From 434a1637f85be46c1e6ee585d9d45be7531a5d8b Mon Sep 17 00:00:00 2001
From: Lucas Bajolet <lucas.bajolet@hashicorp.com>
Date: Fri, 25 Aug 2023 17:00:03 -0400
Subject: [PATCH] hcl2template: fix func to get vars from a config

The previous implementation of the GetVarsByType function worked only on
top-level attributes, ignoring the nested blocks in the structure.

This implies that if a datasource depends on another through an
expression within a nested block, we may not execute it first, and then
executing this datasource before its dependent is possible, resulting in
an error in the end.

This commit is an attempt at making this more reliable for HCL configs,
but only works on configs lifted from HCL files for now. We need to make
this more reliable for later iterations.
---
 hcl2template/utils.go | 52 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/hcl2template/utils.go b/hcl2template/utils.go
index a542a2467ac..ce9486ed676 100644
--- a/hcl2template/utils.go
+++ b/hcl2template/utils.go
@@ -11,6 +11,7 @@ import (
 
 	"github.com/gobwas/glob"
 	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/hcl/v2/hclsyntax"
 	"github.com/hashicorp/packer/hcl2template/repl"
 	hcl2shim "github.com/hashicorp/packer/hcl2template/shim"
 	"github.com/zclconf/go-cty/cty"
@@ -187,22 +188,47 @@ func ConvertPluginConfigValueToHCLValue(v interface{}) (cty.Value, error) {
 	return buildValue, nil
 }
 
+// GetVarsByType walks through a hcl body, and gathers all the Traversals that
+// have a root type matching one of the specified top-level labels.
+//
+// This will only work on finite, expanded, HCL bodies.
 func GetVarsByType(block *hcl.Block, topLevelLabels ...string) []hcl.Traversal {
-	attributes, _ := block.Body.JustAttributes()
-
-	var vars []hcl.Traversal
-
-	for _, attr := range attributes {
-		for _, variable := range attr.Expr.Variables() {
-			rootLabel := variable.RootName()
-			for _, label := range topLevelLabels {
-				if label == rootLabel {
-					vars = append(vars, variable)
-					break
-				}
+	var travs []hcl.Traversal
+
+	switch body := block.Body.(type) {
+	case *hclsyntax.Body:
+		travs = getVarsByTypeForHCLSyntaxBody(body)
+	default:
+		attrs, _ := body.JustAttributes()
+		for _, attr := range attrs {
+			travs = append(travs, attr.Expr.Variables()...)
+		}
+	}
+
+	var rets []hcl.Traversal
+	for _, t := range travs {
+		varRootname := t.RootName()
+		for _, lbl := range topLevelLabels {
+			if varRootname == lbl {
+				rets = append(rets, t)
+				break
 			}
 		}
 	}
 
-	return vars
+	return rets
+}
+
+func getVarsByTypeForHCLSyntaxBody(body *hclsyntax.Body) []hcl.Traversal {
+	var rets []hcl.Traversal
+
+	for _, attr := range body.Attributes {
+		rets = append(rets, attr.Expr.Variables()...)
+	}
+
+	for _, block := range body.Blocks {
+		rets = append(rets, getVarsByTypeForHCLSyntaxBody(block.Body)...)
+	}
+
+	return rets
 }