[clang] Auto-detect which newline style to use for cxx_dr_status.html

[Endilll]

Aaron reported that make_cxx_dr_status replaces all newlines in cxx_dr_status.html, which makes for a huge diff. On Windows, we can't be compatible with all autocrlf modes at once, so this patch adds autodetection of newline style using the existing file, if one is present (which should be the case for all reasonable use cases).

[llvmbot]

@llvm/pr-subscribers-clang

Author: Vlad Serebrennikov (Endilll)

Changes

Aaron reported that make_cxx_dr_status replaces all newlines in cxx_dr_status.html, which makes for a huge diff. On Windows, we can't be compatible with all autocrlf modes at once, so this patch adds autodetection of newline style using the existing file, if one is present (which should be the case for all reasonable use cases).

---

Full diff: https://github.com/llvm/llvm-project/pull/132045.diff

1 Files Affected:

• (modified) clang/www/make_cxx_dr_status (+17-1)

diff --git a/clang/www/make_cxx_dr_status b/clang/www/make_cxx_dr_status
index c787bbaff0a36..a4b87b32fc5d8 100755
--- a/clang/www/make_cxx_dr_status
+++ b/clang/www/make_cxx_dr_status
@@ -318,6 +318,22 @@ out_html.append('''\
 </html>
 ''')
 
-out_file = open(output, 'w')
+# Make an effort to remain consistent with the existing file.
+# We can't pick one newline style and use it on Windows,
+# because we can't be compatible with all 'autocrlf' modes at once.
+def detect_newline_style(file_path):
+  if not os.path.exists(file_path):
+    return '\n'
+  f = open(file_path)
+  f.readline()
+  if f.newlines is None:
+    return '\n'
+  if isinstance(f.newlines, str):
+    return f.newlines
+  newline = f.newlines[0]
+  print(f"Existing '{file_path}' has inconsistent newlines; picking '{newline.encode('unicode_escape').decode('utf-8')}'")
+  return newline
+    
+out_file = open(output, 'w', newline=detect_newline_style(output))
 out_file.write(''.join(out_html))
 out_file.close()

[AaronBallman]

LGTM, this works well!