[PATCH] D145783: Reserve unused bits in struct CXIndexOptions; NFC

[Igor Kushnir via Phabricator via cfe-commits]

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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D145783

Files:
  clang/include/clang-c/Index.h
  clang/tools/libclang/CIndex.cpp


Index: clang/tools/libclang/CIndex.cpp
===================================================================
--- clang/tools/libclang/CIndex.cpp
+++ clang/tools/libclang/CIndex.cpp
@@ -3724,6 +3724,13 @@
   // if (options->Size >= offsetof(CXIndexOptions, RecentlyAddedMember))
   //   do_something(options->RecentlyAddedMember);
 
+  // An exception: if a new option is small enough, it can be squeezed into the
+  // /*Reserved*/ bits in CXIndexOptions. Since the default value of each option
+  // is guaranteed to be 0 and the callers are advised to zero out the struct,
+  // programs built against older libclang versions would implicitly set the new
+  // options to default values, which should keep the behavior of previous
+  // libclang versions and thus be backward-compatible.
+
   // If options->Size > sizeof(CXIndexOptions), the user may have set an option
   // we can't handle, in which case we return nullptr to report failure.
   // Replace `!=` with `>` here to support older struct versions. `!=` has the
Index: clang/include/clang-c/Index.h
===================================================================
--- clang/include/clang-c/Index.h
+++ clang/include/clang-c/Index.h
@@ -367,6 +367,7 @@
    * \see clang_createIndex()
    */
   unsigned DisplayDiagnostics : 1;
+  unsigned /*Reserved*/ : 14;
   /**
    * The path to a directory, in which to store temporary PCH files. If null or
    * empty, the default system temporary directory is used. These PCH files are


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