[rustdoc-json] absolute position of item is hard to get #93524

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1. CraftSpider

   added

   A-rustdoc-jsonArea: Rustdoc JSON backendArea: Rustdoc JSON backend

   C-enhancementCategory: An issue proposing an enhancement or a PR with one.Category: An issue proposing an enhancement or a PR with one.

   on Jan 31, 2022
2. Enselic commented on Feb 8, 2022

   

   Enselic

   on Feb 8, 2022

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   It is not quite that simple unfortunately, because an item can have many "parents". Consider this code insrc/lib.rs:

   mod m {
       pub const C: usize = 7;
   }
   
   pub mod a {
       pub use super::m::C;
   }
   
   pub mod b {
       pub use super::m::C;
   }

   The rustdoc JSON will be (some details omitted):

           "0:4": {
               "id": "0:4",
               "crate_id": 0,
               "name": "C",
               "visibility": "public",
               "kind": "constant",
               "inner": {
                   "type": {
                       "kind": "primitive",
                       "inner": "usize"
                   },
               }
           },
           "0:5": {
               "id": "0:5",
               "crate_id": 0,
               "name": "a",
               "visibility": "public",
               "kind": "module",
               "inner": {
                   "is_crate": false,
                   "items": [
                       "0:4"           <--- Note: Contains C
                   ]
               }
           },
           "0:9": {
               "id": "0:9",
               "crate_id": 0,
               "name": "b",
               "visibility": "public",
               "kind": "module",
               "inner": {
                   "is_crate": false,
                   "items": [
                       "0:4"           <--- Note: Also contains C
                   ]
               }
           },

   So if you were to encounter only "0:4", you would not know what parent is "correct".
3. Urgau commented on Feb 8, 2022

   

   Urgau

   on Feb 8, 2022

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   It is not quite that simple unfortunately, because an item can have many "parents".

   Yes many relative "parents" but there is only one absolute parent. Ex: a struct A is defined in the module my_mod with a re-export from a another module, in this case the parent of A is my_mod and nothing else.
   Here parent should be seeing as where the item was defined. A item can only be defined in one place and so can only have one parent.
4. Enselic commented on Feb 9, 2022

   

   Enselic

   on Feb 9, 2022

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   What you call the "absolute parent" is not always present in the rustdoc JSON output though. For example in the sample code above, because mod m is not pub. I use this command: RUSTDOCFLAGS='-Z unstable-options --output-format json' cargo +nightly doc --lib --no-deps.

   Should we simply omit parent_id in that case? That doesn't seem quite right either.
5. Urgau commented on Feb 9, 2022

   

   Urgau

   on Feb 9, 2022

   Last edited by Urgau

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   What you call the "absolute parent" is not always present in the rustdoc JSON output though.

   This will solved by #93518 who is introducing the StrippedModule item.

   I have already been locally experimenting with #93518 and DefIdTree::parent, and it seems to work (decently) well. I will continue to experiment/test to see the all up and downside.

   👍React with 👍1Reacted by Martin Nordholts