rustdoc_json: improve handling of generic args #142502
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rustdoc-json-types is a public (although nightly-only) API. If possible, consider changing |
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Local measurements indicate some sub-1% instruction count improvements, and some max-rss improvements of up to 2%. |
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☔ The latest upstream changes (presumably #142335) made this pull request unmergeable. Please resolve the merge conflicts. |
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Behavioral changes make sense, but all of them needs tests.
They live in tests/rustdoc-json. Sadly, I've not finished the docs for it yet (rust-lang/rustc-dev-guide#2422), but there's a draft here
type/generic_default.rs and gats.rs are probably good examples
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A lot of these are large! Lots of room for improvement in the future.
A path without generic args, like `Reader`, currently has JSON produced
like this:
```
{"path":"Reader","id":286,"args":{"angle_bracketed":{"args":[],"constraints":[]}}}
```
Even though `types::Path::args` is `Option` and allows for "no args",
instead it gets represented as "empty args". (More like `Reader<>` than
`Reader`.)
This is due to a problem in `clean::Path::from_clean`. It only produces
`None` if the path is an empty string. This commit changes it to also
produce `None` if there are no generic args. The example above becomes:
```
{"path":"Reader","id":286,"args":null}
```
I looked at a few examples and saw this reduce the size of the JSON
output by 3-9%.
The commit also adds an assertion that non-final segments don't have any
generics; something the old code was implicitly relying on.
Note: the original sin here is that `clean::PathSegment::args` is not an
`Option`, unlike `{ast,hir}::PathSegment::args`. I want to fix that, but
it can be done separately.
As per the previous commit, generic args here can only appear on the final segment. So make the comments obey that constraint.
They show up in three places: once as `Option<Box<GenericArgs>>`, once
as `Box<GenericArgs>`, and once as `GenericArgs`. The first option is
best. It is more compact because generic args are often missing. This
commit changes the latter two to the former.
Example output, before and after, for the `AssocItemConstraint` change:
```
{"name":"Offset","args":{"angle_bracketed":{"args":[],"constraints":[]}},"binding":{...}}
{"name":"Offset","args":null,"binding":{...}}
```
Example output, before and after, for the `Type::QualifiedPath` change:
```
{"qualified_path":{"name":"Offset","args":{"angle_bracketed":{"args":[],"constraints":[]}}, ...}}
{"qualified_path":{"name":"Offset","args":null, ...}}
```
This reduces JSON output size, but not by much (e.g. 0.5%), because
`AssocItemConstraint` and `Type::QualifiedPath` are uncommon.
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These commits modify Please ensure that if you've changed the output:
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I added a test as a separate commit early in the sequence, so the changes to @rustbot ready |
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This PR fixes some inconsistencies and inefficiencies in how generic args are handled by rustdoc-json-types.
r? @aDotInTheVoid