[Macros] Don't visit macro-generated extensions in 'visitAuxiliaryDecls'.

Macro-generated extensions are hoisted to file scope, because extensions are
not valid in nested scopes. Callers of 'visitAuxiliaryDecls' assume that the
auxiliary decls are in the same decl context as the original, which is clearly
not the case for extensions, and it leads to issues like visiting extension at
the wrong time during SILGen. The extensions are already added to the top-level
decls, so we don't need to visit them as auxiliary decls as long as we type check
them eagerly after expansion.

Author: hborla

lib/AST/Decl.cpp

@@ -407,20 +407,6 @@ void Decl::visitAuxiliaryDecls(
     }
   }
 
-  if (auto *nominal = dyn_cast<NominalTypeDecl>(mutableThis)) {
-    auto conformanceBuffers =
-        evaluateOrDefault(ctx.evaluator,
-                          ExpandConformanceMacros{nominal},
-                          {});
-    for (auto bufferID : conformanceBuffers) {
-      auto startLoc = sourceMgr.getLocForBufferStart(bufferID);
-      auto *sourceFile = moduleDecl->getSourceFileContainingLocation(startLoc);
-      for (auto *extension : sourceFile->getTopLevelDecls()) {
-        callback(extension);
-      }
-    }
-  }
-
   if (visitFreestandingExpanded) {
     if (auto *med = dyn_cast<MacroExpansionDecl>(mutableThis)) {
       if (auto bufferID = evaluateOrDefault(

lib/SILGen/SILGenType.cpp

@@ -1101,11 +1101,6 @@ 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);
     });
 

lib/Sema/TypeCheckMacros.cpp

@@ -1446,6 +1446,16 @@ swift::expandConformances(CustomAttr *attr, MacroDecl *macro,
     if (auto file = dyn_cast<FileUnit>(
             decl->getDeclContext()->getModuleScopeContext()))
       file->getOrCreateSynthesizedFile().addTopLevelDecl(extension);
+
+    // Most other macro-generated declarations are visited and type-checked
+    // through calling 'visitAuxiliaryDecls' on the original declaration the
+    // macro is attached to. We don't do this for macro-generated extensions,
+    // because the extension is not a peer of the original declaration. Instead
+    // of requiring all callers of 'visitAuxiliarDecls' to understsand the
+    // hoisting behavior of macro-generated extensions, we simply expose the
+    // extension to 'getTopLevelDecls()' and type check the extension eagerly
+    // here.
+    TypeChecker::typeCheckDecl(extension);
   }
 
   return macroSourceFile->getBufferID();

test/Macros/macro_expand_conformances.swift

@@ -63,6 +63,12 @@ requireHashable(S2())
 
 requireEquatable(E.Nested())
 
+extension E {
+  @Equatable struct NestedInExtension {}
+}
+
+requireEquatable(E.NestedInExtension())
+
 #if TEST_DIAGNOSTICS
 requireEquatable(PublicEquatable())