Improve the check for serialized index version

[crystalfp]

In lunr.Index.load() the version of the loaded index elicits only a warning if the two versions are different. Instead I think lunr.Index.load() should throw an error if the major version differs, output a warning if the minor version differs and display nothing if only the patch level differs (Semantic Versioning docet).

Just to be prepared for the future I added the following lines in my application as a workaround:

        // The index data is read in the data variable
    const serializedIndex = JSON.parse(data);
    const fileVersion = serializedIndex.version.split(".");
    const lunrVersion = lunr.version.split(".");
    if(fileVersion[0] != lunrVersion[0]) throw Error("Saved index major version mismatch");

    lunr.multiLanguage('en', 'it');
    fullTextIndex = lunr.Index.load(serializedIndex);

[olivernn]

The version check is very basic.

I want the schema for the serialised index to be defined outside of Lunr. This is so that the index can be generated without Lunr and a JavaScript runtime.

I'm mostly happy with the current schema, I just need to decide on how to version it, semantic versioning doesn't really make sense for a data format. Once I do that the current version field will be deprecated. At that point if the schema version does not exactly match what the version of lunr understands it should just fail hard.

[crystalfp]

OK, understand.

So do you think it is a "future oriented" move to wrap the Index.load() in a try/catch block and regenerate the index (instead of loading it) if the load fails? Thanks!

[olivernn]

When there is a real schema version, I would imagine that Lunr will just throw if there is a mismatch. You can certainly catch that and re-generate the index. I do not know what the specific error will be yet though.