fix: avoid empty block for unused statement

Author: hai-x

lib/ConstPlugin.js

@@ -180,7 +180,7 @@ class ConstPlugin {
 								? statement.alternate
 								: statement.consequent;
 							if (branchToRemove) {
-								this.eliminateUnusedStatement(parser, branchToRemove);
+								this.eliminateUnusedStatement(parser, branchToRemove, true);
 							}
 							return bool;
 						}
@@ -193,7 +193,7 @@ class ConstPlugin {
 						) {
 							return;
 						}
-						this.eliminateUnusedStatement(parser, statement);
+						this.eliminateUnusedStatement(parser, statement, false);
 						return true;
 					});
 					parser.hooks.expressionConditionalOperator.tap(
@@ -509,9 +509,10 @@ class ConstPlugin {
 	 * Eliminate an unused statement.
 	 * @param {JavascriptParser} parser the parser
 	 * @param {Statement} statement the statement to remove
+	 * @param {boolean} alwaysInBlock whether to always generate curly brackets
 	 * @returns {void}
 	 */
-	eliminateUnusedStatement(parser, statement) {
+	eliminateUnusedStatement(parser, statement, alwaysInBlock) {
 		// Before removing the unused branch, the hoisted declarations
 		// must be collected.
 		//
@@ -545,8 +546,14 @@ class ConstPlugin {
 		const declarations = parser.scope.isStrict
 			? getHoistedDeclarations(statement, false)
 			: getHoistedDeclarations(statement, true);
-		const replacement =
-			declarations.length > 0 ? `{ var ${declarations.join(", ")}; }` : "{}";
+
+		const inBlock = alwaysInBlock || statement.type === "BlockStatement";
+
+		let replacement = inBlock ? "{" : "";
+		replacement +=
+			declarations.length > 0 ? ` var ${declarations.join(", ")}; ` : "";
+		replacement += inBlock ? "}" : "";
+
 		const dep = new ConstDependency(
 			`// removed by dead control flow\n${replacement}`,
 			/** @type {Range} */ (statement.range)