scripts: Use glslang sha for SPIRV_TOOLS_COMMIT_ID

Fix awkward depencency between any change to known_good.json and
spirv_tools_commit_id.h. Now generated spirv_tools_commit_id.h will
only change when glslang commit id in known_good.json changes.

Change-Id: Id4c7bfde061509426eea0660ef18c7ff069f1409
diff --git a/scripts/external_revision_generator.py b/scripts/external_revision_generator.py
index 6edb973..497291a 100644
--- a/scripts/external_revision_generator.py
+++ b/scripts/external_revision_generator.py
@@ -24,6 +24,7 @@
 import hashlib
 import subprocess
 import uuid
+import json
 
 def generate(symbol_name, commit_id, output_header_file):
     # Write commit ID to output header file
@@ -85,21 +86,36 @@
         return sha1.hexdigest()
 
 def get_commit_id_from_uuid():
-        unique_uuid = str(uuid.uuid4())
-        sha1 = hashlib.sha1();
-        sha1.update(unique_uuid.encode())
-        return sha1.hexdigest()
+    unique_uuid = str(uuid.uuid4())
+    sha1 = hashlib.sha1();
+    sha1.update(unique_uuid.encode())
+    return sha1.hexdigest()
+
+def get_commit_id_from_json(json_file, json_keys):
+    with open(json_file) as json_stream:
+        json_data = json.load(json_stream)
+    for key in json_keys.split(','):
+        if type(json_data) == list:
+            json_data = json_data[int(key)]
+        else:
+            json_data = json_data[key]
+    return json_data
 
 def main():
     parser = argparse.ArgumentParser()
-    parser.add_argument("-s", "--symbol_name", metavar="SYMBOL_NAME", required=True, help="C symbol name")
-    parser.add_argument("-o", "--output_header_file", metavar="OUTPUT_HEADER_FILE", required=True, help="output header file path")
     rev_method_group = parser.add_mutually_exclusive_group(required=True)
     rev_method_group.add_argument("--git_dir", metavar="SOURCE_DIR", help="git working copy directory")
     rev_method_group.add_argument("--rev_file", metavar="REVISION_FILE", help="source revision file path (must contain a SHA1 hash")
     rev_method_group.add_argument("--from_uuid", action='store_true', help="base SHA1 on a dynamically generated UUID")
+    rev_method_group.add_argument("--json_file", metavar="JSON_FILE", help="path to json file")
+    parser.add_argument("-s", "--symbol_name", metavar="SYMBOL_NAME", required=True, help="C symbol name")
+    parser.add_argument("-o", "--output_header_file", metavar="OUTPUT_HEADER_FILE", required=True, help="output header file path")
+    parser.add_argument("--json_keys", action='store', metavar="JSON_KEYS", help="comma-separated list of keys specifying SHA1 location in root json object for --json_file option")
     args = parser.parse_args()
 
+    if ('json_file' in args) != ('json_keys' in args):
+        parser.error('--json_file and --json_keys must be provided together')
+
     # We can either parse the latest Git commit ID out of the specified repository (preferred where possible),
     # or computing the SHA1 hash of the contents of a file passed on the command line and (where necessary --
     # e.g. when building the layers outside of a Git environment).
@@ -113,7 +129,9 @@
     elif args.rev_file is not None:
         # Read the commit ID from a file.
         commit_id = get_commit_id_from_file(args.rev_file)
-    elif args.from_uuid is not None:
+    elif args.json_file is not None:
+        commit_id = get_commit_id_from_json(args.json_file, args.json_keys)
+    elif args.from_uuid:
         commit_id = get_commit_id_from_uuid()
 
     if not is_sha1(commit_id):