[CSSimplify] Remove ad-hoc optional mismatch handling for arguments

Since we have `repairViaOptionalUnwrap`, let's use that to fix
argument/parameter mismatches instead of doing ad-hoc matching.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -4989,8 +4989,18 @@ repairViaOptionalUnwrap(ConstraintSystem &cs, Type fromType, Type toType,
 
     // First, let's check whether it has been determined that
     // it was incorrect to use `?` in this position.
-    if (cs.hasFixFor(cs.getConstraintLocator(subExpr), FixKind::RemoveUnwrap))
+    if (cs.hasFixFor(cs.getConstraintLocator(subExpr), FixKind::RemoveUnwrap)) {
+      if (auto *typeVar =
+              fromType->getOptionalObjectType()->getAs<TypeVariableType>()) {
+        // If the optional chain is invalid let's unwrap optional and
+        // re-introduce the constraint to be solved later once both sides
+        // are sufficiently resolved, this would allow to diagnose not only
+        // the invalid unwrap but an invalid conversion (if any) as well.
+        cs.addConstraint(matchKind, typeVar, toType,
+                         cs.getConstraintLocator(locator));
+      }
       return true;
+    }
 
     auto type = cs.getType(subExpr);
     // If the type of sub-expression is optional, type of the
@@ -5919,43 +5929,6 @@ bool ConstraintSystem::repairFailures(
     if (repairByTreatingRValueAsLValue(lhs, rhs))
       break;
 
-    // If the problem is related to missing unwrap, there is a special
-    // fix for that.
-    if (lhs->getOptionalObjectType() && !rhs->getOptionalObjectType()) {
-      // If this is an attempt to check whether optional conforms to a
-      // particular protocol, let's do that before attempting to force
-      // unwrap the optional.
-      if (hasConversionOrRestriction(ConversionRestrictionKind::Existential))
-        break;
-
-      if (auto *typeVar =
-              lhs->getOptionalObjectType()->getAs<TypeVariableType>()) {
-        auto *argLoc = typeVar->getImpl().getLocator();
-        if (argLoc->directlyAt<OptionalEvaluationExpr>()) {
-          auto OEE = castToExpr<OptionalEvaluationExpr>(argLoc->getAnchor());
-          // If the optional chain in the argument position is invalid
-          // let's unwrap optional and re-introduce the constraint to
-          // be solved later once both sides are sufficiently resolved,
-          // this would allow to diagnose not only the invalid unwrap
-          // but an invalid conversion (if any) as well.
-          if (hasFixFor(getConstraintLocator(OEE->getSubExpr()),
-                        FixKind::RemoveUnwrap)) {
-            addConstraint(matchKind, typeVar, rhs, loc);
-            return true;
-          }
-        }
-      }
-
-      auto result = matchTypes(lhs->getOptionalObjectType(), rhs, matchKind,
-                               TMF_ApplyingFix, locator);
-
-      if (result.isSuccess()) {
-        conversionsOrFixes.push_back(
-            ForceOptional::create(*this, lhs, rhs, loc));
-        break;
-      }
-    }
-
     // If argument in l-value type and parameter is `inout` or a pointer,
     // let's see if it's generic parameter matches and suggest adding explicit
     // `&`.
@@ -6082,7 +6055,7 @@ bool ConstraintSystem::repairFailures(
 
     if (repairViaOptionalUnwrap(*this, lhs, rhs, matchKind, conversionsOrFixes,
                                 locator))
-      break;
+      return true;
 
     {
       auto *calleeLocator = getCalleeLocator(loc);

test/Constraints/if_expr.swift

@@ -705,6 +705,7 @@ func builderInClosure() {
 func testInvalidOptionalChainingInIfContext() {
   let v63796 = 1
   if v63796? {} // expected-error{{cannot use optional chaining on non-optional value of type 'Int'}}
+  // expected-error@-1 {{type 'Int' cannot be used as a boolean; test for '!= 0' instead}}
 }
 
 // https://github.com/swiftlang/swift/issues/79395

test/Constraints/rdar44770297.swift

@@ -10,6 +10,3 @@ func foo<T: P>(_: () throws -> T) -> T.A? { // expected-note {{where 'T' = 'Neve
 
 let _ = foo() {fatalError()} & nil
 // expected-error@-1 {{global function 'foo' requires that 'Never' conform to 'P'}}
-// expected-error@-2 {{value of optional type 'Never.A?' must be unwrapped to a value of type 'Never.A'}}
-// expected-note@-3 {{coalesce using '??' to provide a default when the optional value contains 'nil'}}
-// expected-note@-4 {{force-unwrap using '!' to abort execution if the optional value contains 'nil'}}