[CSSimplify] Prevent missing call fix from recording fixes while matching types

We need to be very careful while matching types to test whether a
fix is applicable or not to avoid adding extraneous fixes and failing
the path early. This is a temporary workaround, the real fix would
be to let `matchTypes` to propagate `TMF_ApplyingFixes` down.

Resolves: rdar://154010220
Resolves: #82397

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -5365,6 +5365,11 @@ bool ConstraintSystem::repairFailures(
       matchKind = ConstraintKind::Conversion;
     }
 
+    // FIXME: There is currently no easy way to avoid attempting
+    // fixes, matchTypes do not propagate `TMF_ApplyingFix` flag.
+    llvm::SaveAndRestore<ConstraintSystemOptions> options(
+        Options, Options - ConstraintSystemFlags::AllowFixes);
+
     auto result = matchTypes(resultType, dstType, matchKind,
                              TypeMatchFlags::TMF_ApplyingFix, locator);
 

test/Constraints/assignment.swift

@@ -88,3 +88,16 @@ class С_56396 {
     self.callback = callback // expected-error {{cannot assign value of type '(Self) -> Void' to type '(С_56396) -> Void'}}
   }
 }
+
+// https://github.com/swiftlang/swift/issues/82397
+func testFunctionAssignsWithOptionals(fn: @escaping () -> () -> Void) {
+  let _: (() -> () -> Void)? = fn
+  let _: (() -> () -> Void)?? = fn
+
+  class Super {}
+  class Sub: Super {}
+
+  let b: () -> () -> Sub = { { return Sub() } }
+  let _: (() -> () -> Super)? = b
+  let _: (() -> () -> Super)?? = b
+}