[Macros] Fix visiting nested conformance macro declarations in SIL and IRGen.

When expanding a conformance macro, the generated extension decls are added to
the TopLevelDecls vector of the synthesized file unit to expose them to
sf->getSynthesizedFile()->getTopLevelDecls(). There are two problems with this:

  1. These decls are also visited via visitAuxiliaryDecls() for the purpose of
     type checking. This causes problems in code generation because the extensions
     are visited separately, and because SIL and IRGen assume nested auxiliary decls
     are members.
  2. SILGen only emits top-level decls directly from the source file rather than its
     synthesized file. Auxiliary decls are visited here, but this doesn't work for
     nested conformance macros because the attached-to decl is not at the top-level,
     so macro-generated conformances for nested types never emit their descriptor.

To fix this in the short term, visit top-level decls in the synthesized file that are
generated by conformance macros, and skip auxiliary extension decls when emitting type
members. This fix is narrowly scoped to only impact macros, but in the future this
warrants a more structural fix to better handle top-level decls in the synthesized file.

Author: hborla

lib/IRGen/GenDecl.cpp

@@ -5501,6 +5501,11 @@ void IRGenModule::emitNestedTypeDecls(DeclRange members) {
       continue;
 
     member->visitAuxiliaryDecls([&](Decl *decl) {
+      // FIXME: Conformance macros can generate extension decls. These
+      // are visited as top-level decls; skip them here.
+      if (isa<ExtensionDecl>(decl))
+        return;
+
       emitNestedTypeDecls({decl, nullptr});
     });
     switch (member->getKind()) {

lib/SILGen/SILGen.cpp

@@ -2196,6 +2196,10 @@ class SILGenModuleRAII {
     for (auto *D : sf->getTopLevelDecls()) {
       // Emit auxiliary decls.
       D->visitAuxiliaryDecls([&](Decl *auxiliaryDecl) {
+        // Skip extensions decls; they are visited below.
+        if (isa<ExtensionDecl>(auxiliaryDecl))
+          return;
+
         FrontendStatsTracer StatsTracer(SGM.getASTContext().Stats,
                                         "SILgen-decl", auxiliaryDecl);
         SGM.visit(auxiliaryDecl);
@@ -2206,6 +2210,34 @@ class SILGenModuleRAII {
       SGM.visit(D);
     }
 
+    // FIXME: Visit macro-generated extensions separately.
+    //
+    // The code below that visits auxiliary decls of the top-level
+    // decls in the source file does not work for nested types with
+    // attached conformance macros:
+    // ```
+    // struct Outer {
+    //   @AddConformance struct Inner {}
+    // }
+    // ```
+    // Because the attached-to decl is not at the top-level. To fix this,
+    // visit the macro-generated conformances that are recorded in the
+    // synthesized file unit to cover all macro-generated extension decls.
+    if (auto *synthesizedFile = sf->getSynthesizedFile()) {
+      for (auto *D : synthesizedFile->getTopLevelDecls()) {
+        if (!isa<ExtensionDecl>(D))
+          continue;
+
+        auto *sf = D->getInnermostDeclContext()->getParentSourceFile();
+        if (sf->getFulfilledMacroRole() != MacroRole::Conformance)
+          continue;
+
+        FrontendStatsTracer StatsTracer(SGM.getASTContext().Stats,
+                                        "SILgen-decl", D);
+        SGM.visit(D);
+      }
+    }
+
     for (Decl *D : sf->getHoistedDecls()) {
       FrontendStatsTracer StatsTracer(SGM.getASTContext().Stats,
                                       "SILgen-decl", D);

lib/SILGen/SILGenType.cpp

@@ -1086,6 +1086,11 @@ class SILGenType : public TypeMemberVisitor<SILGenType> {
     SGM.emitLazyConformancesForType(theType);
 
     forEachMemberToLower(theType, [&](Decl *member) {
+      // FIXME: Conformance macros can generate extension decls. These
+      // are visited as top-level decls; skip them here.
+      if (isa<ExtensionDecl>(member))
+        return;
+
       visit(member);
     });
 

test/Macros/macro_expand_conformances.swift

@@ -29,6 +29,10 @@ struct S {}
 @Hashable
 struct S2 {}
 
+enum E {
+  @Equatable struct Nested {}
+}
+
 // CHECK-DUMP: @__swiftmacro_25macro_expand_conformances1S9EquatablefMc_.swift
 // CHECK-DUMP: extension S : Equatable  {}
 
@@ -38,6 +42,8 @@ requireEquatable(S())
 requireEquatable(S2())
 requireHashable(S2())
 
+requireEquatable(E.Nested())
+
 @attached(conformance)
 @attached(member, names: named(requirement))
 macro DelegatedConformance() = #externalMacro(module: "MacroDefinition", type: "DelegatedConformanceMacro")