fix export default of anonymous generators and async functions (#2607)

fixes #2606

test/compress/export.js

@@ -262,3 +262,185 @@ trailing_comma: {
     }
     expect_exact: "export const a = 1;"
 }
+
+export_default_anonymous_function: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default function () {
+            foo();
+        }
+    }
+    expect_exact: "export default function(){foo()};"
+}
+
+export_default_arrow: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default () => foo();
+    }
+    expect_exact: "export default()=>foo();"
+}
+
+export_default_anonymous_generator: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default function * () {
+            yield foo();
+        }
+    }
+    expect_exact: "export default function*(){yield foo()};"
+}
+
+export_default_anonymous_async_function: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default async function() {
+            return await foo();
+        }
+    }
+    expect_exact: "export default async function(){return await foo()};"
+}
+
+export_default_async_arrow_function: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default async () => await foo();
+    }
+    expect_exact: "export default async()=>await foo();"
+}
+
+export_default_named_generator: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default function * gen() {
+            yield foo();
+        }
+    }
+    expect_exact: "export default function*gen(){yield foo()};"
+}
+
+export_default_named_async_function: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default async function bar() {
+            return await foo();
+        }
+    }
+    expect_exact: "export default async function bar(){return await foo()};"
+}
+
+export_default_anonymous_class: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default class {
+            constructor() {
+                foo();
+            }
+        };
+    }
+    expect_exact: "export default class{constructor(){foo()}};"
+}
+
+export_default_anonymous_function_not_call: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default function(){}(foo);
+    }
+    // FIXME: should be `export default function(){};foo;`
+    expect_exact: "export default function(){}(foo);"
+}
+
+export_default_anonymous_generator_not_call: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default function*(){}(foo);
+    }
+    // agrees with `acorn` and `babylon 7`
+    expect_exact: "export default function*(){};foo;"
+}
+
+export_default_anonymous_async_function_not_call: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export default async function(){}(foo);
+    }
+    // agrees with `acorn` and `babylon 7`
+    expect_exact: "export default async function(){};foo;"
+}