Add --prefetch flag for deps prefetch without running (#1475)

tools/prefetch_test.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+# Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import os
+import sys
+from util import tests_path, run_output, build_path, executable_suffix, green_ok
+import tempfile
+import shutil
+
+
+def prefetch_test(deno_exe):
+    sys.stdout.write("prefetch_test...")
+    sys.stdout.flush()
+
+    # On Windows, set the base directory that mkdtemp() uses explicitly. If not,
+    # it'll use the short (8.3) path to the temp dir, which triggers the error
+    # 'TS5009: Cannot find the common subdirectory path for the input files.'
+    temp_dir = os.environ["TEMP"] if os.name == 'nt' else None
+    deno_dir = tempfile.mkdtemp(dir=temp_dir)
+    try:
+        t = os.path.join(tests_path, "006_url_imports.ts")
+        output = run_output([deno_exe, "--prefetch", t],
+                            merge_env={"DENO_DIR": deno_dir})
+        assert output == ""
+        # Check that we actually did the prefetch.
+        os.path.exists(
+            os.path.join(deno_dir,
+                         "deps/http/localhost_PORT4545/tests/subdir/mod2.ts"))
+    finally:
+        shutil.rmtree(deno_dir)
+
+    print green_ok()
+
+
+if __name__ == "__main__":
+    prefetch_test(sys.argv[1])