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

[Qiongsi Wu 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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qiongsiwu wrote:

What is the reason that we want to create unique files here? Is it that we are trying to be consistent with what we do in `OnDiskOutputFile::tryToCreateTemporary` (or in general how we write files to disk)? Would it be a good idea to pull out the common utility part and share some code? It might not be that straightforward and I don't think this is a blocker. 

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