[Macros] Add tests for redeclarations of macros

Author: DougGregor

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -1984,7 +1984,6 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
 
   void visitMacroDecl(MacroDecl *MD) {
     TypeChecker::checkDeclAttributes(MD);
-    // FIXME: Check for redeclarations
     checkAccessControl(MD);
   }
 

test/Macros/macros_diagnostics.swift

@@ -13,6 +13,18 @@ internal struct X { } // expected-note{{type declared here}}
 public macro createAnX: X = BuiltinMacros.Blah
 // expected-error@-1{{macro cannot be declared public because its result type uses an internal type}}
 
+macro m1: Int = A.B
+macro m1: Float = A.B
+
+macro m2: Int = A.B // expected-note{{'m2' previously declared here}}
+macro m2: Int = A.B // expected-error{{invalid redeclaration of 'm2'}}
+
+macro m3(_: Int) -> Int = A.B
+macro m3(_: Int) -> Float = A.B
+
+macro m4(_: Int) -> Int = A.B // expected-note{{'m4' previously declared here}}
+macro m4(_: Int) -> Int = A.B // expected-error{{invalid redeclaration of 'm4'}}
+
 func test(a: Int, b: Int) {
   // FIXME: Bad diagnostic.
   let s = #stringify<Int, Int>(a + b) // expected-error{{type of expression is ambiguous without more context}}