[Macros] Add debug logs for macro expansions

These can be enabled with `-Xcc -mllvm -debug-only=macros`.

Author: hnrklssn

lib/Sema/TypeCheckMacros.cpp

@@ -52,6 +52,8 @@
 #include "swift/Subsystems.h"
 #include "llvm/Config/config.h"
 
+#define DEBUG_TYPE "macros"
+
 using namespace swift;
 
 /// Translate an argument provided as a string literal into an identifier,
@@ -1201,6 +1203,11 @@ evaluateFreestandingMacro(FreestandingMacroExpansion *expansion,
 
     PrettyStackTraceFreestandingMacroExpansion debugStack(
         "expanding freestanding macro", expansion);
+    LLVM_DEBUG(
+      llvm::dbgs() << "\nexpanding macro:\n";
+      macro->print(llvm::dbgs(), PrintOptions::printEverything());
+      llvm::dbgs() << "\n";
+    );
 
     // Builtin macros are handled via ASTGen.
     auto *astGenSourceFile = sourceFile->getExportedSourceFile();
@@ -1527,6 +1534,18 @@ static SourceFile *evaluateAttachedMacro(MacroDecl *macro, Decl *attachedTo,
     auto *astGenAttrSourceFile = attrSourceFile->getExportedSourceFile();
     if (!astGenAttrSourceFile)
       return nullptr;
+    LLVM_DEBUG(
+      StreamPrinter P(llvm::dbgs());
+      llvm::dbgs() << "\nexpanding macro:\n";
+      attr->print(P, PrintOptions::printEverything(), attachedTo);
+      llvm::dbgs() << "\nattached to:\n";
+      attachedTo->print(P, PrintOptions::printEverything());
+      if (parentDecl) {
+        llvm::dbgs() << "\nwith parent:\n";
+        parentDecl->print(P, PrintOptions::printEverything());
+      }
+      llvm::dbgs() << "\n";
+    );
 
     auto *astGenDeclSourceFile = declSourceFile->getExportedSourceFile();
     if (!astGenDeclSourceFile)
@@ -1677,6 +1696,14 @@ static SourceFile *evaluateAttachedMacro(MacroDecl *macro,
 #if SWIFT_BUILD_SWIFT_SYNTAX
     PrettyStackTraceExpr debugStack(
       ctx, "expanding attached macro", attachedTo);
+    LLVM_DEBUG(
+      StreamPrinter P(llvm::dbgs());
+      llvm::dbgs() << "\nexpanding macro:\n";
+      attr->print(P, PrintOptions::printEverything(), nullptr);
+      llvm::dbgs() << "\nattached to:\n";
+      attachedTo->print(P, PrintOptions::printEverything());
+      llvm::dbgs() << "\n";
+    );
 
     auto *astGenAttrSourceFile = attrSourceFile->getExportedSourceFile();
     if (!astGenAttrSourceFile)