Merge pull request #61063 from slavapestov/sil-function-type-coroutine

SIL: Use the right generic signature for computing SIL function type for coroutine accessors

Author: slavapestov

lib/SIL/IR/SILFunctionType.cpp

@@ -1960,9 +1960,12 @@ static CanSILFunctionType getSILFunctionType(
 
     if (reqtSubs) {
       valueType = valueType.subst(*reqtSubs);
+      coroutineSubstYieldType = valueType->getReducedType(
+          genericSig);
+    } else {
+      coroutineSubstYieldType = valueType->getReducedType(
+          accessor->getGenericSignature());
     }
-
-    coroutineSubstYieldType = valueType->getReducedType(genericSig);
   }
 
   bool shouldBuildSubstFunctionType = [&]{

test/SILGen/constrained_extensions.swift

@@ -227,3 +227,16 @@ func referenceNestedTypes() {
   _ = Array<AnyObject>.NestedClass()
   _ = Array<AnyObject>.DerivedClass()
 }
+
+struct S<T> {
+  struct X {}
+}
+
+// CHECK-LABEL: sil hidden [ossa] @$s22constrained_extensions1SVAASiRszlEyAC1XVySi_GSicir : $@yield_once @convention(method) (Int, S<Int>) -> @yields S<Int>.X
+extension S<Int> {
+  subscript(index:Int) -> X {
+    _read {
+      fatalError()
+    }
+  }
+}