Add support for source maps

Hi all,

In PR #56, it was discussed one can modify the EJS source before handing it to ejs.compile(). It works, but has the downside of making the extended error messages (with EJS source and line numbers) hard to read, since all source will probably be presented as one line.

Another solution is to minify the render()'s output, but this may be too expensive. In my benchmarks, using html-minifier, it takes more than 100ms (for my use case, that’s too much).

But I think offering HTML minification as part of EJS is not the way to go either, since it would bloat this wonderful module too much and would not solve the underlying problem with pre-processed source.

What if EJS could accept a source map as part of the compilation and use it to report the right line number and original source? This way, HTML minification could be part of another module, separating concerns.

I’d like to hear you position on this issue: do you think this module should accommodate this use case?

Best regards, Guilherme

[RyanZim]

Thanks for chiming in @sitegui

As things stand now, I would be in favor of closing this.

• @sitegui has found a solution that works for him.
• Someone would need to write the EJS minifier; unless we have a volunteer for that, there is no point discussing this.

@TimothyGu If you feel that line-number error mapping should/could be rewritten, that should be a separate issue. “If it ain’t broke, don’t fix it!” IMO, though.

If someone has something else to add to this discussion, please do so, otherwise, I will probably close in few days.

[v4dkou]

From what I see, to implement source maps, we need to pass this.currentLine to the compiled __append in the scanLine method. Then if we extend this __append method to store an association between the source line number and output lines range, we’ll get something like a source map.

https://github.com/mde/ejs/blob/main/lib/ejs.js#L885 https://github.com/mde/ejs/blob/main/lib/ejs.js#L827