aws_resource_missing_tags: use empty string for default provider

Uses empty string instead of "default" as the map key for the default
provider. This is cleaner and more consistent with what
DecodeProviderConfigRef returns when no alias is specified.

Fixes #1002

Author: bendrucker

rules/aws_resource_missing_tags.go

@@ -83,10 +83,10 @@ func (r *AwsResourceMissingTagsRule) getProviderLevelTags(runner tflint.Runner)
 	allProviderTags := make(map[string][]string)
 	var providerAlias string
 	for _, provider := range providerBody.Blocks.OfType(providerAttributeName) {
-		// Get the alias attribute, in terraform when there is a single aws provider its called "default"
+		// Get the alias attribute. Empty string represents the default provider.
 		providerAttr, ok := provider.Body.Attributes["alias"]
 		if !ok {
-			providerAlias = "default"
+			providerAlias = ""
 		} else {
 			err := runner.EvaluateExpr(providerAttr.Expr, func(alias string) error {
 				logger.Debug("Walk `%s` provider", providerAlias)
@@ -164,7 +164,7 @@ func (r *AwsResourceMissingTagsRule) Check(runner tflint.Runner) error {
 		}
 
 		for _, resource := range resources.Blocks {
-			providerAlias := "default"
+			var providerAlias string
 			// Override the provider alias if defined
 			if val, ok := resource.Body.Attributes[providerAttributeName]; ok {
 				provider, diagnostics := aws.DecodeProviderConfigRef(val.Expr, "provider")

rules/aws_resource_missing_tags_test.go

@@ -525,6 +525,30 @@ rule "aws_resource_missing_tags" {
 				},
 			},
 		},
+		{
+			Name: "Provider reference without alias (issue #1002)",
+			Content: `
+provider "aws" {
+  region = "eu-west-1"
+  default_tags {
+    tags = {
+      "layer": "app"
+      "type": "service"
+    }
+  }
+}
+
+resource "aws_iam_user" "bedrock" {
+  provider = aws
+  name = "test"
+}`,
+			Config: `
+rule "aws_resource_missing_tags" {
+  enabled = true
+  tags = ["layer", "type"]
+}`,
+			Expected: helper.Issues{},
+		},
 	}
 
 	rule := NewAwsResourceMissingTagsRule()