merge pull request #134 from hashicorp/expression_extensions

Support `count` and `count.index` references in blocks

This adds supports for count and count.index completion, hover, and semantic tokens inside blocks by introducing an `Extensions` field  to the `BodySchema` struct, and then adds `Count` as an extension point. Code is then added to detect if `Count` is set to true and the current block supports `count` usage. Whether or not the current block supports `count` is determined by the schema held in terraform-schema, which is added in hashicorp/terraform-schema#143.

Effort is made to only suggest `count` or `count.index` when appropriate. `Count` will be suggested if the current block schema supports it, and `count.index` will be suggested when `count` is defined in the current block.

Hover data for `count` and `count.index` is added here, and shows appropriate information depending on where it is requested. Hover information is *not* supported for string interpolation yet, that is to be added in a different set of work.

Semantic tokens are resolved for `count` and `count.index` inside blocks. Semantic tokens are *not* supported for string interpolation yet, that is to be added in a different set of work.

Author: jpogran

decoder/body_candidates.go

@@ -17,6 +17,17 @@ func (d *PathDecoder) bodySchemaCandidates(body *hclsyntax.Body, schema *schema.
 	candidates := lang.NewCandidates()
 	count := 0
 
+	if schema.Extensions != nil {
+		// check if count attribute "extension" is enabled here
+		if schema.Extensions.Count {
+			// check if count attribute is already declared, so we don't
+			// suggest a duplicate
+			if _, ok := body.Attributes["count"]; !ok {
+				candidates.List = append(candidates.List, countAttributeCandidate(editRng))
+			}
+		}
+	}
+
 	if len(schema.Attributes) > 0 {
 		attrNames := sortedAttributeNames(schema.Attributes)
 		for _, name := range attrNames {