fix empty statement with label

lib/compress.js

@@ -2395,7 +2395,7 @@ merge(Compressor.prototype, {
             if (compressor.option("dead_code") && self instanceof AST_While) {
                 var a = [];
                 extract_declarations_from_unreachable_code(compressor, self.body, a);
-                return make_node(AST_BlockStatement, self, { body: a });
+                return make_node(AST_BlockStatement, self, { body: a }).optimize(compressor);
             }
             if (self instanceof AST_Do) {
                 var has_loop_control = false;
@@ -2475,7 +2475,7 @@ merge(Compressor.prototype, {
                     }));
                 }
                 extract_declarations_from_unreachable_code(compressor, self.body, a);
-                return make_node(AST_BlockStatement, self, { body: a });
+                return make_node(AST_BlockStatement, self, { body: a }).optimize(compressor);
             }
             if (cond !== self.condition) {
                 cond = make_node_from_constant(cond, self.condition).transform(compressor);
@@ -2727,9 +2727,9 @@ merge(Compressor.prototype, {
             var body = [];
             if (self.bcatch) extract_declarations_from_unreachable_code(compressor, self.bcatch, body);
             if (self.bfinally) body = body.concat(self.bfinally.body);
-            return body.length > 0 ? make_node(AST_BlockStatement, self, {
+            return make_node(AST_BlockStatement, self, {
                 body: body
-            }).optimize(compressor) : make_node(AST_EmptyStatement, self);
+            }).optimize(compressor);
         }
         return self;
     });

lib/output.js

@@ -190,11 +190,7 @@ function OutputStream(options) {
     var might_need_space = false;
     var might_need_semicolon = false;
     var might_add_newline = 0;
-    var last = null;
+    var last = "";
-
-    function last_char() {
-        return last.charAt(last.length - 1);
-    };
 
     var ensure_line_len = options.max_line_len ? function() {
         if (current_col > options.max_line_len) {
@@ -218,10 +214,11 @@ function OutputStream(options) {
     function print(str) {
         str = String(str);
         var ch = str.charAt(0);
+        var prev = last.charAt(last.length - 1);
         if (might_need_semicolon) {
             might_need_semicolon = false;
 
-            if ((!ch || ";}".indexOf(ch) < 0) && !/[;]$/.test(last)) {
+            if (prev == ":" && ch == "}" || (!ch || ";}".indexOf(ch) < 0) && prev != ";") {
                 if (options.semicolons || requireSemicolonChars(ch)) {
                     OUTPUT += ";";
                     current_col++;
@@ -258,7 +255,6 @@ function OutputStream(options) {
         }
 
         if (might_need_space) {
-            var prev = last_char();
             if ((is_identifier_char(prev)
                     && (is_identifier_char(ch) || ch == "\\"))
                 || (ch == "/" && ch == prev)

test/compress/issue-1833.js

@@ -118,3 +118,17 @@ label_do: {
         } while (0);
     }
 }
+
+label_while: {
+    options = {
+        evaluate: true,
+        dead_code: true,
+        loops: true,
+    }
+    input: {
+        function f() {
+            L: while (0) continue L;
+        }
+    }
+    expect_exact: "function f(){L:;}"
+}