1 files changed, 62 insertions, 16 deletions

diff --git a/tools/setup.py b/tools/setup.py
index 737f80017..77aaf95d6 100755
--- a/tools/setup.py
+++ b/tools/setup.py
@@ -2,6 +2,7 @@
 import third_party
 from util import run, root_path, build_path, build_mode
 import os
+import re
 import sys
 from distutils.spawn import find_executable
 
@@ -44,15 +45,55 @@ def write_lastchange():
     # ])
 
 
-def get_gn_args():
+# If this text is found in args.gn, we assume it hasn't been hand edited.
+gn_args_header = [
+    "# This file is automatically generated by tools/setup.py.",
+    "# REMOVE THIS LINE to preserve any changes you make.", ""
+]
+
+
+def gn_args_are_generated(lines):
+    for line in lines:
+        if re.match("^\s*#.*REMOVE THIS LINE", line):
+            return True
+    return False
+
+
+def read_gn_args(args_filename):
+    if not os.path.exists(args_filename):
+        return (None, False)  # No content, not hand edited.
+
+    with open(args_filename) as f:
+        lines = f.read().splitlines()
+        args = [l.strip() for l in lines if not re.match("^\s*(#|$)", l)]
+        hand_edited = not gn_args_are_generated(lines)
+        return (args, hand_edited)
+
+
+def write_gn_args(args_filename, args):
+    assert not gn_args_are_generated(args)  # No header -> hand crafted.
+    lines = gn_args_header + args
+    assert gn_args_are_generated(lines)  # With header -> generated.
+
+    # Ensure the directory where args.gn goes exists.
+    dir = os.path.dirname(args_filename)
+    if not os.path.isdir(dir):
+        os.makedirs(dir)
+
+    with open(args_filename, "w") as f:
+        f.write("\n".join(lines) + "\n")
+
+
+def generate_gn_args(mode):
     out = []
-    if build_mode() == "release":
+    if mode == "release":
         out += ["is_official_build=true"]
-    elif build_mode() == "debug":
+    elif mode == "debug":
         pass
     else:
-        print "Bad mode {}. Use 'release' or 'debug' (default)" % build_mode()
+        print "Bad mode {}. Use 'release' or 'debug' (default)" % mode
         sys.exit(1)
+
     if "DENO_BUILD_ARGS" in os.environ:
         out += os.environ["DENO_BUILD_ARGS"].split()
 
@@ -67,8 +108,6 @@ def get_gn_args():
             tc = "//build_extra/toolchain/win:win_clang_x64"
             out += ['custom_toolchain="%s"' % tc, 'host_toolchain="%s"' % tc]
 
-    print "DENO_BUILD_ARGS:", out
-
     return out
 
 
@@ -76,20 +115,27 @@ def get_gn_args():
 def gn_gen(mode):
     os.environ["DENO_BUILD_MODE"] = mode
 
-    # mkdir $build_path(). We do this so we can write args.gn before running gn gen.
-    if not os.path.isdir(build_path()):
-        os.makedirs(build_path())
-
-    # Rather than using gn gen --args we manually write the args.gn override file.
+    # Rather than using gn gen --args we write directly to the args.gn file.
     # This is to avoid quoting/escaping complications when passing overrides as
     # command-line arguments.
     args_filename = os.path.join(build_path(), "args.gn")
-    if os.path.exists(args_filename):
-        print "Skip writing args file: '%s' already exists." % args_filename
+
+    # Check if args.gn exists, and if it was auto-generated or handcrafted.
+    existing_gn_args, hand_edited = read_gn_args(args_filename)
+
+    # If args.gn wasn't handcrafted, regenerate it.
+    if hand_edited:
+        print "%s: Using gn options from hand edited '%s'." % (mode,
+                                                               args_filename)
+        gn_args = existing_gn_args
     else:
-        gn_args = get_gn_args()
-        with open(args_filename, "w+") as f:
-            f.write("\n".join(gn_args) + "\n")
+        print "%s: Writing gn options to '%s'." % (mode, args_filename)
+        gn_args = generate_gn_args(mode)
+        if gn_args != existing_gn_args:
+            write_gn_args(args_filename, gn_args)
+
+    for line in gn_args:
+        print "  " + line
 
     run([third_party.gn_path, "gen", build_path()],
         env=third_party.google_env())