errdefer in json.parseInternal causes lots of code generation

[leroycep]

Specifically, this errdefer here:

zig/lib/std/json.zig

Lines 1443 to 1449 in f2d3266

	errdefer {
	inline for (structInfo.fields) |field, i| {
	if (fields_seen[i]) {
	parseFree(field.field_type, @field(r, field.name), options);
	}
	}
	}

            errdefer {
                inline for (structInfo.fields) |field, i| {
                    if (fields_seen[i]) {
                        parseFree(field.field_type, @field(r, field.name), options);
                    }
                }
            }

Later, there is an inline loop for checking if the JSON key matches any of the fields. Inside that inline loop it calls try parse(...).

When I add some @compileLog statements inside the errdefer's inline loop and try to parse this glTF struct, it logs over 5000 calls to the @compileLog statement.

Fixes

• Remove the errdefer and manually catch the error
  • https://github.com/leroycep/gltf-zig/blob/master/json.zig#L1516-L1561
  • While I was implementing this fix I also added an explicit error type to the json.parse function
  • This fix reduced the 5000 calls to less than 500 calls
• Make errdefer smart enough to avoid generating this code O(n^2) times
  • The code to catch the error only need to be generated once in this case. Not sure if this is true all cases like this.

[LemonBoy]

This is #283.

[yurapyon]

Slightly off topic, but I was getting some issues trying to use json.parse on a recursive data structure.
The compiler was saying it couldn't infer the type of the error returned from json.parse.
I was gonna try adding the error type explicitly myself to make sure that fixes it but. yeah 👍

[andrewrk]

This is #283.

☝️

This will be solved in stage2 only.