Make the interface type of a generic macro into a GenericFunctionType.

This correctly models their type in the type system, and fixes the
redeclaration issue reported in rdar://104183961.

Author: DougGregor

lib/IDE/CompletionLookup.cpp

@@ -1808,7 +1808,7 @@ void CompletionLookup::addMacroExpansion(const MacroDecl *MD,
   Type macroType = MD->getInterfaceType();
   if (MD->parameterList && MD->parameterList->size() > 0) {
     Builder.addLeftParen();
-    addCallArgumentPatterns(Builder, macroType->castTo<FunctionType>(),
+    addCallArgumentPatterns(Builder, macroType->castTo<AnyFunctionType>(),
                             MD->parameterList,
                             MD->getGenericSignature());
     Builder.addRightParen();

lib/Sema/ConstraintSystem.cpp

@@ -1673,14 +1673,13 @@ ConstraintSystem::getTypeOfReference(ValueDecl *value,
 
     // Open any the generic types.
     OpenedTypeMap replacements;
-    openGeneric(macro->getParentModule(), macro->getGenericSignature(),
-                locator, replacements);
+    Type openedType = openFunctionType(
+        macroType->castTo<AnyFunctionType>(), locator, replacements,
+        macro->getDeclContext());
 
     // If we opened up any type variables, record the replacements.
     recordOpenedTypes(locator, replacements);
 
-    Type openedType = openType(macroType, replacements);
-
     // FIXME: Should we use replaceParamErrorTypeByPlaceholder() here?
 
     return { openedType, openedType, openedType, openedType };

lib/Sema/TypeCheckDecl.cpp

@@ -2595,8 +2595,15 @@ InterfaceTypeRequest::evaluate(Evaluator &eval, ValueDecl *D) const {
 
     SmallVector<AnyFunctionType::Param, 4> paramTypes;
     macro->parameterList->getParams(paramTypes);
-    FunctionType::ExtInfo info;
-    return FunctionType::get(paramTypes, resultType, info);
+
+    if (auto genericSig = macro->getGenericSignature()) {
+      GenericFunctionType::ExtInfo info;
+      return GenericFunctionType::get(
+          genericSig, paramTypes, resultType, info);
+    } else {
+      FunctionType::ExtInfo info;
+      return FunctionType::get(paramTypes, resultType, info);
+    }
   }
   }
   llvm_unreachable("invalid decl kind");

test/Macros/macros_diagnostics.swift

@@ -63,6 +63,15 @@ func overloaded1(_ p: Any) { }
 @freestanding(expression) macro notOverloaded1(_ p: P) = #externalMacro(module: "MissingModule", type: "MissingOtherType") // expected-error{{invalid redeclaration of 'notOverloaded1'}}
 // expected-warning@-1{{external macro implementation type}}
 
+// Overloading based on generic constraint.
+public protocol ResultBuilder {
+}
+
+@freestanding(expression) public macro ApplyBuilder<R: ResultBuilder>(resultBuilder: R.Type, to closure: () -> Void) -> (() -> String) = #externalMacro(module: "MacroExamplesPlugin", type: "ResultBuilderMacro")
+// expected-warning@-1{{external macro implementation type}}
+@freestanding(expression)  public macro ApplyBuilder<R>(resultBuilder: R.Type, to closure: () -> Void) -> (() -> String) = #externalMacro(module: "MacroExamplesPlugin", type: "ResultBuilderMacro2")
+// expected-warning@-1{{external macro implementation type}}
+
 @freestanding(expression) macro intIdentity(value: Int, _: Float) -> Int = #externalMacro(module: "MissingModule", type: "MissingType")
 // expected-note@-1{{'intIdentity(value:_:)' declared here}}
 // expected-warning@-2{{external macro implementation type}}