parse export & import statements correctly (#5550)

fixes #5548

test/mocha/exports.js

@@ -68,4 +68,64 @@ describe("export", function() {
             }, code);
         });
     });
+    it("Should reject `export` statement not under top-level scope", function() {
+        [
+            "{ export {}; }",
+            "if (0) export var A;",
+            "function f() { export default 42; }",
+        ].forEach(function(code) {
+            assert.throws(function() {
+                UglifyJS.parse(code);
+            }, function(e) {
+                return e instanceof UglifyJS.JS_Parse_Error;
+            }, code);
+        });
+    });
+    it("Should compare `export` statements correctly", function() {
+        var stats = {
+            Declaration: [
+                "export let A;",
+                "export const A = 42;",
+                "export var { A, B: [] } = C;",
+                "export function A() { return B(A); }",
+                "export async function* A({}, ...[]) { return B(A); }",
+            ],
+            Default: [
+                "export default 42;",
+                "export default A => A(B);",
+                "export default class A extends B {}",
+                "export default (class A extends B {});",
+                "export default class A { static C = 42; }",
+                "export default class A extends B { static C = 42; }",
+            ],
+            Foreign: [
+                "export * from 'path';",
+                "export {} from 'path';",
+                "export * as A from 'path';",
+                "export { default } from 'path';",
+                "export { A, B as C } from 'path';",
+                "export { A, default as C } from 'path';",
+            ],
+            References: [
+                "export {};",
+                "export { A };",
+                "export { A as B };",
+                "export { A, B as C };",
+                "export { A as default };",
+            ],
+        };
+        for (var k in stats) stats[k].forEach(function(c, i) {
+            var s = UglifyJS.parse(c);
+            assert.ok(s instanceof UglifyJS.AST_Toplevel, c);
+            assert.strictEqual(s.body.length, 1, c);
+            assert.strictEqual(s.body[0].TYPE, "Export" + k, c);
+            for (var l in stats) stats[l].forEach(function(d, j) {
+                var t = UglifyJS.parse(d);
+                assert.ok(t instanceof UglifyJS.AST_Toplevel, d);
+                assert.strictEqual(t.body.length, 1, d);
+                assert.strictEqual(t.body[0].TYPE, "Export" + l, d);
+                assert.strictEqual(s.equals(t), k === l && i === j, c + "\n" + d);
+            });
+        });
+    });
 });