[CodeComplete] Add an option to omit results from the preamble.

Summary:
Enumerating the contents of a namespace or global scope will omit any
decls that aren't already loaded, instead of deserializing them from the
PCH.

This allows a fast hybrid code completion where symbols from headers are
provided by an external index. (Sema already exposes the information
needed to do a reasonabl job of filtering them).
Clangd plans to implement this hybrid.

This option is just a hint - callers still need to postfilter results if
they want to *avoid* completing decls outside the main file.

Reviewers: bkramer, ilya-biryukov

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D41989

llvm-svn: 322371

1 files changed, 8 insertions, 1 deletions

diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
index a0c4dc98ada..775b7acc946 100644
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -5161,7 +5161,14 @@ enum CXCodeComplete_Flags {
    * \brief Whether to include brief documentation within the set of code
    * completions returned.
    */
-  CXCodeComplete_IncludeBriefComments = 0x04
+  CXCodeComplete_IncludeBriefComments = 0x04,
+
+  /**
+   * \brief Whether to speed up completion by omitting some entities which are
+   * defined in the preamble. There's no guarantee any particular entity will
+   * be omitted. This may be useful if the headers are indexed externally.
+   */
+  CXCodeComplete_SkipPreamble = 0x08
 };
 
 /**