[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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@322371 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 24 insertions, 4 deletions

diff --git a/include/clang-c/Index.h b/include/clang-c/Index.h
index a0c4dc98ad..775b7acc94 100644
--- a/include/clang-c/Index.h
+++ b/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
 };
 
 /**
diff --git a/include/clang/Sema/CodeCompleteConsumer.h b/include/clang/Sema/CodeCompleteConsumer.h
index 5d280b5608..e8db3ec237 100644
--- a/include/clang/Sema/CodeCompleteConsumer.h
+++ b/include/clang/Sema/CodeCompleteConsumer.h
@@ -934,6 +934,12 @@ public:
     return CodeCompleteOpts.IncludeBriefComments;
   }
 
+  /// \brief Hint whether to load data from the external AST in order to provide
+  /// full results. If false, declarations from the preamble may be omitted.
+  bool loadExternal() const {
+    return CodeCompleteOpts.LoadExternal;
+  }
+
   /// \brief Determine whether the output of this consumer is binary.
   bool isOutputBinary() const { return OutputIsBinary; }
 
diff --git a/include/clang/Sema/CodeCompleteOptions.h b/include/clang/Sema/CodeCompleteOptions.h
index 091d8ca605..bfba2be3ec 100644
--- a/include/clang/Sema/CodeCompleteOptions.h
+++ b/include/clang/Sema/CodeCompleteOptions.h
@@ -35,9 +35,14 @@ public:
   /// Show brief documentation comments in code completion results.
   unsigned IncludeBriefComments : 1;
 
+  /// Hint whether to load data from the external AST in order to provide
+  /// full results. If false, declarations from the preamble may be omitted.
+  unsigned LoadExternal : 1;
+
   CodeCompleteOptions()
       : IncludeMacros(0), IncludeCodePatterns(0), IncludeGlobals(1),
-        IncludeNamespaceLevelDecls(1), IncludeBriefComments(0) {}
+        IncludeNamespaceLevelDecls(1), IncludeBriefComments(0),
+        LoadExternal(1) {}
 };
 
 } // namespace clang
diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index b4afd073c6..23aa3565d1 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -3199,11 +3199,13 @@ public:
 
   void LookupVisibleDecls(Scope *S, LookupNameKind Kind,
                           VisibleDeclConsumer &Consumer,
-                          bool IncludeGlobalScope = true);
+                          bool IncludeGlobalScope = true,
+                          bool LoadExternal = true);
   void LookupVisibleDecls(DeclContext *Ctx, LookupNameKind Kind,
                           VisibleDeclConsumer &Consumer,
                           bool IncludeGlobalScope = true,
-                          bool IncludeDependentBases = false);
+                          bool IncludeDependentBases = false,
+                          bool LoadExternal = true);
 
   enum CorrectTypoKind {
     CTK_NonError,     // CorrectTypo used in a non error recovery situation.