[CSSimplify] Delay inout type to pointer conversion until inout is sufficiently resolved

lib/Sema/CSBindings.cpp

@@ -1484,6 +1484,23 @@ PotentialBindings::inferFromRelational(Constraint *constraint) {
         AdjacentVars.insert({typeVar, constraint});
     }
 
+    // Infer a binding from `inout $T <convertible to> Unsafe*Pointer<...>?`.
+    if (first->is<InOutType>() &&
+        first->getInOutObjectType()->isEqual(TypeVar)) {
+      if (auto pointeeTy = second->lookThroughAllOptionalTypes()
+                               ->getAnyPointerElementType()) {
+        if (!pointeeTy->isTypeVariableOrMember()) {
+          // The binding is as a fallback in this case because $T could
+          // also be Array<X> or C-style pointer.
+          if (constraint->getKind() >= ConstraintKind::ArgumentConversion)
+            DelayedBy.push_back(constraint);
+
+          return PotentialBinding(pointeeTy, AllowedBindingKind::Exact,
+                                  constraint);
+        }
+      }
+    }
+
     return std::nullopt;
   }
 

lib/Sema/CSSimplify.cpp

@@ -7683,15 +7683,16 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
           // scalar or array.
           if (auto inoutType1 = dyn_cast<InOutType>(desugar1)) {
             if (!isAutoClosureArgument) {
-              auto inoutBaseType = inoutType1->getInOutObjectType();
+              auto inoutBaseType = getFixedTypeRecursive(
+                  inoutType1->getInOutObjectType(), /*wantRValue=*/true);
 
-              auto baseIsArray =
-                  getFixedTypeRecursive(inoutBaseType, /*wantRValue=*/true)
-                      ->isArrayType();
+              // Wait until the base type of `inout` is sufficiently resolved
+              // before making any assessments regarding conversions.
+              if (inoutBaseType->isTypeVariableOrMember())
+                return formUnsolvedResult();
+
+              auto baseIsArray = inoutBaseType->isArrayType();
 
-              // FIXME: If the base is still a type variable, we can't tell
-              // what to do here. Might have to try \c ArrayToPointer and make
-              // it more robust.
               if (baseIsArray)
                 conversionsOrFixes.push_back(
                     ConversionRestrictionKind::ArrayToPointer);

test/Constraints/optional.swift

@@ -478,20 +478,17 @@ func rdar75146811() {
 
   var arr: [Double]! = []
 
-  test(&arr) // expected-error {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
+  test(&arr) // Ok
   test((&arr)) // expected-error {{'&' may only be used to pass an argument to inout parameter}}
-  // expected-error@-1 {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
-  test(&(arr)) // expected-error {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
+  test(&(arr)) // Ok
 
-  test_tuple(&arr, x: 0) // expected-error {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
+  test_tuple(&arr, x: 0) // Ok
   test_tuple((&arr), x: 0) // expected-error {{'&' may only be used to pass an argument to inout parameter}}
-  // expected-error@-1 {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
-  test_tuple(&(arr), x: 0) // expected-error {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
+  test_tuple(&(arr), x: 0) // Ok
 
-  test_named(x: &arr) // expected-error {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
+  test_named(x: &arr) // Ok
   test_named(x: (&arr)) // expected-error {{'&' may only be used to pass an argument to inout parameter}}
-  // expected-error@-1 {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
-  test_named(x: &(arr)) // expected-error {{cannot convert value of type '[Double]?' to expected argument type 'Double'}}
+  test_named(x: &(arr)) // Ok
 }
 
 // rdar://75514153 - Unable to produce a diagnostic for ambiguities related to use of `nil`

test/Constraints/valid_pointer_conversions.swift

@@ -51,3 +51,21 @@ do {
 func rdar68254165(ptr: UnsafeMutablePointer<Int8>) {
   _ = String(decodingCString: ptr, as: .utf8) // expected-error {{generic parameter 'Encoding' could not be inferred}}
 }
+
+// The base of leading-dot syntax could be inferred through an implicit pointer conversion.
+do {
+  struct S {
+    static var prop = S()
+  }
+
+  func inference_through_optional(_ ptr: UnsafePointer<S>?) {}
+
+  inference_through_optional(&.prop) // Ok
+
+  func inference_through_force_unwrap(name: String) {
+    func test(_: UnsafeMutablePointer<Float>!) {}
+
+    var outputs = [String: [Float]]()
+    test(&outputs[name]!) // Ok
+  }
+}

