[Sema] TypeCheckProtocolInference: using trailingWhereClause to get self bounds in source file.

Author: hank121314

lib/AST/NameLookup.cpp

@@ -983,9 +983,6 @@ SelfBounds swift::getSelfBoundsFromWhereClause(
 SelfBounds SelfBoundsFromGenericSignatureRequest::evaluate(
     Evaluator &evaluator, const ExtensionDecl *extDecl) const {
   SelfBounds result;
-  if (!extDecl->hasComputedGenericSignature())
-    return result;
-
   ASTContext &ctx = extDecl->getASTContext();
   auto selfType = extDecl->getSelfInterfaceType();
   for (const auto &req : extDecl->getGenericRequirements()) {

lib/Sema/TypeCheckProtocolInference.cpp

@@ -220,8 +220,16 @@ AssociatedTypeInference::inferTypeWitnessesViaValueWitnesses(
     if (!checkConformance(proto))
       return false;
 
-    // Now check any additional bounds on 'Self' from the generic signature.
-    auto bounds = getSelfBoundsFromGenericSignature(extension);
+    // Source file and module file have different ways to get self bounds.
+    // Source file extension will have trailing where clause which can avoid
+    // computing a generic signature. Module file will not have
+    // trailing where clause, so it will compute generic signature to get
+    // self bounds which might result in slow performance.
+    SelfBounds bounds;
+    if (extension->getParentSourceFile() != nullptr)
+      bounds = getSelfBoundsFromWhereClause(extension);
+    else
+      bounds = getSelfBoundsFromGenericSignature(extension);
     for (auto *decl : bounds.decls) {
       if (auto *proto = dyn_cast<ProtocolDecl>(decl)) {
         if (!checkConformance(proto))

test/Sema/Inputs/sr15807_a.swift renamed to test/Sema/Inputs/where_clause_across_module_boundaries_module.swift

@@ -0,0 +1,17 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -o %t/ModuleA.swiftmodule %S/Inputs/where_clause_across_module_boundaries_module.swift
+// RUN: %target-swift-frontend -I %t -emit-sil -verify %s
+
+// SR-15807:
+// Associated Type Inference fails across module boundaries
+// Self bounds from where clause cannot be accessed across modules.
+// This test is intended to test whether it can use generic signature to get self bounds.
+import Foundation
+import ModuleA
+
+struct ModuleBFoo: Codable, DefaultsSerializable {
+}
+
+enum ModuleBBar: Int, Codable, DefaultsSerializable { // expected-error {{type 'ModuleBBar' does not conform to protocol 'DefaultsSerializable'}}
+  case foo, bar
+}