eclipse-aascw / aas-core-codegen / 34782402679

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Compose the Go XML serialization (#689)

Write-side dual of #688, as #687 was of #686 in C#.

Measured on the AAS meta-model fixture, the serialization region of
``xmlization.go`` goes 11,080 -> 4,727 lines (-57%), and the file as
a whole 16,692 -> 10,330. ``writeExtensionAsSequence`` and its six
properties go 180 -> 69 lines.

Everything is written through one shape,
``func(encoder, value T) error``. A stringification, a class's own
``write<X>AsSequence`` and the generated item, list and tuple writers
all have it, so ``writeElement`` -- which frames an XML element around
a value written that way -- is the only writer a property needs,
whatever kind of value it holds. What is left per property is that one
call and a decision on presence:

    err = finishProperty(
        "SemanticID()",
        writeOptionalInstance(
            encoder,
            "semanticId",
            that.SemanticID(),
            writeReferenceAsSequence,
        ),
    )
    if err != nil {
        return
    }

``finishProperty`` takes the *result* of the write rather than the write
itself -- the same trick as the read side's ``readOptional``, since Go
evaluates the argument first -- so one function concludes every
property, prepending the getter to the path of the error.

Mind that the getter is spelled out as it is in Go, ``SemanticID()`` and
not ``semanticId``, since a serialization error renders its path through
``aasreporting.ToGolangPath``, while the de-serialization prepends
the XML name, its errors being XPaths. Go has no ``nameof``.

The ``writeOptional*`` family has one member per way Go spells an
optional, each named after that spelling, as the check for the presence
is the only thing which differs between them: a pointer to the value
(``writeOptionalPointer``: a scalar, an enumeration, a tuple), a value
which is nil on its own (``writeOptionalInstance``: an instance, or
a named union, which is a pointer to a struct) and a slice
(``writeOptionalSlice``: a list, ... (continued)

232 of 238 new or added lines in 1 file covered. (97.48%)

33977 of 39839 relevant lines covered (85.29%)

2.56 hits per line