fix: incorrect to_simple_statement

lib/compress/tighten-body.js

@@ -1236,7 +1236,7 @@ export function tighten_body(statements, compressor) {
             var line = block.body[i];
             if (line instanceof AST_Var && declarations_only(line)) {
                 decls.push(line);
-            } else if (stat) {
+            } else if (stat || line instanceof AST_Const || line instanceof AST_Let) {
                 return false;
             } else {
                 stat = line;

test/compress/issue-1248.js

@@ -0,0 +1,67 @@
+brackets_with_const: {
+    options = {
+        defaults: false,
+    };
+    input: {
+        if (a) {
+            var b;
+            var c;
+            const d = d();
+            const e = e();
+        }
+    }
+    expect: {
+        if(a){var b;var c;const d=d();const e=e()}
+    }
+}
+
+brackets_with_const_defaults: {
+    options = {
+        defaults: true,
+    };
+    input: {
+        if (a) {
+            var b;
+            var c;
+            const d = d();
+            const e = e();
+        }
+    }
+    expect: {
+        if(a){var b,c;const d=d(),e=e()}
+    }
+}
+
+brackets_with_const_let_mix_0: {
+    options = {
+        defaults: true,
+    };
+    input: {
+        if (a) {
+            var b;
+            var c;
+            const d = d();
+            let e = e();
+        }
+    }
+    expect: {
+        if(a){var b,c;const d=d();let e=e()}
+    }
+}
+
+brackets_with_const_let_mix_1: {
+    options = {
+        defaults: true,
+    };
+    input: {
+        if (a) {
+            let b = b();
+            var c;
+            var d;
+            const e = e();
+        }
+    }
+    expect: {
+        if(a){let b=b();var c,d;const e=e()}
+    }
+}