SE-0022: Code completion for #selector.

Author: DougGregor

lib/IDE/CodeCompletion.cpp

@@ -1985,6 +1985,21 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
     Builder.addRightParen();
   }
 
+  void addPoundSelector() {
+    // #selector is only available when the Objective-C runtime is.
+    if (!Ctx.LangOpts.EnableObjCInterop) return;
+
+    CodeCompletionResultBuilder Builder(
+                                  Sink,
+                                  CodeCompletionResult::ResultKind::Keyword,
+                                  SemanticContextKind::ExpressionSpecific,
+                                  ExpectedTypes);
+    Builder.addTextChunk("selector");
+    Builder.addLeftParen();
+    Builder.addSimpleTypedParameter("@objc method", /*isVarArg=*/false);
+    Builder.addRightParen();
+  }
+
   void addFunctionCallPattern(const AnyFunctionType *AFT,
                               const AbstractFunctionDecl *AFD = nullptr) {
     foundFunction(AFT);
@@ -4569,6 +4584,7 @@ void CodeCompletionCallbacksImpl::doneParsing() {
 
   case CompletionKind::AfterPound: {
     Lookup.addPoundAvailable(ParentStmtKind);
+    Lookup.addPoundSelector();
     break;
   }
   }

test/IDE/complete_pound_selector.swift

@@ -0,0 +1,10 @@
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=AFTER_POUND | FileCheck %s
+
+// REQUIRES: objc_interop
+
+{
+  if ##^AFTER_POUND^#
+}
+
+// CHECK: Keyword/ExprSpecific:               available({#Platform...#}, *); name=available(Platform..., *)
+// CHECK: Keyword/ExprSpecific:               selector({#@objc method#}); name=selector(@objc method)