From 025252c0de5bd0061b033c35c785efd07693c97c Mon Sep 17 00:00:00 2001
From: Kei Sakamoto <thiry27015@gmail.com>
Date: Tue, 2 Dec 2025 19:02:59 +0900
Subject: [PATCH] feat: implement no-sparse-arrays

---
 internal/config/config.go                     |  2 +
 .../no_sparse_arrays/no_sparse_arrays.go      | 25 ++++++++
 .../no_sparse_arrays/no_sparse_arrays_test.go | 58 +++++++++++++++++++
 3 files changed, 85 insertions(+)
 create mode 100644 internal/rules/no_sparse_arrays/no_sparse_arrays.go
 create mode 100644 internal/rules/no_sparse_arrays/no_sparse_arrays_test.go

diff --git a/internal/config/config.go b/internal/config/config.go
index c43fab90..a796d856 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -95,6 +95,7 @@ import (
 	"github.com/web-infra-dev/rslint/internal/rules/no_constant_condition"
 	"github.com/web-infra-dev/rslint/internal/rules/no_constructor_return"
 	"github.com/web-infra-dev/rslint/internal/rules/no_debugger"
+	"github.com/web-infra-dev/rslint/internal/rules/no_sparse_arrays"
 )
 
 // RslintConfig represents the top-level configuration array
@@ -459,6 +460,7 @@ func registerAllCoreEslintRules() {
 	GlobalRuleRegistry.Register("no-constant-condition", no_constant_condition.NoConstantConditionRule)
 	GlobalRuleRegistry.Register("no-constructor-return", no_constructor_return.NoConstructorReturnRule)
 	GlobalRuleRegistry.Register("no-debugger", no_debugger.NoDebuggerRule)
+	GlobalRuleRegistry.Register("no-sparse-arrays", no_sparse_arrays.NoSparseArraysRule)
 }
 
 // getAllTypeScriptEslintPluginRules returns all registered rules (for backward compatibility when no config is provided)
diff --git a/internal/rules/no_sparse_arrays/no_sparse_arrays.go b/internal/rules/no_sparse_arrays/no_sparse_arrays.go
new file mode 100644
index 00000000..3184fcac
--- /dev/null
+++ b/internal/rules/no_sparse_arrays/no_sparse_arrays.go
@@ -0,0 +1,25 @@
+package no_sparse_arrays
+
+import (
+	"github.com/microsoft/typescript-go/shim/ast"
+	"github.com/web-infra-dev/rslint/internal/rule"
+)
+
+// https://eslint.org/docs/latest/rules/no-sparse-arrays
+var NoSparseArraysRule = rule.Rule{
+	Name: "no-sparse-arrays",
+	Run: func(ctx rule.RuleContext, options any) rule.RuleListeners {
+		return rule.RuleListeners{
+			ast.KindArrayLiteralExpression: func(node *ast.Node) {
+				for _, v := range node.AsArrayLiteralExpression().Elements.Nodes {
+					if v.Kind == ast.KindOmittedExpression {
+						ctx.ReportNode(node, rule.RuleMessage{
+							Id:          "unexpectedSparseArray",
+							Description: "Unexpected comma in middle of array.",
+						})
+					}
+				}
+			},
+		}
+	},
+}
diff --git a/internal/rules/no_sparse_arrays/no_sparse_arrays_test.go b/internal/rules/no_sparse_arrays/no_sparse_arrays_test.go
new file mode 100644
index 00000000..ad88a483
--- /dev/null
+++ b/internal/rules/no_sparse_arrays/no_sparse_arrays_test.go
@@ -0,0 +1,58 @@
+package no_sparse_arrays
+
+import (
+	"testing"
+
+	"github.com/web-infra-dev/rslint/internal/plugins/typescript/rules/fixtures"
+	"github.com/web-infra-dev/rslint/internal/rule_tester"
+)
+
+func TestNoSparseArraysRule(t *testing.T) {
+	rule_tester.RunRuleTester(
+		fixtures.GetRootDir(),
+		"tsconfig.json",
+		t,
+		&NoSparseArraysRule,
+		// Valid cases - ported from ESLint
+		[]rule_tester.ValidTestCase{
+			{Code: `var a = [ 1, 2, ]`},
+		},
+		// Invalid cases - ported from ESLint
+		[]rule_tester.InvalidTestCase{
+			{
+				Code: `var a = [,];`,
+				Errors: []rule_tester.InvalidTestCaseError{
+					{MessageId: "unexpectedSparseArray", Line: 1, Column: 9},
+				},
+			},
+			{
+				Code: `var a = [ 1,, 2];`,
+				Errors: []rule_tester.InvalidTestCaseError{
+					{MessageId: "unexpectedSparseArray", Line: 1, Column: 9},
+				},
+			},
+			// This test case is commented out because it produces a TypeScript compilation error:
+			// error creating TS program for /tsconfig.json: found 5 syntactic errors. [Invalid character. [\r\n\t/* comment */,\n// comment\n ,]; Invalid character. [\r\n\t/* comment */,\n// comment\n ,]; Invalid character. [\r\n\t/* comment */,\n// comment\n ,]; Invalid character. [\r\n\t/* comment */,\n// comment\n ,]; ']' expected. [\r\n\t/* comment */,\n// comment\n ,];]
+			//{
+			//	Code: `[\r\n\t/* comment */,\n// comment\n ,];`,
+			//	Errors: []rule_tester.InvalidTestCaseError{
+			//		{MessageId: "unexpectedSparseArray", Line: 1, Column: 9},
+			//	},
+			//},
+			{
+				Code: `[(( [a,] )),,,];`,
+				Errors: []rule_tester.InvalidTestCaseError{
+					{MessageId: "unexpectedSparseArray", Line: 1, Column: 1},
+					{MessageId: "unexpectedSparseArray", Line: 1, Column: 1},
+				},
+			},
+			{
+				Code: `[,(( [a,] )),,];`,
+				Errors: []rule_tester.InvalidTestCaseError{
+					{MessageId: "unexpectedSparseArray", Line: 1, Column: 1},
+					{MessageId: "unexpectedSparseArray", Line: 1, Column: 1},
+				},
+			},
+		},
+	)
+}