[clang] [llvm] [mlir] [support] Use VFS in `SourceMgr` for loading includes (PR #162903)

[Hideto Ueno via llvm-commits]

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@@ -378,8 +378,10 @@ struct SourceMgrDiagnosticHandlerImpl {
     }
 
     // Otherwise, try to load the source file.
-    std::string ignored;
-    unsigned id = mgr.AddIncludeFile(std::string(filename), SMLoc(), ignored);
+    auto bufferOrErr = llvm::MemoryBuffer::getFile(filename);
+    if (!bufferOrErr)
+      return 0;
+    unsigned id = mgr.AddNewSourceBuffer(std::move(*bufferOrErr), SMLoc());
     filenameToBufId[filename] = id;
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uenoku wrote:

Hello! Is this change intentional? It broke a downstream tool ;) I think a new code doesn't search include directories (and also not using VFS as well?). 

https://github.com/llvm/llvm-project/pull/162903