From a3217165c6d2ef7caf58665eb0a61c64ab229b9f Mon Sep 17 00:00:00 2001
From: Daniel Dunbar <daniel@zuster.org>
Date: Mon, 12 Dec 2011 22:45:35 +0000
Subject: [PATCH] llvm-build: Add sketchy support for preserving comments when
 using --write-llvmbuild.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146434 91177308-0d34-0410-b5e6-96231b3b80d8
---
 docs/CommandGuide/llvm-build.pod            |  5 ++++-
 utils/llvm-build/llvmbuild/componentinfo.py |  4 ++++
 utils/llvm-build/llvmbuild/main.py          | 24 +++++++++++++++++++--
 3 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/docs/CommandGuide/llvm-build.pod b/docs/CommandGuide/llvm-build.pod
index 78648ba71e8..14e08cb6299 100644
--- a/docs/CommandGuide/llvm-build.pod
+++ b/docs/CommandGuide/llvm-build.pod
@@ -46,7 +46,10 @@ component combinations.
 =item B<--write-llvmbuild>
 
 Write out new I<LLVMBuild.txt> files based on the loaded components. This is
-useful for auto-upgrading the schema of the files.
+useful for auto-upgrading the schema of the files. B<llvm-build> will try to a
+limited extent to preserve the comments which were written in the original
+source file, although at this time it only preserves block comments that preceed
+the section names in the I<LLVMBuild> files.
 
 =item B<--write-cmake-fragment>
 
diff --git a/utils/llvm-build/llvmbuild/componentinfo.py b/utils/llvm-build/llvmbuild/componentinfo.py
index 079102f676a..e9ef973d08a 100644
--- a/utils/llvm-build/llvmbuild/componentinfo.py
+++ b/utils/llvm-build/llvmbuild/componentinfo.py
@@ -42,6 +42,9 @@ class ComponentInfo(object):
         self.parent_instance = None
         self.children = []
 
+        # The original source path.
+        self._source_path = None
+
     def set_parent_instance(self, parent):
         assert parent.name == self.parent, "Unexpected parent!"
         self.parent_instance = parent
@@ -407,4 +410,5 @@ def load_from_path(path, subpath):
             fatal("unable to load component %r in %r: %s" % (
                     section, path, e.message))
 
+        info._source_path = path
         yield info
diff --git a/utils/llvm-build/llvmbuild/main.py b/utils/llvm-build/llvmbuild/main.py
index 4c14f46c80a..71e11d79cff 100644
--- a/utils/llvm-build/llvmbuild/main.py
+++ b/utils/llvm-build/llvmbuild/main.py
@@ -1,3 +1,4 @@
+import StringIO
 import os
 import sys
 
@@ -231,7 +232,22 @@ class LLVMProjectInfo(object):
             if not os.path.exists(directory_path):
                 os.makedirs(directory_path)
 
-            # Create the LLVMBuild file.
+            # In an effort to preserve comments (which aren't parsed), read in
+            # the original file and extract the comments. We only know how to
+            # associate comments that prefix a section name.
+            f = open(infos[0]._source_path)
+            comments_map = {}
+            comment_block = ""
+            for ln in f:
+                if ln.startswith(';'):
+                    comment_block += ln
+                elif ln.startswith('[') and ln.endswith(']\n'):
+                    comments_map[ln[:-1]] = comment_block
+                else:
+                    comment_block = ""
+            f.close()
+
+            # Create the LLVMBuild fil[e.
             file_path = os.path.join(directory_path, 'LLVMBuild.txt')
             f = open(file_path, "w")
 
@@ -260,7 +276,11 @@ class LLVMProjectInfo(object):
 """ % header_string
 
             for i,fragment in enumerate(fragments):
-                print >>f, '[component_%d]' % i
+                name = '[component_%d]' % i
+                comment = comments_map.get(name)
+                if comment is not None:
+                    f.write(comment)
+                print >>f, name
                 f.write(fragment)
                 if fragment is not fragments[-1]:
                     print >>f
-- 
2.34.1