Add option to disallow multi-line comments in terraform_comment_syntax rule

docs/rules/terraform_comment_syntax.md

@@ -2,6 +2,21 @@
 
 Disallow `//` comments in favor of `#`.
 
+## Configuration
+
+Name | Default | Value
+--- | --- | ---
+enabled | true | Boolean
+allow_multiline | false | Boolean
+
+```hcl
+rule "terraform_comment_syntax" {
+  enabled = true
+
+  allow_multiline = false
+}
+```
+
 ## Example
 
 ```hcl
@@ -18,7 +33,25 @@ Warning: Single line comments should begin with # (terraform_comment_syntax)
   on main.tf line 2:
    2: // Bad
 
-Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.1.0/docs/rules/terraform_comment_syntax.md
+Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.14.0/docs/rules/terraform_comment_syntax.md
+```
+
+### allow_multiline = false
+
+Disallows usage of multi-line comments.
+
+```hcl
+# Good
+/* Bad */
+```
+
+```
+Warning: Multi-line comments are not allowed. Use single-line comments starting with # (terraform_comment_syntax)
+
+  on main.tf line 1:
+   2: /* Bad */
+
+Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.14.0/docs/rules/terraform_comment_syntax.md
 ```
 
 ## Why
@@ -27,6 +60,12 @@ The Terraform language supports two different syntaxes for single-line comments:
 
 * [Configuration Syntax: Comments](https://developer.hashicorp.com/terraform/language/syntax/configuration#comments)
 
+Terraform also supports multi-line comments using `/*` and `*/` as delimiters. However, there's rarely a use-case where
+it makes sense to use multi-line comments over multiple single-line comments. Additionally, modern editors make it easy
+to work with single-line comments, and therefore it makes sense to disallow multi-line comments so there's only one syntax 
+for comments.
+
 ## How To Fix
 
 Replace the leading double-slash (`//`) in your comment with the number sign (`#`).
+Replace multi-line comments with multiple single-line comments if `allow_multiline = false` (default).

rules/terraform_comment_syntax.go

@@ -14,6 +14,10 @@ type TerraformCommentSyntaxRule struct {
 	tflint.DefaultRule
 }
 
+type terraformCommentSyntaxRuleConfig struct {
+	AllowMultiline bool `hclext:"allow_multiline,optional"`
+}
+
 // NewTerraformCommentSyntaxRule returns a new rule
 func NewTerraformCommentSyntaxRule() *TerraformCommentSyntaxRule {
 	return &TerraformCommentSyntaxRule{}
@@ -50,20 +54,25 @@ func (r *TerraformCommentSyntaxRule) Check(runner tflint.Runner) error {
 		return nil
 	}
 
+	config := terraformCommentSyntaxRuleConfig{AllowMultiline: false}
+	if err := runner.DecodeRuleConfig(r.Name(), &config); err != nil {
+		return err
+	}
+
 	files, err := runner.GetFiles()
 	if err != nil {
 		return err
 	}
 	for name, file := range files {
-		if err := r.checkComments(runner, name, file); err != nil {
+		if err := r.checkComments(runner, name, file, config.AllowMultiline); err != nil {
 			return err
 		}
 	}
 
 	return nil
 }
 
-func (r *TerraformCommentSyntaxRule) checkComments(runner tflint.Runner, filename string, file *hcl.File) error {
+func (r *TerraformCommentSyntaxRule) checkComments(runner tflint.Runner, filename string, file *hcl.File, allowMultiline bool) error {
 	if strings.HasSuffix(filename, ".json") {
 		return nil
 	}
@@ -74,11 +83,11 @@ func (r *TerraformCommentSyntaxRule) checkComments(runner tflint.Runner, filenam
 	}
 
 	for _, token := range tokens {
-		if token.Type != hclsyntax.TokenComment {
+		if token.Type != hclsyntax.TokenComment || token.Bytes[0] == '#' {
 			continue
 		}
 
-		if strings.HasPrefix(string(token.Bytes), "//") {
+		if token.Bytes[1] == '/' {
 			if err := runner.EmitIssueWithFix(
 				r,
 				"Single line comments should begin with #",
@@ -89,6 +98,14 @@ func (r *TerraformCommentSyntaxRule) checkComments(runner tflint.Runner, filenam
 			); err != nil {
 				return err
 			}
+		} else if !allowMultiline && token.Bytes[1] == '*' {
+			if err := runner.EmitIssue(
+				r,
+				"Multi-line comments are not allowed. Use single-line comments starting with #",
+				token.Range,
+			); err != nil {
+				return err
+			}
 		}
 	}
 

rules/terraform_comment_syntax_test.go

@@ -11,6 +11,7 @@ func Test_TerraformCommentSyntaxRule(t *testing.T) {
 	cases := []struct {
 		Name     string
 		Content  string
+		Config   string
 		JSON     bool
 		Expected helper.Issues
 		Fixed    string
@@ -21,14 +22,46 @@ func Test_TerraformCommentSyntaxRule(t *testing.T) {
 			Expected: helper.Issues{},
 		},
 		{
-			Name: "multi-line comment",
+			Name: "multi-line comment allowed",
 			Content: `
 /*
 	This comment spans multiple lines
 */			
+`,
+			Config: `
+rule "terraform_comment_syntax" {
+  enabled = true
+
+  allow_multiline = true
+}
 `,
 			Expected: helper.Issues{},
 		},
+		{
+			Name: "multi-line comment disallowed",
+			Content: `
+/*
+	This comment spans multiple lines
+*/			
+`,
+			Expected: helper.Issues{
+				{
+					Rule:    NewTerraformCommentSyntaxRule(),
+					Message: "Multi-line comments are not allowed. Use single-line comments starting with #",
+					Range: hcl.Range{
+						Filename: "variables.tf",
+						Start: hcl.Pos{
+							Line:   2,
+							Column: 1,
+						},
+						End: hcl.Pos{
+							Line:   4,
+							Column: 3,
+						},
+					},
+				},
+			},
+		},
 		{
 			Name:    "double-slash comment",
 			Content: `// foo`,
@@ -77,7 +110,7 @@ variable "foo" {
 				filename += ".json"
 			}
 
-			runner := helper.TestRunner(t, map[string]string{filename: tc.Content})
+			runner := helper.TestRunner(t, map[string]string{filename: tc.Content, ".tflint.hcl": tc.Config})
 
 			if err := rule.Check(runner); err != nil {
 				t.Fatalf("Unexpected error occurred: %s", err)