fix: improvements after code review

docs/rules/README.md

@@ -11,7 +11,7 @@ Below is a list of available rules.
 |[terraform_deprecated_interpolation](terraform_deprecated_interpolation.md)|Disallow deprecated (0.11-style) interpolation|✔|
 |[terraform_documented_outputs](terraform_documented_outputs.md)|Disallow `output` declarations without description||
 |[terraform_documented_variables](terraform_documented_variables.md)|Disallow `variable` declarations without description||
-|[terraform_empty_list_check](terraform_empty_list_check.md)|Disallow comparisons with `[]` when checking if a list is empty||
+|[terraform_empty_list_equality](terraform_empty_list_equality.md)|Disallow comparisons with `[]` when checking if a collection is empty||
 |[terraform_module_pinned_source](terraform_module_pinned_source.md)|Disallow specifying a git or mercurial repository as a module source without pinning to a version|✔|
 |[terraform_module_version](terraform_module_version.md)|Checks that Terraform modules sourced from a registry specify a version|✔|
 |[terraform_naming_convention](terraform_naming_convention.md)|Enforces naming conventions for resources, data sources, etc||

docs/rules/terraform_empty_list_check.md → docs/rules/terraform_empty_list_equality.md

@@ -1,6 +1,6 @@
-# terraform_empty_list_check
+# terraform_empty_list_equality
 
-Disallow comparisons with `[]` when checking if a list is empty.
+Disallow comparisons with `[]` when checking if a collection is empty.
 
 ## Example
 
@@ -18,19 +18,19 @@ resource "aws_db_instance" "mysql" {
 $ tflint
 1 issue(s) found:
 
-Warning: List is compared with [] instead of checking if length is 0. (terraform_empty_list_check)
+Warning: Comparing a collection with an empty list is invalid. To detect an empty collection, check its length. (terraform_empty_list_equality)
 
   on test.tf line 5:
    5:   count = var.my_list == [] ? 0 : 1
 
-Reference: https://github.com/terraform-linters/tflint/blob/master/docs/rules/terraform_empty_list_check.md
+Reference: https://github.com/terraform-linters/tflint/blob/master/docs/rules/terraform_empty_list_equality.md
  
