std.json: Adds jsonParse to override parsing behavior #8791
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implementing this was always planned, but its tricky because you need to handle the token lookahead. Trying to do that in a way that isn't a foot-gun for people implementing the trait was too difficult IMO.
I was planning on an eventual overhaul of the token parser, so I had delayed implementing this feature (as it would break everyone's traits).
| @@ -2648,17 +2673,9 @@ pub fn stringify( | |||
| } | |||
| }, | |||
| .Enum => { | |||
| if (comptime std.meta.trait.hasFn("jsonStringify")(T)) { | |||
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only enum/union/struct can have user traits; it makes more sense to keep them here?
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This is exactly why I found it reasonable to move it outside: it stops this check from getting repeated in the code without altering behavior. Since I applied the same reasoning to jsonParse and jsonStringify is effectively its pair I thought it was a good idea to have the same logic applied to it.
| @@ -1708,6 +1708,9 @@ fn parseInternal(comptime T: type, token: Token, tokens: *TokenStream, options: | |||
| } | |||
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| pub fn parse(comptime T: type, tokens: *TokenStream, options: ParseOptions) !T { | |||
| if (comptime std.meta.trait.hasFn("jsonParse")(T)) { | |||
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This will only work at the top level: the internal recursion uses parseInternal.
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Whoops, for all examples I tried I somehow never had one where the root did not have jsonParse implemented. What's stopping us from simply keeping a boolean on TokenStream to know if we need the lookahead or not?
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I have investigated, and the token parser indeed badly needs an overhaul. I couldn't find a simple enough way to get this properly done without a refactor, but I can't do that right now, so for the time being I will close this PR.
std.jsoncurrently has the ability to override serialization behavior by implementingjsonStringify. This is pretty useless, as the other way is impossible. As such I addedjsonParseto override deserialization.I also unified all
jsonStringifys into a single one at the beginning of thestringifyfunction.