feat: implement no-sparse-arrays (#411)

Author: Thiry1

internal/config/config.go

@@ -96,6 +96,7 @@ 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
@@ -461,6 +462,7 @@ 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)

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.",
+						})
+					}
+				}
+			},
+		}
+	},
+}

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},
+				},
+			},
+		},
+	)
+}