Ignore non-existent provider aliases (#519)

Author: wata727

rules/aws_resource_missing_tags.go

@@ -1,7 +1,6 @@
 package rules
 
 import (
-	"errors"
 	"fmt"
 	"sort"
 	"strings"
@@ -169,21 +168,11 @@ func (r *AwsResourceMissingTagsRule) Check(runner tflint.Runner) error {
 			// Override the provider alias if defined
 			if val, ok := resource.Body.Attributes[providerAttributeName]; ok {
 				provider, diagnostics := aws.DecodeProviderConfigRef(val.Expr, "provider")
-				providerAlias = provider.Alias
-
-				if _, hasProvider := providerTagsMap[providerAlias]; !hasProvider {
-					errString := fmt.Sprintf(
-						"The aws provider with alias \"%s\" doesn't exist.",
-						providerAlias,
-					)
-					logger.Error("Error querying provider tags: %s", errString)
-					return errors.New(errString)
-				}
-
 				if diagnostics.HasErrors() {
 					logger.Error("error decoding provider: %w", diagnostics)
 					return diagnostics
 				}
+				providerAlias = provider.Alias
 			}
 
 			// If the resource has a tags attribute

rules/aws_resource_missing_tags_test.go

@@ -1,7 +1,6 @@
 package rules
 
 import (
-	"errors"
 	"testing"
 
 	hcl "github.com/hashicorp/hcl/v2"
@@ -383,29 +382,6 @@ rule "aws_resource_missing_tags" {
 				},
 			},
 		},
-		{
-			Name: "Provider reference no existent",
-			Content: `provider "aws" {
-  alias = "zoom"
-  default_tags {
-    tags = {
-      "Foo": "Bar"
-    }
-  }
-}
-
-resource "aws_instance" "ec2_instance" {
-  provider = aws.west
-  instance_type = "t2.micro"
-}`,
-			Config: `
-rule "aws_resource_missing_tags" {
-  enabled = true
-  tags = ["Foo"]
-}`,
-			Expected: helper.Issues{},
-			RaiseErr: errors.New("The aws provider with alias \"west\" doesn't exist."),
-		},
 		{
 			Name: "Provider reference existent without tags definition",
 			Content: `provider "aws" {
@@ -514,6 +490,41 @@ rule "aws_resource_missing_tags" {
 }`,
 			Expected: helper.Issues{},
 		},
+		{
+			// In child modules, the provider declarations are passed implicitly or explicitly from the root module.
+			// In this case, it is not possible to refer to the provider's default_tags.
+			// Here, the strategy is to ignore default_tags rather than skip inspection of the tags.
+			Name: "provider aliases within child modules",
+			Content: `
+terraform {
+  required_providers {
+    aws = {
+      source = "hashicorp/aws"
+      configuration_aliases = [ aws.foo ]
+    }
+  }
+}
+
+resource "aws_instance" "ec2_instance" {
+  provider = aws.foo
+}`,
+			Config: `
+rule "aws_resource_missing_tags" {
+  enabled = true
+  tags = ["Foo", "Bar"]
+}`,
+			Expected: helper.Issues{
+				{
+					Rule:    NewAwsResourceMissingTagsRule(),
+					Message: "The resource is missing the following tags: \"Bar\", \"Foo\".",
+					Range: hcl.Range{
+						Filename: "module.tf",
+						Start:    hcl.Pos{Line: 11, Column: 1},
+						End:      hcl.Pos{Line: 11, Column: 39},
+					},
+				},
+			},
+		},
 	}
 
 	rule := NewAwsResourceMissingTagsRule()