[gen_ast_dump_json_test.py] Infer --filters flags when using --update

See https://reviews.llvm.org/D70119

Author: arichardson

clang/test/AST/gen_ast_dump_json_test.py

@@ -68,7 +68,6 @@ def main():
     update_or_generate_group.add_argument("--update", help="Update the file in-place", action="store_true")
     update_or_generate_group.add_argument("--opts", help="other options",
                                           action="store", default='', type=str)
-
     args = parser.parse_args()
 
     if not args.source:
@@ -80,19 +79,31 @@ def main():
         print("clang binary specified not present.")
         return -1
 
-    filters = set(args.filters.split(',')) if args.filters else set()
-    
-    note = "// NOTE: CHECK lines have been autogenerated by " \
-           "gen_ast_dump_json_test.py"
-           
-    if (args.filters):
-        note += "\n// using --filters=" + args.filters
-    
+    note_firstline = "// NOTE: CHECK lines have been autogenerated by " \
+                     "gen_ast_dump_json_test.py"
+    filters_line_prefix = "// using --filters="
+    note = note_firstline
+
     cmd = [clang_binary, "-cc1"]
     if args.update:
         # When updating the first line of the test must be a RUN: line
         with open(args.source, "r") as srcf:
             first_line = srcf.readline()
+            filters_line_next = False
+            filters_line = None
+            for i, line in enumerate(srcf.readlines()):
+                if filters_line_next:
+                    # print("Filters line: '", line.rstrip(), "'", sep="")
+                    if line.startswith(filters_line_prefix):
+                        filters_line = line[len(filters_line_prefix):].rstrip()
+                    break
+                if line.startswith(note_firstline):
+                    filters_line_next = True
+                    # print("Found autogenerated disclaimer at line", i + 1)
+        if not args.filters and filters_line:
+            args.filters = filters_line
+            print("Inferred filters as '" + args.filters + "'")
+
         if "RUN: %clang_cc1 " not in first_line:
             sys.exit("When using --update the first line of the input file must contain RUN: %clang_cc1")
         clang_start = first_line.find("%clang_cc1") + len("%clang_cc1")
@@ -115,6 +126,12 @@ def main():
     using_ast_dump_filter = any('ast-dump-filter' in arg for arg in cmd)
     cmd.append(args.source)
     print("Will run", cmd)
+    filters = set()
+    if args.filters:
+        note += "\n" + filters_line_prefix + args.filters
+        filters = set(args.filters.split(','))
+    print("Will use the following filters:", filters)
+
 
     try:
         json_str = subprocess.check_output(cmd)
@@ -147,7 +164,7 @@ def main():
         with open(args.source, "r") as srcf:
             for line in srcf.readlines():
                 # copy up to the note:
-                if line.rstrip() == note:
+                if line.rstrip() == note_firstline:
                     break
                 f.write(line)
         f.write(note + "\n")