test/Sema/diag_non_ephemeral.swift

@@ -198,8 +198,10 @@ takesMutableRaw(&ResilientStruct.staticStoredProperty, 5) // expected-error {{ca
 // expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeMutableRawPointer' produces a pointer valid only for the duration of the call to 'takesMutableRaw'}}
 // expected-note@-2 {{use 'withUnsafeMutableBytes' in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 
-// FIXME: This should also produce an error.
-takesMutableRaw(&type(of: topLevelResilientS).staticStoredProperty, 5)
+
+takesMutableRaw(&type(of: topLevelResilientS).staticStoredProperty, 5) // expected-error {{cannot use inout expression here; argument #1 must be a pointer that outlives the call to 'takesMutableRaw'}}
+// expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeMutableRawPointer' produces a pointer valid only for the duration of the call to 'takesMutableRaw'}}
+// expected-note@-2 {{use 'withUnsafeMutableBytes' in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 
 //   - Resilient struct or class bases
 
@@ -221,8 +223,10 @@ takesRaw(&topLevelP.property) // expected-error {{cannot use inout expression he
 // expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeRawPointer' produces a pointer valid only for the duration of the call to 'takesRaw'}}
 // expected-note@-2 {{use 'withUnsafeBytes' in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 
-// FIXME: This should also produce an error.
-takesRaw(&type(of: topLevelP).staticProperty)
+
+takesRaw(&type(of: topLevelP).staticProperty) // expected-error {{cannot use inout expression here; argument #1 must be a pointer that outlives the call to 'takesRaw'}}
+// expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeRawPointer' produces a pointer valid only for the duration of the call to 'takesRaw'}}
+// expected-note@-2 {{use 'withUnsafeBytes' in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 
 takesRaw(&topLevelP[]) // expected-error {{cannot use inout expression here; argument #1 must be a pointer that outlives the call to 'takesRaw'}}
 // expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeRawPointer' produces a pointer valid only for the duration of the call to 'takesRaw'}}

test/Sema/diag_non_ephemeral_warning.swift

@@ -198,8 +198,9 @@ takesMutableRaw(&ResilientStruct.staticStoredProperty, 5) // expected-warning {{
 // expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeMutableRawPointer' produces a pointer valid only for the duration of the call to 'takesMutableRaw'}}
 // expected-note@-2 {{use 'withUnsafeMutableBytes' in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 
-// FIXME: This should also produce a warning.
-takesMutableRaw(&type(of: topLevelResilientS).staticStoredProperty, 5)
+takesMutableRaw(&type(of: topLevelResilientS).staticStoredProperty, 5) // expected-warning {{cannot use inout expression here; argument #1 must be a pointer that outlives the call to 'takesMutableRaw'}}
+// expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeMutableRawPointer' produces a pointer valid only for the duration of the call to 'takesMutableRaw'}}
+// expected-note@-2 {{use 'withUnsafeMutableBytes' in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 
 //   - Resilient struct or class bases
 
@@ -221,8 +222,9 @@ takesRaw(&topLevelP.property) // expected-warning {{cannot use inout expression
 // expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeRawPointer' produces a pointer valid only for the duration of the call to 'takesRaw'}}
 // expected-note@-2 {{use 'withUnsafeBytes' in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 
-// FIXME: This should also produce a warning.
-takesRaw(&type(of: topLevelP).staticProperty)
+takesRaw(&type(of: topLevelP).staticProperty) // expected-warning {{cannot use inout expression here; argument #1 must be a pointer that outlives the call to 'takesRaw'}}
+// expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeRawPointer' produces a pointer valid only for the duration of the call to 'takesRaw'}}
+// expected-note@-2 {{use 'withUnsafeBytes' in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 
 takesRaw(&topLevelP[]) // expected-warning {{cannot use inout expression here; argument #1 must be a pointer that outlives the call to 'takesRaw'}}
 // expected-note@-1 {{implicit argument conversion from 'Int8' to 'UnsafeRawPointer' produces a pointer valid only for the duration of the call to 'takesRaw'}}