reject non-toplevel import/export (#2128)

fixes #2124

lib/scope.js

@@ -223,6 +223,15 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
             }));
             node.thedef = sym;
         }
+        if (!(scope instanceof AST_Toplevel) && (node instanceof AST_Export || node instanceof AST_Import)) {
+            js_error(
+                node.TYPE + " statement may only appear at top level",
+                node.start.file,
+                node.start.line,
+                node.start.col,
+                node.start.pos
+            );
+        }
 
         function mark_export(def, level) {
             var node = tw.parent(level);

test/compress/export.js

@@ -40,34 +40,6 @@ issue_2038_2: {
     }
 }
 
-issue_2124: {
-    options = {
-        unused: true,
-    }
-    input: {
-        {
-            export var V = 1;
-        }
-        {
-            export let L = 2;
-        }
-        {
-            export const C = 3;
-        }
-    }
-    expect: {
-        {
-            export var V = 1;
-        }
-        {
-            export let L = 2;
-        }
-        {
-            export const C = 3;
-        }
-    }
-}
-
 issue_2126: {
     mangle = {
         toplevel: true,

test/input/invalid/export.js

@@ -0,0 +1,3 @@
+{
+    export var V = 1;
+}

test/input/invalid/import.js

@@ -0,0 +1,3 @@
+{
+    import A from "B";
+}

test/mocha/cli.js

@@ -533,6 +533,36 @@ describe("bin/uglifyjs", function () {
             done();
         });
     });
+    it("Should throw syntax error (block-level export)", function(done) {
+        var command = uglifyjscmd + ' test/input/invalid/export.js -m';
+
+        exec(command, function (err, stdout, stderr) {
+            assert.ok(err);
+            assert.strictEqual(stdout, "");
+            assert.strictEqual(stderr.split(/\n/).slice(0, 4).join("\n"), [
+                "Parse error at test/input/invalid/export.js:2,4",
+                "    export var V = 1;",
+                "    ^",
+                "ERROR: Export statement may only appear at top level"
+            ].join("\n"));
+            done();
+        });
+    });
+    it("Should throw syntax error (block-level import)", function(done) {
+        var command = uglifyjscmd + ' test/input/invalid/import.js -m';
+
+        exec(command, function (err, stdout, stderr) {
+            assert.ok(err);
+            assert.strictEqual(stdout, "");
+            assert.strictEqual(stderr.split(/\n/).slice(0, 4).join("\n"), [
+                "Parse error at test/input/invalid/import.js:2,4",
+                '    import A from "B";',
+                "    ^",
+                "ERROR: Import statement may only appear at top level"
+            ].join("\n"));
+            done();
+        });
+    });
     it("Should handle literal string as source map input", function(done) {
         var command = [
             uglifyjscmd,