 ```
 
 ## Why
 
-The `==` operator can only return true when the two operands have identical types, and the type of `[]` alone (without any further type conversions) is an empty tuple rather than a list of objects, strings, numbers or any other type. Therefore, a comparison with a single `[]` with the goal of checking if a list is empty, will always return false.
+The `==` operator can only return true when the two operands have identical types, and the type of `[]` alone (without any further type conversions) is an empty tuple rather than a list of objects, strings, numbers or any other type. Therefore, a comparison with a single `[]` with the goal of checking if a collection is empty, will always return false.
 
 ## How To Fix
 
-Check if a list is empty by checking its length instead. For example: `length(var.my_list) == 0`.
+Check if a collection is empty by checking its length instead. For example: `length(var.my_list) == 0`.

rules/provider.go

@@ -21,7 +21,7 @@ var DefaultRules = []Rule{
 	terraformrules.NewTerraformDeprecatedInterpolationRule(),
 	terraformrules.NewTerraformDocumentedOutputsRule(),
 	terraformrules.NewTerraformDocumentedVariablesRule(),
-	terraformrules.NewTerraformEmptyListCheckRule(),
+	terraformrules.NewTerraformEmptyListEqualityRule(),
 	terraformrules.NewTerraformModulePinnedSourceRule(),
 	terraformrules.NewTerraformModuleVersionRule(),
 	terraformrules.NewTerraformNamingConventionRule(),

rules/terraformrules/terraform_empty_list_check.go → rules/terraformrules/terraform_empty_list_equality.go

@@ -8,58 +8,51 @@ import (
 	"github.com/terraform-linters/tflint/tflint"
 )
 
-// TerraformEmptyListCheckRule checks whether is there a comparison with an empty list
-type TerraformEmptyListCheckRule struct{}
+// TerraformEmptyListEqualityRule checks whether is there a comparison with an empty list
+type TerraformEmptyListEqualityRule struct{}
 
 // NewTerraformCommentSyntaxRule returns a new rule
-func NewTerraformEmptyListCheckRule() *TerraformEmptyListCheckRule {
-	return &TerraformEmptyListCheckRule{}
+func NewTerraformEmptyListEqualityRule() *TerraformEmptyListEqualityRule {
+	return &TerraformEmptyListEqualityRule{}
 }
 
 // Name returns the rule name
-func (r *TerraformEmptyListCheckRule) Name() string {
-	return "terraform_empty_list_check"
+func (r *TerraformEmptyListEqualityRule) Name() string {
+	return "terraform_empty_list_equality"
 }
 
 // Enabled returns whether the rule is enabled by default
-func (r *TerraformEmptyListCheckRule) Enabled() bool {
+func (r *TerraformEmptyListEqualityRule) Enabled() bool {
 	return true
 }
 
 // Severity returns the rule severity
-func (r *TerraformEmptyListCheckRule) Severity() tflint.Severity {
+func (r *TerraformEmptyListEqualityRule) Severity() tflint.Severity {
 	return tflint.WARNING
 }
 
 // Link returns the rule reference link
-func (r *TerraformEmptyListCheckRule) Link() string {
+func (r *TerraformEmptyListEqualityRule) Link() string {
 	return tflint.ReferenceLink(r.Name())
 }
 
 // Check checks whether the list is being compared with static empty list
-func (r *TerraformEmptyListCheckRule) Check(runner *tflint.Runner) error {
+func (r *TerraformEmptyListEqualityRule) Check(runner *tflint.Runner) error {
 	if !runner.TFConfig.Path.IsRoot() {
 		// This rule does not evaluate child modules.
 		return nil
 	}
 
 	log.Printf("[TRACE] Check `%s` rule for `%s` runner", r.Name(), runner.TFConfigPath())
 
-	files := make(map[string]*struct{})
-	for _, variable := range runner.TFConfig.Module.Variables {
-		files[variable.DeclRange.Filename] = nil
-	}
-
-	for filename := range files {
-		if err := r.checkEmptyList(runner, filename); err != nil {
-			return err
-		}
+	if err := r.checkEmptyList(runner); err != nil {
+		return err
 	}
 
 	return nil
 }
 
-func (r *TerraformEmptyListCheckRule) checkEmptyList(runner *tflint.Runner, filename string) error {
+func (r *TerraformEmptyListEqualityRule) checkEmptyList(runner *tflint.Runner) error {
 	return runner.WalkExpressions(func(expr hcl.Expression) error {
 		if conditionalExpr, ok := expr.(*hclsyntax.ConditionalExpr); ok {
 			if binaryOpExpr, ok := conditionalExpr.Condition.(*hclsyntax.BinaryOpExpr); ok {
@@ -77,7 +70,7 @@ func (r *TerraformEmptyListCheckRule) checkEmptyList(runner *tflint.Runner, file
 	})
 }
 
-func checkEmptyList(tupleConsExpr *hclsyntax.TupleConsExpr, runner *tflint.Runner, r *TerraformEmptyListCheckRule, binaryOpExpr *hclsyntax.BinaryOpExpr) {
+func checkEmptyList(tupleConsExpr *hclsyntax.TupleConsExpr, runner *tflint.Runner, r *TerraformEmptyListEqualityRule, binaryOpExpr *hclsyntax.BinaryOpExpr) {
 	if len(tupleConsExpr.Exprs) == 0 {
 		runner.EmitIssue(
 			r,

rules/terraformrules/terraform_empty_list_check_test.go → rules/terraformrules/terraform_empty_list_equality_test.go

@@ -7,7 +7,7 @@ import (
 	"github.com/terraform-linters/tflint/tflint"
 )
 
-func Test_TerraformEmptyListCheckRule(t *testing.T) {
+func Test_TerraformEmptyListEqualityRule(t *testing.T) {
 	cases := []struct {
 		Name     string
 		Content  string
@@ -16,21 +16,27 @@ func Test_TerraformEmptyListCheckRule(t *testing.T) {
 		{
 			Name: "comparing with [] is not recommended",
 			Content: `
-variable "my_list" {
-	type = list(string)
-}
 resource "aws_db_instance" "mysql" {
-	count = var.my_list == [] ? 0 : 1
+	count = [] == [] ? 0 : 1
     instance_class = "m4.2xlarge"
 }`,
 			Expected: tflint.Issues{
 				{
-					Rule:    NewTerraformEmptyListCheckRule(),
-					Message: "List is compared with [] instead of checking if length is 0.",
+					Rule:    NewTerraformEmptyListEqualityRule(),
+					Message: "Comparing a collection with an empty list is invalid. To detect an empty collection, check its length.",
 					Range: hcl.Range{
 						Filename: "resource.tf",
-						Start:    hcl.Pos{Line: 6, Column: 10},
-						End:      hcl.Pos{Line: 6, Column: 27},
+						Start:    hcl.Pos{Line: 3, Column: 10},
+						End:      hcl.Pos{Line: 3, Column: 18},
+					},
+				},
+				{
+					Rule:    NewTerraformEmptyListEqualityRule(),
+					Message: "Comparing a collection with an empty list is invalid. To detect an empty collection, check its length.",
+					Range: hcl.Range{
+						Filename: "resource.tf",
+						Start:    hcl.Pos{Line: 3, Column: 10},
+						End:      hcl.Pos{Line: 3, Column: 18},
 					},
 				},
 			},
@@ -47,8 +53,8 @@ resource "aws_db_instance" "mysql" {
 }`,
 			Expected: tflint.Issues{
 				{
-					Rule:    NewTerraformEmptyListCheckRule(),
-					Message: "List is compared with [] instead of checking if length is 0.",
+					Rule:    NewTerraformEmptyListEqualityRule(),
+					Message: "Comparing a collection with an empty list is invalid. To detect an empty collection, check its length.",
 					Range: hcl.Range{
 						Filename: "resource.tf",
 						Start:    hcl.Pos{Line: 6, Column: 10},
@@ -71,7 +77,7 @@ resource "aws_db_instance" "mysql" {
 		},
 	}
 
-	rule := NewTerraformEmptyListCheckRule()
+	rule := NewTerraformEmptyListEqualityRule()
 
 	for _, tc := range cases {
 		runner := tflint.TestRunner(t, map[string]string{"resource.tf": tc.Content})