gn build: Add get.py script to download prebuilt gn, make gn.py run downloaded gn if gn is not on PATH

Prebuilts are available for x86_64 Linux, macOS, Windows. The script always
pulls the latest GN version.

Differential Revision: https://reviews.llvm.org/D57256

llvm-svn: 352420

1 files changed, 30 insertions, 2 deletions

diff --git a/llvm/utils/gn/gn.py b/llvm/utils/gn/gn.py
index f80873b3be8..f523e6443ea 100755
--- a/llvm/utils/gn/gn.py
+++ b/llvm/utils/gn/gn.py
@@ -15,10 +15,38 @@ THIS_DIR = os.path.dirname(__file__)
 ROOT_DIR = os.path.join(THIS_DIR, '..', '..', '..')
 
 
+def get_platform():
+    if os.uname()[4] != 'x86_64':
+        return None
+    if sys.platform.startswith('linux'):
+        return 'linux-amd64'
+    if sys.platform == 'darwin':
+        return 'mac-amd64'
+    if sys.platform == 'win32':
+        return 'windows-amd64'
+
+
+def print_no_gn(mention_get):
+    print('gn binary not found in PATH')
+    if mention_get:
+        print('run llvm/utils/gn/get.py to download a binary and try again, or')
+    print('follow https://gn.googlesource.com/gn/#getting-started')
+    return 1
+
+
 def main():
-    # Find real gn executable. For now, just assume it's on PATH.
-    # FIXME: Probably need to append '.exe' on Windows.
+    # Find real gn executable.
     gn = 'gn'
+    if subprocess.call([gn, '--version'], stdout=open(os.devnull, 'w'),
+                                          stderr=subprocess.STDOUT) != 0:
+        # Not on path. See if get.py downloaded a prebuilt binary and run that
+        # if it's there, or suggest to run get.py if it isn't.
+        platform = get_platform()
+        if not platform:
+            return print_no_gn(mention_get=False)
+        gn = os.path.join(os.path.dirname(__file__), 'bin', platform, 'gn')
+        if not os.path.exists(gn + ('.exe' if platform == 'windows' else '')):
+            return print_no_gn(mention_get=True)
 
     # Compute --dotfile= and --root= args to add.
     extra_args = []