gn build: Make sync script group output by revision

[thakis]

defaultdict

[pcc]

LGTM

llvm/utils/gn/build/sync_source_lists_from_cmake.py

gn_files = subprocess.check_output(['git', 'ls-files', '*BUILD.gn'],
                                        shell=os.name == 'nt').splitlines()
 
     # Matches e.g. |   "foo.cpp",|, captures |foo| in group 1.
     gn_cpp_re = re.compile(r'^\s*"([^"]+\.(?:cpp|c|h|S))",$', re.MULTILINE)
     # Matches e.g. |   foo.cpp|, captures |foo| in group 1.
     cmake_cpp_re = re.compile(r'^\s*([A-Za-z_0-9./-]+\.(?:cpp|c|h|S))$',
                               re.MULTILINE)
 
-    changed = False
+    changes_by_rev = {}
+
+    def find_gitrev(touched_line, in_file):
+        return subprocess.check_output(
+            ['git', 'log', '--format=%h', '-1', '-S' + touched_line, in_file],
+            shell=os.name == 'nt').rstrip()
+    def svnrev_from_gitrev(gitrev):
+        git_llvm = os.path.join(
+            os.path.dirname(__file__), '..', '..', 'git-svn', 'git-llvm')
+        return int(subprocess.check_output(
+            [sys.executable, git_llvm, 'svn-lookup', gitrev],
+            shell=os.name == 'nt').rstrip().lstrip('r'))
+
+    # Collect changes to gn files, grouped by revision.
     for gn_file in gn_files:
         # The CMakeLists.txt for llvm/utils/gn/secondary/foo/BUILD.gn is
-        # directly at foo/CMakeLists.txt.
+        # at foo/CMakeLists.txt.
         strip_prefix = 'llvm/utils/gn/secondary/'
         if not gn_file.startswith(strip_prefix):
             continue
         cmake_file = os.path.join(
                 os.path.dirname(gn_file[len(strip_prefix):]), 'CMakeLists.txt')
         if not os.path.exists(cmake_file):
             continue
 
         def get_sources(source_re, text):
             return set([m.group(1) for m in source_re.finditer(text)])
         gn_cpp = get_sources(gn_cpp_re, open(gn_file).read())
         cmake_cpp = get_sources(cmake_cpp_re, open(cmake_file).read())
 
         if gn_cpp == cmake_cpp:
             continue
 
-        changed = True
-        print(gn_file)
-        add = sorted(cmake_cpp - gn_cpp)
+        def by_rev(files, key):
+            for f in files:
+                svnrev = svnrev_from_gitrev(find_gitrev(f, cmake_file))
+                changes_by_rev.setdefault(svnrev, {})\
+                    .setdefault(gn_file, {}).setdefault(key, []).append(f)
+        by_rev(sorted(cmake_cpp - gn_cpp), 'add')
+        by_rev(sorted(gn_cpp - cmake_cpp), 'remove')
+
+    # Output necessary changes grouped by revision.
+    for svnrev in sorted(changes_by_rev.keys()):
+        print('gn build: Merge r{0} -- https://reviews.llvm.org/rL{0}'
+            .format(svnrev))
+        for gn_file, data in sorted(changes_by_rev[svnrev].items()):
+            print('  ' + gn_file)
+            add = data.get('add')
             if add:
-            print('add:\n' + '\n'.join('    "%s",' % a for a in add))
-        remove = sorted(gn_cpp - cmake_cpp)
+                print('    add:\n' + '\n'.join('    "%s",' % a for a in add))
+            remove = data.get('remove')
             if remove:
-            print('remove:\n' + '\n'.join(remove))
+                print('    remove:\n    ' + '\n    '.join(remove))
             print()
-    return changed
+        print()
+
+    return bool(changes_by_rev)
 
 
 def sync_unittests():
     # Matches e.g. |add_llvm_unittest_with_input_files|.
     unittest_re = re.compile(r'^add_\S+_unittest', re.MULTILINE)
 
     checked = [ 'clang', 'clang-tools-extra', 'lld', 'llvm' ]
     changed = False