From fda2ddb86a087c6b711957d8646bb6a2dad42922 Mon Sep 17 00:00:00 2001
From: Slava Pestov <spestov@apple.com>
Date: Thu, 2 Mar 2017 23:34:40 -0800
Subject: [PATCH] AST: Targeted fix for conformance lookup issue

When substituting a type like T.A.B where A and B are
associated types and the conformance requirement on T.A
is implied by conformance requirements on T, we would
crash.

The problem is that we have no way of representing an
abstract conformance with nested concrete types.

This patch adds a workaround.

Fixes <rdar://problem/30737546> and
<https://bugs.swift.org/browse/SR-3500>.
---
 lib/AST/SubstitutionMap.cpp                      | 16 +++++++++++++++-
 .../compiler_crashers_2_fixed/0076-sr3500.swift  | 12 ++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 validation-test/compiler_crashers_2_fixed/0076-sr3500.swift

diff --git a/lib/AST/SubstitutionMap.cpp b/lib/AST/SubstitutionMap.cpp
index 7919fe07c9c64..80d87d7a5c9ba 100644
--- a/lib/AST/SubstitutionMap.cpp
+++ b/lib/AST/SubstitutionMap.cpp
@@ -17,6 +17,7 @@
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/SubstitutionMap.h"
 #include "swift/AST/Decl.h"
+#include "swift/AST/Module.h"
 #include "swift/AST/ProtocolConformance.h"
 #include "swift/AST/Types.h"
 
@@ -70,7 +71,8 @@ SubstitutionMap::lookupConformance(CanType type,
   }
 
   // Check if we have substitutions from one of our parent types.
-  return forEachParent(type, [&](CanType parent, AssociatedTypeDecl *assocType)
+  auto result = forEachParent(type,
+    [&](CanType parent, AssociatedTypeDecl *assocType)
       -> Optional<ProtocolConformanceRef> {
 
     auto *parentProto = assocType->getProtocol();
@@ -87,6 +89,18 @@ SubstitutionMap::lookupConformance(CanType type,
 
     return lookupConformance(proto, sub.getConformances());
   });
+
+  // FIXME: Narrow fix for broken conformance lookup
+  if (!result || result->isAbstract()) {
+    auto substTy = type.subst(*this);
+    if (!substTy)
+      return result;
+
+    auto *M = proto->getParentModule();
+    return M->lookupConformance(substTy, proto, nullptr);
+  }
+
+  return result;
 }
 
 void SubstitutionMap::
diff --git a/validation-test/compiler_crashers_2_fixed/0076-sr3500.swift b/validation-test/compiler_crashers_2_fixed/0076-sr3500.swift
new file mode 100644
index 0000000000000..f93111211fcd4
--- /dev/null
+++ b/validation-test/compiler_crashers_2_fixed/0076-sr3500.swift
@@ -0,0 +1,12 @@
+// RUN: %target-swift-frontend %s -emit-ir
+
+protocol A {
+  associatedtype Coordinate: Strideable
+  func doSomething(_: Range<Coordinate>) -> Coordinate.Stride
+}
+
+extension A where Coordinate == Int {
+  func extensionFunc(_ range: Range<Coordinate>) {
+    _ = doSomething(range)
+  }
+}