[Macros] Teach SILGen to visit declartions produced by freestanding macros

Fixes a crash where local variables introduced by a freestanding
declaration macro would not get SIL emitted for them, rdar://109721114.

Author: DougGregor

include/swift/AST/Decl.h

@@ -8605,8 +8605,9 @@ class MacroExpansionDecl : public Decl, public FreestandingMacroExpansion {
     return getExpansionInfo()->getSourceRange();
   }
   SourceLoc getLocFromSource() const { return getExpansionInfo()->SigilLoc; }
-  using ExprOrStmtExpansionCallback = llvm::function_ref<void(ASTNode)>;
-  void forEachExpandedExprOrStmt(ExprOrStmtExpansionCallback) const;
+
+  /// Enumerate the nodes produced by expanding this macro expansion.
+  void forEachExpandedNode(llvm::function_ref<void(ASTNode)> callback) const;
 
   /// Returns a discriminator which determines this macro expansion's index
   /// in the sequence of macro expansions within the current function.

lib/AST/ASTWalker.cpp

@@ -458,19 +458,18 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
     // Visit auxiliary decls, which may be decls from macro expansions.
     bool alreadyFailed = false;
     if (shouldWalkExpansion) {
-      MED->visitAuxiliaryDecls([&](Decl *decl) {
-        if (alreadyFailed) return;
-        if (!isa<VarDecl>(decl))
-          alreadyFailed = inherited::visit(decl);
-      });
-      MED->forEachExpandedExprOrStmt([&](ASTNode expandedNode) {
+      MED->forEachExpandedNode([&](ASTNode expandedNode) {
         if (alreadyFailed) return;
         if (auto *expr = expandedNode.dyn_cast<Expr *>()) {
           if (!doIt(expr))
             alreadyFailed = true;
         } else if (auto *stmt = expandedNode.dyn_cast<Stmt *>()) {
           if (!doIt(stmt))
             alreadyFailed = true;
+        } else {
+          auto decl = expandedNode.get<Decl *>();
+          if (!isa<VarDecl>(decl))
+            alreadyFailed = inherited::visit(decl);
         }
       });
     }

lib/AST/Decl.cpp

@@ -10637,8 +10637,9 @@ unsigned MacroExpansionDecl::getDiscriminator() const {
   return getRawDiscriminator();
 }
 
-void MacroExpansionDecl::forEachExpandedExprOrStmt(
-    ExprOrStmtExpansionCallback callback) const {
+void MacroExpansionDecl::forEachExpandedNode(
+    llvm::function_ref<void(ASTNode)> callback
+) const {
   auto mutableThis = const_cast<MacroExpansionDecl *>(this);
   auto bufferID = evaluateOrDefault(
       getASTContext().evaluator,
@@ -10650,8 +10651,7 @@ void MacroExpansionDecl::forEachExpandedExprOrStmt(
   auto startLoc = sourceMgr.getLocForBufferStart(*bufferID);
   auto *sourceFile = moduleDecl->getSourceFileContainingLocation(startLoc);
   for (auto node : sourceFile->getTopLevelItems())
-    if (node.is<Expr *>() || node.is<Stmt *>())
-      callback(node);
+    callback(node);
 }
 
 NominalTypeDecl *

lib/SILGen/SILGenDecl.cpp

@@ -1606,11 +1606,13 @@ void SILGenFunction::visitVarDecl(VarDecl *D) {
 }
 
 void SILGenFunction::visitMacroExpansionDecl(MacroExpansionDecl *D) {
-  D->forEachExpandedExprOrStmt([&](ASTNode node) {
+  D->forEachExpandedNode([&](ASTNode node) {
     if (auto *expr = node.dyn_cast<Expr *>())
       emitIgnoredExpr(expr);
     else if (auto *stmt = node.dyn_cast<Stmt *>())
       emitStmt(stmt);
+    else
+      visit(node.get<Decl *>());
   });
 }
 

lib/SILGen/SILGenExpr.cpp

@@ -6246,11 +6246,13 @@ RValue RValueEmitter::visitMacroExpansionExpr(MacroExpansionExpr *E,
   }
   else if (auto *MED = E->getSubstituteDecl()) {
     Mangle::ASTMangler mangler;
-    MED->forEachExpandedExprOrStmt([&](ASTNode node) {
+    MED->forEachExpandedNode([&](ASTNode node) {
       if (auto *expr = node.dyn_cast<Expr *>())
         visit(expr, C);
       else if (auto *stmt = node.dyn_cast<Stmt *>())
         SGF.emitStmt(stmt);
+      else
+        SGF.visit(node.get<Decl *>());
     });
     return RValue();
   }

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2061,8 +2061,11 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
   void visitMacroExpansionDecl(MacroExpansionDecl *MED) {
     // Assign a discriminator.
     (void)MED->getDiscriminator();
-    // Decls in expansion already visited as auxiliary decls.
-    MED->forEachExpandedExprOrStmt([&](ASTNode node) {
+    MED->forEachExpandedNode([&](ASTNode node) {
+      // Decls in expansion already visited as auxiliary decls.
+      if (node.is<Decl *>())
+        return;
+
       TypeChecker::typeCheckASTNode(node, MED->getDeclContext());
     });
   }

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -299,6 +299,24 @@ public struct DefineDeclsWithKnownNamesMacro: DeclarationMacro {
   }
 }
 
+public struct VarDeclMacro: DeclarationMacro {
+  public static func expansion(
+    of node: some FreestandingMacroExpansionSyntax,
+    in context: some MacroExpansionContext
+  ) throws -> [DeclSyntax] {
+    return [
+      """
+      let fromMacro = 23
+      use(fromMacro)
+      if true {
+        let fromMacro = "string"
+        use(fromMacro)
+      }
+      """
+    ]
+  }
+}
+
 public struct WarningMacro: ExpressionMacro {
    public static func expansion(
      of macro: some FreestandingMacroExpansionSyntax,

test/Macros/macro_expand.swift

@@ -151,6 +151,13 @@ func testFileID(a: Int, b: Int) {
 
 testFileID(a: 1, b: 2)
 
+@freestanding(declaration, names: named(fromMacro)) macro varDecl() = #externalMacro(module: "MacroDefinition", type: "VarDeclMacro")
+
+func testVarDecl() {
+  func use<T>(_ t: T) {}
+  #varDecl()
+}
+
 @freestanding(expression) macro stringifyAndTry<T>(_ value: T) -> (T, String) =
     #externalMacro(module: "MacroDefinition", type: "StringifyAndTryMacro")