verify(ApprovalWriter, Options) gives build failure

[claremacrae]

I've been updating ApprovalTests.cpp.Qt to use the latest ApprovalTests.cpp.

This is the code that now does not compile, once I wrap the reporter in Options:

    inline void verifyQImage(
        const QImage& image,
        const ApprovalTests::Reporter& reporter = ApprovalTests::DiffReporter())
    {
        QImageApprovalWriter image_writer(image);
        ApprovalTests::Approvals::verify(image_writer, ApprovalTests::Options(reporter));
    }

where QImageApprovalWriter implements ApprovalTests::ApprovalWriter

The error output is:

In file included from /Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/tests/Catch2_Tests/ApprovalsQtTests.cpp:4:
In file included from /Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/ApprovalTestsQt/../ApprovalTestsQt/ApprovalsQt.h:4:
In file included from /Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/ApprovalTestsQt/../ApprovalTestsQt/integrations/LoadApprovals.h:16:
In file included from /Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/third_party/approval_tests_cpp/ApprovalTests.hpp:1:
/Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/third_party/approval_tests_cpp/ApprovalTests.v.8.7.0.hpp:3216:13: error: type 'ApprovalTests::Options' does not provide a call operator
            converter(contents, s);
            ^~~~~~~~~
/Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/ApprovalTestsQt/../ApprovalTestsQt/ApprovalsQt.h:15:35: 
note: in instantiation of function template specialization 'ApprovalTests::TApprovals<ApprovalTests::ToStringCompileTimeOptions<ApprovalTests::StringMaker> >::verify<ApprovalTestsQt::QImageApprovalWriter, ApprovalTests::Options, void>' requested here
        ApprovalTests::Approvals::verify(image_writer, ApprovalTests::Options(reporter));
                                  ^
In file included from /Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/tests/Catch2_Tests/ApprovalsQtTests.cpp:4:
In file included from /Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/ApprovalTestsQt/../ApprovalTestsQt/ApprovalsQt.h:4:
In file included from /Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/ApprovalTestsQt/../ApprovalTestsQt/integrations/LoadApprovals.h:16:
In file included from /Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/third_party/approval_tests_cpp/ApprovalTests.hpp:1:
/Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/third_party/approval_tests_cpp/ApprovalTests.v.8.7.0.hpp:3216:13: 
error: type 'ApprovalTests::Options' does not provide a call operator
            converter(contents, s);
            ^~~~~~~~~
/Users/clare/Documents/develop/ApprovalTests/ApprovalTests.cpp.Qt/ApprovalTestsQt/../ApprovalTestsQt/ApprovalsQt.h:23:35: 
note: in instantiation of function template specialization 'ApprovalTests::TApprovals<ApprovalTests::ToStringCompileTimeOptions<ApprovalTests::StringMaker> >::verify<ApprovalTestsQt::QTableViewWriter, ApprovalTests::Options, void>' requested here
        ApprovalTests::Approvals::verify(table_writer, ApprovalTests::Options(reporter));
                                  ^

This is supposed to call this method:

        // Note that this overload ignores any scrubber in options
        static void verify(const ApprovalWriter& writer,
                           const Options& options = Options())
        {
            FileApprover::verify(*getDefaultNamer(), writer, options.getReporter());
        }

But instead this method gets selected:

        template <typename T,
                  typename Function,
                  typename = Detail::EnableIfNotDerivedFromReporter<Function>>
        static void
        verify(const T& contents, Function converter, const Options& options = Options())
        {
            std::stringstream s;
            converter(contents, s);
            verify(s.str(), options);
        }

And the code attempts to call options(contents, s) which really doesn't have a call operator.

[claremacrae]

When building against 8.7.0, this change fixes the build:

        template <typename T,
                  typename Function,
+                 typename = IsNotDerivedFromWriter<T>,
                  typename = Detail::EnableIfNotDerivedFromReporter<Function>>
        static void
        verify(const T& contents, Function converter, const Options& options = Options())
        {
            std::stringstream s;
            converter(contents, s);
            verify(s.str(), options);
        }

In 10.0.0 we removed typename = Detail::EnableIfNotDerivedFromReporter<Function> - but the extra IsNotDerivedFromWriter is still required.

The problem only occurs once Reporter arguments are changed to Options.

If Reporter is passed in, there is no ambiguity. I think this is because the new custom ToString mechanism was only added to the new overloads that take Options, and not to the deprecated Reporter-based methods.

[claremacrae]

We do have tests for custom reporters, and we have an ExistingFileWriter (or similar), so I'm unsure what it is about the code in ApprovalTests.cpp.Qt that triggers this scenario...

[claremacrae]

I realise that I will in due course want to update this method so its Reporter argument becomes Options... For now, I wanted to make the smallest changes possible.

    inline void verifyQImage(
        const QImage& image,
        const ApprovalTests::Reporter& reporter = ApprovalTests::DiffReporter())
    {
        QImageApprovalWriter image_writer(image);
        ApprovalTests::Approvals::verify(image_writer, ApprovalTests::Options(reporter));
    }

[claremacrae]

An alternative fix is to say that the Function type is not Options - which matches the previous constraint that Function was not derived from Reporter...

[claremacrae]

This is now fixed - I'll close the issue when we release.

[claremacrae]

This is in the 10.0.1 release, about to be completed