[Frontend] Avoid running plugins during code completion parse

The parsing that is done for code completion is a special case that will
discard any generated diagnostics, so avoid running plugins for this
case in the first place to avoid performance penalties due to the
plugins.

A scenario for this is for example libclang with extra plugins like tidy.

Patch by Nikolai Kosjar

Differential Revision: https://reviews.llvm.org/D46050

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@332469 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Frontend/FrontendAction.cpp

@@ -150,12 +150,16 @@ FrontendAction::CreateWrappedASTConsumer(CompilerInstance &CI,
     return nullptr;
 
   // If there are no registered plugins we don't need to wrap the consumer
-  if (FrontendPluginRegistry::begin() == FrontendPluginRegistry::end())
-    return Consumer;
-
-  // Collect the list of plugins that go before the main action (in Consumers)
-  // or after it (in AfterConsumers)
-  std::vector<std::unique_ptr<ASTConsumer>> Consumers;
+  if (FrontendPluginRegistry::begin() == FrontendPluginRegistry::end())
+    return Consumer;
+
+  // If this is a code completion run, avoid invoking the plugin consumers
+  if (CI.hasCodeCompletionConsumer())
+    return Consumer;
+
+  // Collect the list of plugins that go before the main action (in Consumers)
+  // or after it (in AfterConsumers)
+  std::vector<std::unique_ptr<ASTConsumer>> Consumers;
   std::vector<std::unique_ptr<ASTConsumer>> AfterConsumers;
   for (FrontendPluginRegistry::iterator it = FrontendPluginRegistry::begin(),
                                         ie = FrontendPluginRegistry::end();

test/Index/complete-and-plugins.c

@@ -0,0 +1,6 @@
+// RUN: c-index-test -code-completion-at=%s:7:1 -load %llvmshlibdir/PrintFunctionNames%pluginext -add-plugin print-fns %s | FileCheck %s
+// REQUIRES: plugins, examples
+// CHECK: macro definition:{{.*}}
+// CHECK-NOT: top-level-decl: "x"
+
+void x();