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Support emitting spans when deserializing structures #201
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I've added some more tests and believe this is feature complete. @dtolnay, would you be able to review this PR? There's a quirk when trying to get the start location of a map. For example, given this document... document:
first: 1
second: 2 ... and this struct definition... #[derive(Debug, serde_derive::Deserialize)]
struct Document {
nested: Spanned<Nested>,
}
#[derive(Debug, serde_derive::Deserialize)]
struct Nested {
first: u32,
second: u32,
} ... Our I think this may have something to do with how maps are deserialized and when tokens are consumed, but I don't know how to resolve the issue cleanly. I wrote a doc-test so people are aware of this behaviour and to help detect when it is fixed in the future. |
@dtolnay other than making it compatible with Rust 1.31, is anything else blocking this PR from being merged? |
serde and serde_yaml generate terrible error messages for untagged enums. We can fix this with manual deserialization. Or at least improve it. serde-rs/serde#773 serde-rs/serde#741 dtolnay/serde-yaml#201
This would be great to have! |
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I'd prefer not to build this into serde_yaml. For now I would recommend using a different crate if you need the spans.
Thanks anyway for the PR!
Oh, I see. Thank you for your time :) But is there even a YAML crate out there which supports this? |
Not that I could find. Your best bet is to fork |
Similar to toml-rs/toml-rs#236, serde-rs/json#637, and serde-rs/serde#1811, this provides a mechanism for extracting the source location for a particular value. I've mostly copied the
toml
crate's approach.For more complex cases like mappings and sequences the spans don't look 100% correct (e.g. it may miss a closing
]
or mappings start at: value
instead ofkey: value
), but that may just be because of whereyaml_rust
decides to emit an event or becauseyaml_rust::scanner::Marker
only records where an event starts and not its length.In the long run I'd like to have a common mechanism/protocol for emitting span information in
serde
(outlined here), but in the meantime this should give us a good place to experiment.