std.parseJson

[jwise]

I have recently found myself with cause to parse some ill-formed partial JSON -- a library that we are incrementally converting to Jsonnet was originally parsed by the C preprocessor, and had files like this:

main.jh:

{
  "unit_1": {
#include "unit_1.jh"
  },
  "unit_2": {
#include "unit_2.jh
  },
  ...
}

unit_1.jh:

  "out": {
    ... data ...
  }

I'd like to be able to load a unit_1.jh directly into Jsonnet without invoking an external pass. Obviously, I can't hand it to import, since it's ill-formed. importstr can load it so that I can do extra work on it, but once I have a string, I can't convert it to an object. Really, I'd like to be able to do something like:

eval ("{" + importstr "unit_1.jh" + "}")

Or, even better,

local importjh(f) = eval("{" + importstr f + "}")

though that would require changes along the lines of #196, too.

This is closely related to #460, but maybe more general. One key difference is that #460 wants to be "safe"; in this case, "everybody knows" that any time you type "eval", you deserve whatever happens next 😄 We intend to use this only on trusted JSON databases.

[sbarzowski]

If unit_1.jh is json without outer braces, parseJson (mentioned in #196) would be enough. Or is there some reason to treat it as jsonnet?

[sparkprime]

Yeah I had that thought too.

[jwise]

parseJson would be okay too, but I imagine that eval is probably lower effort to implement -- and works equally well for my application (trusted input).

[sparkprime]

eval is easy to implement but 1) code using it is hard to read 2) any language forcing you to use it for trivial things probably isn't very good. parseJson seems to come up fairly frequently though.

[glerchundi]

Any update on this? Would love to see this implemented!

[sbarzowski]

Funny you ask, yesterday I've just started looking into this again. In go-jsonnet adding it is trivial, but in cpp-jsonnet it requires some effort. I also have a partially implemented pure-jsonnet JSON parser, but it's going to be really slow compared to anything native.

[glerchundi]

Good to hear, thanks for the update!

[sparkprime]

I think vendoring a small json parser into the C++ implementation would be reasonable.

[sbarzowski]

I think we can close it now (06c1ce1).