[gjs] build: Handle case where $bindir/gjs symlink already exists

[Philip Chimento <pchimento src gnome org>]

commit a646ef7686906b303362c7a499aac1aa70c48e85
Author: Philip Chimento <philip chimento gmail com>
Date:   Sat Oct 26 16:38:26 2019 -0700

    build: Handle case where $bindir/gjs symlink already exists
    
    Python's os.symlink() will fail if the symlink already exists, so when
    installing GJS in a prefix where it was already installed. This was
    previously avoided with the -f option to ln.
    
    Instead, create a temporary link and atomically rename it over the
    existing link.
    
    Unreviewed, pushing to fix build.

 build/symlink-gjs.py | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/build/symlink-gjs.py b/build/symlink-gjs.py
index 51465e31..365a3211 100644
--- a/build/symlink-gjs.py
+++ b/build/symlink-gjs.py
@@ -4,6 +4,7 @@ import os
 import shutil
 import subprocess
 import sys
+import tempfile
 
 assert(len(sys.argv) == 2)
 
@@ -20,4 +21,10 @@ if os.name == 'nt':
     # which is not what we want.  Instead, copy gjs-console.exe.
     shutil.copyfile('gjs-console.exe', os.path.join(installed_bin_dir, 'gjs.exe'))
 else:
-    os.symlink('gjs-console', os.path.join(installed_bin_dir, 'gjs'))
+    try:
+        temp_link = tempfile.mktemp(dir=installed_bin_dir)
+        os.symlink('gjs-console', temp_link)
+        os.replace(temp_link, os.path.join(installed_bin_dir, 'gjs'))
+    finally:
+        if os.path.islink(temp_link):
+            os.remove(temp_link)