support import statements (#4646)

test/compress/imports.js

@@ -0,0 +1,123 @@
+nought: {
+    input: {
+        import "foo";
+    }
+    expect_exact: 'import"foo";'
+}
+
+default_only: {
+    input: {
+        import foo from "bar";
+    }
+    expect_exact: 'import foo from"bar";'
+}
+
+all_only: {
+    input: {
+        import * as foo from "bar";
+    }
+    expect_exact: 'import*as foo from"bar";'
+}
+
+keys_only: {
+    input: {
+        import { as as foo, bar, delete as baz } from "moo";
+    }
+    expect_exact: 'import{as as foo,bar as bar,delete as baz}from"moo";'
+}
+
+default_all: {
+    input: {
+        import foo, * as bar from "baz";
+    }
+    expect_exact: 'import foo,*as bar from"baz";'
+}
+
+default_keys: {
+    input: {
+        import foo, { bar } from "baz";
+    }
+    expect_exact: 'import foo,{bar as bar}from"baz";'
+}
+
+dynamic: {
+    input: {
+        (async a => await import(a))("foo").then(bar);
+    }
+    expect_exact: '(async a=>await import(a))("foo").then(bar);'
+}
+
+import_meta: {
+    input: {
+        console.log(import.meta, import.meta.url);
+    }
+    expect_exact: "console.log(import.meta,import.meta.url);"
+}
+
+same_quotes: {
+    beautify = {
+        beautify: true,
+        quote_style: 3,
+    }
+    input: {
+        import 'foo';
+        import "bar";
+    }
+    expect_exact: [
+        "import 'foo';",
+        "",
+        'import "bar";',
+    ]
+}
+
+drop_unused: {
+    options = {
+        imports: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        import a, * as b from "foo";
+        import { c, bar as d } from "baz";
+        console.log(c);
+    }
+    expect: {
+        import "foo";
+        import { c as c } from "baz";
+        console.log(c);
+    }
+}
+
+mangle: {
+    rename = false
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        import foo, { bar } from "baz";
+        consoe.log(moo);
+        import * as moo from "moz";
+    }
+    expect: {
+        import o, { bar as m } from "baz";
+        consoe.log(r);
+        import * as r from "moz";
+    }
+}
+
+rename_mangle: {
+    rename = true
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        import foo, { bar } from "baz";
+        consoe.log(moo);
+        import * as moo from "moz";
+    }
+    expect: {
+        import o, { bar as m } from "baz";
+        consoe.log(r);
+        import * as r from "moz";
+    }
+}