fix corner case in `collapse_vars` (#4217)

fixes #4216

3 files changed, 25 insertions, 4 deletions

diff --git a/lib/compress.js b/lib/compress.js
index baa501ff..b2ed17cf 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1501,9 +1501,9 @@ merge(Compressor.prototype, {
                 // Skip (non-executed) functions
                 if (node instanceof AST_Scope) return node;
                 // Stop upon collision with block-scoped variables
-                if (node.variables && !node.variables.all(function(def) {
+                if (!(node.variables && node.variables.all(function(def) {
                     return !lvalues.has(def.name);
-                })) {
+                }))) {
                     abort = true;
                     return node;
                 }
diff --git a/lib/output.js b/lib/output.js
index 05baa239..7077d6dd 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -1385,8 +1385,6 @@ function OutputStream(options) {
             make_block(stat, output);
         } else if (!stat || stat instanceof AST_EmptyStatement) {
             output.force_semicolon();
-        } else if (stat instanceof AST_Const) {
-            make_block(stat, output);
         } else {
             stat.print(output);
         }
diff --git a/test/compress/const.js b/test/compress/const.js
index 4411cbf8..27c55ddb 100644
--- a/test/compress/const.js
+++ b/test/compress/const.js
@@ -1009,3 +1009,26 @@ issue_4212_2: {
     }
     expect_stdout: true
 }
+
+issue_4216: {
+    options = {
+        collapse_vars: true,
+        conditionals: true,
+        dead_code: true,
+        evaluate: true,
+    }
+    input: {
+        if (a = 0) {
+            const a = 0;
+        }
+        console.log(typeof a);
+    }
+    expect: {
+        a = 0;
+        {
+            const a = void 0;
+        }
+        console.log(typeof a);
+    }
+    expect_stdout: true
+}