SE-0106: Add "macOS" as an alias of "OSX" for #if.

...by canonicalizing it to the known platform name. This isn't a
wonderful answer, but it preserves the invariant that a platform
condition has at most one value.

A later commit will switch which one is the default.

Author: jrose-apple

include/swift/Basic/LangOptions.h

@@ -235,7 +235,10 @@ namespace swift {
 
     /// Returns true if the 'os' platform condition argument represents
     /// a supported target operating system.
-    static bool isPlatformConditionOSSupported(StringRef OSName);
+    ///
+    /// Note that this also canonicalizes the OS name if the check returns
+    /// true.
+    static bool checkPlatformConditionOS(StringRef &OSName);
 
     /// Returns true if the 'arch' platform condition argument represents
     /// a supported target architecture.

lib/Basic/LangOptions.cpp

@@ -55,7 +55,9 @@ bool contains(const Type (&Array)[N], const Type &V) {
   return std::find(std::begin(Array), std::end(Array), V) != std::end(Array);
 }
 
-bool LangOptions::isPlatformConditionOSSupported(StringRef OSName) {
+bool LangOptions::checkPlatformConditionOS(StringRef &OSName) {
+  if (OSName == "macOS")
+    OSName = "OSX";
   return contains(SupportedConditionalCompilationOSs, OSName);
 }
 

lib/Parse/ParseStmt.cpp

@@ -1711,7 +1711,7 @@ Parser::evaluateConditionalCompilationExpr(Expr *condition) {
           return ConditionalCompilationExprState::error();
         }
         if (fnName == "os") {
-          if (!LangOptions::isPlatformConditionOSSupported(argument)) {
+          if (!LangOptions::checkPlatformConditionOS(argument)) {
             diagnose(UDRE->getLoc(), diag::unknown_platform_condition_argument,
                      "operating system", fnName);
             return ConditionalCompilationExprState::error();

test/Parse/ConditionalCompilation/x64OSXTarget.swift

@@ -6,3 +6,10 @@ class C {}
 var x = C()
 #endif
 var y = x
+
+
+#if arch(x86_64) && os(macOS) && _runtime(_ObjC) && _endian(little)
+class CC {}
+var xx = CC()
+#endif
+var yy = xx