[clang] [clang] Introduce `ModuleCache::write()` (PR #188877)

[Jan Svoboda via cfe-commits]

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@@ -101,6 +101,39 @@ void clang::maybePruneImpl(StringRef Path, time_t PruneInterval,
   }
 }
 
+std::error_code clang::writeImpl(StringRef Path, llvm::MemoryBufferRef Buffer) {
+  StringRef Extension = llvm::sys::path::extension(Path);
+  SmallString<128> ModelPath = StringRef(Path).drop_back(Extension.size());
+  ModelPath += "-%%%%%%%%";
+  ModelPath += Extension;
+  ModelPath += ".tmp";
+
+  std::error_code EC;
+  int FD;
+  SmallString<128> TmpPath;
+  if ((EC = llvm::sys::fs::createUniqueFile(ModelPath, FD, TmpPath))) {
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jansvoboda11 wrote:

If we wrote to the final destination directly, readers might observe a partially-written PCM file and erroring out. Renaming a file is atomic, so writing to a temporary file and then renaming the file to the final name is the way to implement atomic file writes.

https://github.com/llvm/llvm-project/pull/188877