deprecated_index: reject legacy splat expressions (#34)

Author: bendrucker

docs/rules/terraform_deprecated_index.md

@@ -25,9 +25,30 @@ Warning: List items should be accessed using square brackets (terraform_deprecat
 Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.1.0/docs/rules/terraform_deprecated_index.md
 ```
 
+```hcl
+locals {
+  list  = [{a = "b}, {a = "c"}]
+  value = list.*.a 
+}
+```
+
+```
+$ tflint
+1 issue(s) found:
+
+Warning: List items should be accessed using square brackets (terraform_deprecated_index)
+
+  on example.tf line 3:
+   3:   value = list.*.a
+
+Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.1.0/docs/rules/terraform_deprecated_index.md
+```
+
 ## Why
 
-Terraform v0.12 supports traditional square brackets for accessing list items by index. However, for backward compatability with v0.11, Terraform continues to support accessing list items with the dot syntax normally used for attributes. While Terraform does not print warnings for this syntax, it is no longer documented and its use is discouraged.
+Terraform v0.12 supports traditional square brackets for accessing list items by index or using the splat operator (`*`). However, for backward compatibility with v0.11, Terraform continues to support accessing list items with the dot syntax normally used for attributes. While Terraform does not print warnings for this syntax, it is no longer documented and its use is discouraged.
+
+* [Legacy Splat Expressions](https://developer.hashicorp.com/terraform/language/expressions/splat#legacy-attribute-only-splat-expressions)
 
 ## How To Fix
 

rules/terraform_deprecated_index.go

@@ -49,39 +49,49 @@ func (r *TerraformDeprecatedIndexRule) Check(runner tflint.Runner) error {
 	}
 
 	diags := runner.WalkExpressions(tflint.ExprWalkFunc(func(expr hcl.Expression) hcl.Diagnostics {
+		filename := expr.Range().Filename
+		file, err := runner.GetFile(filename)
+		if err != nil {
+			return hcl.Diagnostics{
+				{
+					Severity: hcl.DiagError,
+					Summary:  "failed to call GetFile()",
+					Detail:   err.Error(),
+				},
+			}
+		}
+
 		for _, variable := range expr.Variables() {
-			for _, traversal := range variable.SimpleSplit().Rel {
-				if traversal, ok := traversal.(hcl.TraverseIndex); ok {
-					filename := traversal.SrcRange.Filename
-					file, err := runner.GetFile(filename)
-					if err != nil {
-						return hcl.Diagnostics{
-							{
-								Severity: hcl.DiagError,
-								Summary:  "failed to call GetFile()",
-								Detail:   err.Error(),
-							},
-						}
-					}
-					bytes := traversal.SrcRange.SliceBytes(file.Bytes)
+			bytes := expr.Range().SliceBytes(file.Bytes)
 
-					tokens, diags := hclsyntax.LexExpression(bytes, filename, traversal.SrcRange.Start)
-					if diags.HasErrors() {
-						return diags
+			tokens, diags := hclsyntax.LexExpression(bytes, filename, variable.SourceRange().Start)
+			if diags.HasErrors() {
+				return diags
+			}
+
+			tokens = tokens[1:]
+
+			for i, token := range tokens {
+				if token.Type == hclsyntax.TokenDot {
+					if len(tokens) == i+1 {
+						return nil
 					}
 
-					if tokens[0].Type == hclsyntax.TokenDot {
-						if err := runner.EmitIssue(
-							r,
-							"List items should be accessed using square brackets",
-							expr.Range(),
-						); err != nil {
-							return hcl.Diagnostics{
-								{
-									Severity: hcl.DiagError,
-									Summary:  "failed to call EmitIssue()",
-									Detail:   err.Error(),
-								},
+					next := tokens[i+1].Type
+					if next == hclsyntax.TokenNumberLit || next == hclsyntax.TokenStar {
+						if tokens[0].Type == hclsyntax.TokenDot {
+							if err := runner.EmitIssue(
+								r,
+								"List items should be accessed using square brackets",
+								expr.Range(),
+							); err != nil {
+								return hcl.Diagnostics{
+									{
+										Severity: hcl.DiagError,
+										Summary:  "failed to call EmitIssue()",
+										Detail:   err.Error(),
+									},
+								}
 							}
 						}
 					}
@@ -91,6 +101,7 @@ func (r *TerraformDeprecatedIndexRule) Check(runner tflint.Runner) error {
 
 		return nil
 	}))
+
 	if diags.HasErrors() {
 		return diags
 	}

rules/terraform_deprecated_index_test.go

@@ -39,6 +39,32 @@ locals {
 				},
 			},
 		},
+		{
+			Name: "deprecated dot splat index style",
+			Content: `
+locals {
+  maplist = [{a = "b"}]
+  values = maplist.*.a
+}
+`,
+			Expected: helper.Issues{
+				{
+					Rule:    NewTerraformDeprecatedIndexRule(),
+					Message: "List items should be accessed using square brackets",
+					Range: hcl.Range{
+						Filename: "config.tf",
+						Start: hcl.Pos{
+							Line:   4,
+							Column: 12,
+						},
+						End: hcl.Pos{
+							Line:   4,
+							Column: 23,
+						},
+					},
+				},
+			},
+		},
 		{
 			Name: "attribute access",
 			Content: `