[CSDiagnostics] MissingOptionalUnwrapKeyPathFailure to diagnose missing unwrap on base of keypath application

Author: LucianoPAlmeida

lib/Sema/CSDiagnostics.cpp

@@ -6493,3 +6493,19 @@ void MissingRawValueFailure::fixIt(InFlightDiagnostic &diagnostic) const {
 
   diagnostic.fixItInsertAfter(range.End, fix);
 }
+
+bool MissingOptionalUnwrapKeyPathFailure::diagnoseAsError() {
+  emitDiagnostic(diag::optional_not_unwrapped, getFromType(),
+                 getFromType()->lookThroughSingleOptionalType());
+  
+  emitDiagnostic(diag::optional_keypath_application_base)
+      .fixItInsertAfter(getLoc(), "?");
+  emitDiagnostic(diag::unwrap_with_force_value)
+      .fixItInsertAfter(getLoc(), "!");
+  return true;
+}
+
+SourceLoc MissingOptionalUnwrapKeyPathFailure::getLoc() const {
+  auto *SE = castToExpr<SubscriptExpr>(getAnchor());
+  return SE->getBase()->getEndLoc();
+}

lib/Sema/CSDiagnostics.h

@@ -2191,6 +2191,24 @@ class MissingRawValueFailure final : public AbstractRawRepresentableFailure {
   void fixIt(InFlightDiagnostic &diagnostic) const override;
 };
 
+/// Diagnose a key path optional base that should be unwraped in order to 
+/// apply key path subscript.
+///
+/// \code
+/// func f(_ bar: Bar? , keyPath: KeyPath<Bar, Int>) {
+///   bar[keyPath: keyPath]
+/// }
+/// \endcode
+class MissingOptionalUnwrapKeyPathFailure final : public ContextualFailure {
+public:
+  MissingOptionalUnwrapKeyPathFailure(const Solution &solution, Type lhs,
+                                      Type rhs, ConstraintLocator *locator)
+      : ContextualFailure(solution, lhs, rhs, locator) {}
+
+  bool diagnoseAsError() override;
+  SourceLoc getLoc() const override;
+};
+
 } // end namespace constraints
 } // end namespace swift