[Macros] Pass evaluated macro source back into the C++ part of the compiler.

Use this to print out the rewritten macro, for now.

Author: DougGregor

lib/ASTGen/Sources/ASTGen/Macros.swift

@@ -20,11 +20,17 @@ extension SyntaxProtocol {
   }
 }
 
-@_cdecl("swift_ASTGen_printMacroResult")
-public func printMacroResult(
-  sourceFilePtr: UnsafeRawPointer,
-  sourceLocationPtr: UnsafePointer<UInt8>?
+@_cdecl("swift_ASTGen_evaluateMacro")
+public func evaluateMacro(
+  sourceFilePtr: UnsafePointer<UInt8>,
+  sourceLocationPtr: UnsafePointer<UInt8>?,
+  expandedSourcePointer: UnsafeMutablePointer<UnsafePointer<UInt8>?>,
+  expandedSourceLength: UnsafeMutablePointer<Int>
 ) -> Int {
+  // We didn't expand anything so far.
+  expandedSourcePointer.pointee = nil
+  expandedSourceLength.pointee = 0
+
   guard let sourceLocationPtr = sourceLocationPtr else {
     print("NULL source location")
     return -1
@@ -68,7 +74,17 @@ public func printMacroResult(
       /* TODO: Report errors */
     }
 
-    print("Macro rewrite: \(parentSyntax.withoutTrivia()) --> \(evaluatedSyntax.withoutTrivia())")
+    var evaluatedSyntaxStr = evaluatedSyntax.withoutTrivia().description
+    evaluatedSyntaxStr.withUTF8 { utf8 in
+      let evaluatedResultPtr = UnsafeMutablePointer<UInt8>.allocate(capacity: utf8.count + 1)
+      if let baseAddress = utf8.baseAddress {
+        evaluatedResultPtr.initialize(from: baseAddress, count: utf8.count)
+      }
+      evaluatedResultPtr[utf8.count] = 0
+
+      expandedSourcePointer.pointee = UnsafePointer(evaluatedResultPtr)
+      expandedSourceLength.pointee = utf8.count + 1
+    }
 
     return 0
   }

lib/Sema/CSApply.cpp

@@ -54,8 +54,9 @@
 using namespace swift;
 using namespace constraints;
 
-extern "C" ptrdiff_t swift_ASTGen_printMacroResult(
-    void *sourceFile, const void *sourceLocation);
+extern "C" ptrdiff_t swift_ASTGen_evaluateMacro(
+    void *sourceFile, const void *sourceLocation,
+    const char **evaluatedSource, ptrdiff_t *evaluatedSourceLength);
 
 bool Solution::hasFixedType(TypeVariableType *typeVar) const {
   auto knownBinding = typeBindings.find(typeVar);
@@ -2978,8 +2979,18 @@ namespace {
       if (ctx.LangOpts.hasFeature(Feature::BuiltinMacros)) {
         if (auto sf = dc->getParentSourceFile()) {
           if (auto astGenSF = sf->exportedSourceFile) {
-            swift_ASTGen_printMacroResult(
-                astGenSF, expr->getStartLoc().getOpaquePointerValue());
+            const char *evaluatedSource;
+            ptrdiff_t evaluatedSourceLength;
+            swift_ASTGen_evaluateMacro(
+                astGenSF, expr->getStartLoc().getOpaquePointerValue(),
+                &evaluatedSource, &evaluatedSourceLength);
+            if (evaluatedSource) {
+              llvm::outs() << "Macro rewrite: "
+                << MagicIdentifierLiteralExpr::getKindString(expr->getKind())
+                << " --> " << StringRef(evaluatedSource, evaluatedSourceLength)
+                << "\n";
+              free((void*)evaluatedSource);
+            }
           }
         }
       }