[CSApply] Mark self parameter as inout when base/self match on deep equality

If type equality check fails we need to check whether the types
are the same with deep equality restriction since `any Sendable`
to `Any` conversion is now supported in generic argument positions
of @preconcurrency declarations. i.e. referencing a member on
`[any Sendable]` if member declared in an extension that expects
`Element` to be equal to `Any`.

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -1846,6 +1846,9 @@ class Solution {
   /// locator.
   ArgumentList *getArgumentList(ConstraintLocator *locator) const;
 
+  std::optional<ConversionRestrictionKind>
+  getConversionRestriction(CanType type1, CanType type2) const;
+
   SWIFT_DEBUG_DUMP;
 
   /// Dump this solution.

lib/Sema/CSApply.cpp

@@ -1716,7 +1716,16 @@ namespace {
         // pass it as an inout qualified type.
         auto selfParamTy = isDynamic ? selfTy : containerTy;
 
-        if (selfTy->isEqual(baseTy))
+        // If type equality check fails we need to check whether the types
+        // are the same with deep equality restriction since `any Sendable`
+        // to `Any` conversion is now supported in generic argument positions
+        // of @preconcurrency declarations. i.e. referencing a member on
+        // `[any Sendable]` if member declared in an extension that expects
+        // `Element` to be equal to `Any`.
+        if (selfTy->isEqual(baseTy) ||
+            solution.getConversionRestriction(baseTy->getCanonicalType(),
+                                              selfTy->getCanonicalType()) ==
+                ConversionRestrictionKind::DeepEquality)
           if (cs.getType(base)->is<LValueType>())
             selfParamTy = InOutType::get(selfTy);
 

lib/Sema/ConstraintSystem.cpp

@@ -3966,6 +3966,14 @@ ArgumentList *Solution::getArgumentList(ConstraintLocator *locator) const {
   return nullptr;
 }
 
+std::optional<ConversionRestrictionKind>
+Solution::getConversionRestriction(CanType type1, CanType type2) const {
+  auto restriction = ConstraintRestrictions.find({type1, type2});
+  if (restriction != ConstraintRestrictions.end())
+    return restriction->second;
+  return std::nullopt;
+}
+
 #ifndef NDEBUG
 /// Given an apply expr, returns true if it is expected to have a direct callee
 /// overload, resolvable using `getChoiceFor`. Otherwise, returns false.