Frontend: Sink named pipe logic from CompilerInstance down to FileManager

[dexonsmith]

Summary

Remove compilicated logic from CompilerInstance::InitializeSourceManager
to deal with named pipes, updating FileManager::getBufferForFile to
handle it in a more straightforward way. The existing test at
clang/test/Misc/dev-fd-fs.c covers the new behaviour.

[dexonsmith]

ping

[dexonsmith]

ping

[jansvoboda11]

LGTM

[dexonsmith]

Hmm, I had to revert this in b34632201987eed369bb7ef4646f341b901c95b8 due to a bot failure; I'll need to look into it.

[dexonsmith]

In D90733#2429976, @dexonsmith wrote:

Hmm, I had to revert this in b34632201987eed369bb7ef4646f341b901c95b8 due to a bot failure; I'll need to look into it.

Posted a new version here: https://reviews.llvm.org/D92531

clang/lib/Basic/FileManager.cpp

 }
 
 llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
 FileManager::getBufferForFile(const FileEntry *Entry, bool isVolatile,
                               bool RequiresNullTerminator) {
   uint64_t FileSize = Entry->getSize();
   // If there's a high enough chance that the file have changed since we
   // got its size, force a stat before opening it.
-  if (isVolatile)
+  if (isVolatile || Entry->isNamedPipe())
     FileSize = -1;
 
   StringRef Filename = Entry->getName();
   // If the file is already open, use the open file descriptor.
   if (Entry->File) {
     auto Result = Entry->File->getBuffer(Filename, FileSize,
                                          RequiresNullTerminator, isVolatile);
     Entry->closeFile();

clang/lib/Frontend/CompilerInstance.cpp

if (InputFile != "-") {
     if (!FileOrErr) {
       // FIXME: include the error in the diagnostic.
       consumeError(FileOrErr.takeError());
       Diags.Report(diag::err_fe_error_reading) << InputFile;
       return false;
     }
     FileEntryRef File = *FileOrErr;
 
-    // The natural SourceManager infrastructure can't currently handle named
-    // pipes, but we would at least like to accept them for the main
-    // file. Detect them here, read them with the volatile flag so FileMgr will
-    // pick up the correct size, and simply override their contents as we do for
-    // STDIN.
-    if (File.getFileEntry().isNamedPipe()) {
-      auto MB =
-          FileMgr.getBufferForFile(&File.getFileEntry(), /*isVolatile=*/true);
-      if (MB) {
-        // Create a new virtual file that will have the correct size.
-        const FileEntry *FE =
-            FileMgr.getVirtualFile(InputFile, (*MB)->getBufferSize(), 0);
-        SourceMgr.overrideFileContents(FE, std::move(*MB));
-        SourceMgr.setMainFileID(
-            SourceMgr.createFileID(FE, SourceLocation(), Kind));
-      } else {
-        Diags.Report(diag::err_cannot_open_file) << InputFile
-                                                 << MB.getError().message();
-        return false;
-      }
-    } else {
-      SourceMgr.setMainFileID(
-          SourceMgr.createFileID(File, SourceLocation(), Kind));
-    }
   } else {
     llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> SBOrErr =
         llvm::MemoryBuffer::getSTDIN();
     if (std::error_code EC = SBOrErr.getError()) {
       Diags.Report(diag::err_fe_error_reading_stdin) << EC.message();
       return false;
     }
     std::unique_ptr<llvm::MemoryBuffer> SB = std::move(SBOrErr.get());