terraform/lang: Implement resource completion

Closes #9

Author: radeksimko

internal/terraform/lang/config_block.go

@@ -1,8 +1,12 @@
 package lang
 
 import (
+	"fmt"
+	"log"
+
 	hcl "github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/hcl/v2/hclsyntax"
+	tfjson "github.com/hashicorp/terraform-json"
 	lsp "github.com/sourcegraph/go-lsp"
 )
 
@@ -15,3 +19,109 @@ type ConfigBlock interface {
 type configBlockFactory interface {
 	New(*hclsyntax.Block) (ConfigBlock, error)
 }
+
+type completableBlock struct {
+	logger   *log.Logger
+	caps     lsp.TextDocumentClientCapabilities
+	hclBlock *hclsyntax.Block
+	schema   *tfjson.SchemaBlock
+}
+
+func (cb *completableBlock) completionItemsAtPos(pos hcl.Pos) (lsp.CompletionList, error) {
+	list := lsp.CompletionList{}
+
+	cb.logger.Printf("block: %#v", cb.hclBlock)
+
+	block := ParseBlock(cb.hclBlock, cb.schema)
+
+	if !block.PosInBody(pos) {
+		// Avoid autocompleting outside of body, for now
+		cb.logger.Println("avoiding completion outside of block body")
+		return list, nil
+	}
+
+	if block.PosInAttribute(pos) {
+		cb.logger.Println("avoiding completion in the middle of existing attribute")
+		return list, nil
+	}
+
+	b, ok := block.BlockAtPos(pos)
+	if !ok {
+		// This should never happen as the completion
+		// should only be called on a block the "pos" points to
+		cb.logger.Printf("block type not found at %#v", pos)
+		return list, nil
+	}
+
+	for name, attr := range b.Attributes() {
+		if attr.IsComputedOnly() || attr.IsDeclared() {
+			continue
+		}
+		list.Items = append(list.Items, cb.completionItemForAttr(name, attr, pos))
+	}
+
+	for name, block := range b.BlockTypes() {
+		if block.ReachedMaxItems() {
+			continue
+		}
+		list.Items = append(list.Items, cb.completionItemForNestedBlock(name, block, pos))
+	}
+
+	sortCompletionItems(list.Items)
+
+	return list, nil
+}
+
+func (cb *completableBlock) completionItemForAttr(name string, attr *Attribute, pos hcl.Pos) lsp.CompletionItem {
+	snippetSupport := cb.caps.Completion.CompletionItem.SnippetSupport
+
+	if snippetSupport {
+		return lsp.CompletionItem{
+			Label:            name,
+			Kind:             lsp.CIKField,
+			InsertTextFormat: lsp.ITFSnippet,
+			Detail:           schemaAttributeDetail(attr.Schema()),
+			TextEdit: &lsp.TextEdit{
+				Range: lsp.Range{
+					Start: lsp.Position{Line: pos.Line - 1, Character: pos.Column - 1},
+					End:   lsp.Position{Line: pos.Line - 1, Character: pos.Column - 1},
+				},
+				NewText: fmt.Sprintf("%s = %s", name, snippetForAttrType(0, attr.Schema().AttributeType)),
+			},
+		}
+	}
+
+	return lsp.CompletionItem{
+		Label:            name,
+		Kind:             lsp.CIKField,
+		InsertTextFormat: lsp.ITFPlainText,
+		Detail:           schemaAttributeDetail(attr.Schema()),
+	}
+}
+
+func (cb *completableBlock) completionItemForNestedBlock(name string, blockType *BlockType, pos hcl.Pos) lsp.CompletionItem {
+	snippetSupport := cb.caps.Completion.CompletionItem.SnippetSupport
+
+	if snippetSupport {
+		return lsp.CompletionItem{
+			Label:            name,
+			Kind:             lsp.CIKField,
+			InsertTextFormat: lsp.ITFSnippet,
+			Detail:           schemaBlockDetail(blockType),
+			TextEdit: &lsp.TextEdit{
+				Range: lsp.Range{
+					Start: lsp.Position{Line: pos.Line - 1, Character: pos.Column - 1},
+					End:   lsp.Position{Line: pos.Line - 1, Character: pos.Column - 1},
+				},
+				NewText: snippetForNestedBlock(name),
+			},
+		}
+	}
+
+	return lsp.CompletionItem{
+		Label:            name,
+		Kind:             lsp.CIKField,
+		InsertTextFormat: lsp.ITFPlainText,
+		Detail:           schemaBlockDetail(blockType),
+	}
+}