[CodeCompletion] Provide argument label completions inside #externalMacro

rdar://108163809
rdar://108681394

Author: ahoppen

lib/Sema/TypeCheckMacros.cpp

@@ -193,6 +193,13 @@ MacroDefinition MacroDefinitionRequest::evaluate(
     free(replacements);
   };
 
+  if (checkResult < 0 && ctx.CompletionCallback) {
+    // If the macro failed to check and we are in code completion mode, pretend
+    // it's an arbitrary macro. This allows us to get call argument completions
+    // inside `#externalMacro`.
+    checkResult = BridgedMacroDefinitionKind::BridgedExpandedMacro;
+  }
+
   if (checkResult < 0)
     return MacroDefinition::forInvalid();
 

test/IDE/complete_macro_declaration.swift

@@ -3,5 +3,19 @@
 
 let globalVar = 1
 macro expect(file: Int = #^DEFAULT_ARG^#) = #externalMacro(module: "MyModule", type: "MyMacro")
-
 // DEFAULT_ARG: Decl[GlobalVar]/CurrModule/TypeRelation[Convertible]: globalVar[#Int#]; name=globalVar
+
+@freestanding(expression)
+macro externalMacro() = ##^EXTERNAL_MACRO^#externalMacro
+// EXTERNAL_MACRO: Decl[Macro]/OtherModule[Swift]/IsSystem: externalMacro({#module: String#}, {#type: String#})[#T#]; name=externalMacro(module:type:)
+
+@freestanding(expression)
+macro externalMacroWithTrailing() = ##^EXTERNAL_MACRO_WITH_TRAILING?check=EXTERNAL_MACRO^#externalMacro
+
+@freestanding(expression)
+macro externalMacroCallPattern() = #externalMacro(#^EXTERNAL_MACRO_CALL_PATTERN^#)
+// EXTERNAL_MACRO_CALL_PATTERN: Pattern/None/Flair[ArgLabels]/TypeRelation[Convertible]: ['(']{#module: String#}, {#type: String#}[')'][#Void#]; name=module:type:
+
+@freestanding(expression)
+macro externalMacroCallPattern() = #externalMacro(module: "MyModule", #^EXTERNAL_MACRO_TYPE_ARG_LABEL^#)
+// EXTERNAL_MACRO_TYPE_ARG_LABEL: Pattern/Local/Flair[ArgLabels]:     {#type: String#}[#String#]; name=type: