Derive the libuast os/arch selector from sys.platform.

Part of the pyuast build process fetches a binary release of libuast.
Previously, the release version was pinned to linux-amd64.

This change makes it consult sys.platform.  Unfortunately, sys.platform doesn't
exactly match the release tag for windows, but since we only have binary
releases for Linux, Darwin, and Windows anyway, it is a straightforward patch.

The default remains linux-amd64 in case someone has another platform; if it was
wrong before it will still be wrong, but in the same way.

Signed-off-by: M. J. Fromberger <michael.j.fromberger@gmail.com>

Author: creachadair

setup.py

@@ -16,7 +16,6 @@
 # You may change the contents of the string, but do not otherwise edit the line.
 VERSION = "3.x.x-dev"
 LIBUAST_VERSION = "v3.3.0"
-LIBUAST_ARCH = "linux-amd64"
 SDK_V1_VERSION = "v1.17.0"
 SDK_V1_MAJOR = SDK_V1_VERSION.split('.')[0]
 SDK_V2_VERSION = "v2.16.4"
@@ -132,6 +131,18 @@ def create_inits(sdk_major):
         open(f, "w").close()
 
 
+def get_libuast_arch():
+    """Return the os-arch tag to use when fetching libuast.
+    """
+
+    # See https://github.com/bblfsh/client-python/issues/156.
+    if sys.platform == 'win32':
+        return 'windows-amd64'
+    elif sys.platform:
+        return sys.platform + '-amd64'
+    return 'linux-amd64'
+
+
 def get_libuast():
     if not GET_LIBUAST:
         return
@@ -141,8 +152,9 @@ def get_libuast():
     mkdir(local_libuast)
 
     # Retrieve libuast
-    untar_url("https://github.com/bblfsh/libuast/releases/download/%s/libuast-%s.tar.gz" % (LIBUAST_VERSION, LIBUAST_ARCH))
-    mv(LIBUAST_ARCH, local_libuast)
+    untar_url("https://github.com/bblfsh/libuast/releases/download/%s/libuast-%s.tar.gz" % (
+        LIBUAST_VERSION, get_libuast_arch()))
+    mv(get_libuast_arch(), local_libuast)
 
 
 def proto_download_v1():