r194250 - clang-format: Write files atomically

Alp Toker alp at nuanti.com
Fri Nov 8 00:07:19 PST 2013

Author: alp
Date: Fri Nov  8 02:07:19 2013
New Revision: 194250

URL: http://llvm.org/viewvc/llvm-project?rev=194250&view=rev
clang-format: Write files atomically

Switch clang-format over to Rewriter::overwriteChangedFiles().

The previous implementation was attempting to stream back directly to the
original file and failing if it was already memory mapped by MemoryBuffer,
an operation unsupported by Windows.

MemoryBuffer generally mmaps files larger than the physical page size so
this will have been difficult to reproduce consistently.

This change also reduces flicker in code editors and IDEs on all platforms
when reformatting in-place.

Note that other incorrect uses of MemoryBuffer exist in LLVM/clang and
will need a similar fix.

A test should be added for Windows when libFormat performance issues are
fixed (it takes longer than a day to format a 1MB file at present!)


Modified: cfe/trunk/tools/clang-format/ClangFormat.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/tools/clang-format/ClangFormat.cpp?rev=194250&r1=194249&r2=194250&view=diff
--- cfe/trunk/tools/clang-format/ClangFormat.cpp (original)
+++ cfe/trunk/tools/clang-format/ClangFormat.cpp Fri Nov  8 02:07:19 2013
@@ -213,18 +213,8 @@ static bool format(std::string FileName)
     Rewriter Rewrite(Sources, LangOptions());
     tooling::applyAllReplacements(Replaces, Rewrite);
     if (Inplace) {
-      if (Replaces.size() == 0)
-        return false; // Nothing changed, don't touch the file.
-      std::string ErrorInfo;
-      llvm::raw_fd_ostream FileStream(FileName.c_str(), ErrorInfo,
-                                      llvm::sys::fs::F_Binary);
-      if (!ErrorInfo.empty()) {
-        llvm::errs() << "Error while writing file: " << ErrorInfo << "\n";
+      if (Rewrite.overwriteChangedFiles())
         return true;
-      }
-      Rewrite.getEditBuffer(ID).write(FileStream);
-      FileStream.flush();
     } else {
       if (Cursor.getNumOccurrences() != 0)
         outs() << "{ \"Cursor\": " << tooling::shiftedCodePosition(

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