document when the values of default type parameters are checked for wf and other conditions

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Documentation
Clarity
Mostly clear
Activity status
Stale
Tech stack
rust
Domain
documentation

Research direction

Read Rust issue #61631 and the linked comment first, including its references, to understand the agreed rule for checking default type parameters. Find the relevant Rust Reference section for generic or type parameters and document when the default is checked for well-formedness and related conditions, including the case where it contains another parameter.

Written by the indexing model from the issue text.

Description

A-types

In https://github.com/rust-lang/rust/issues/61631 there is significant confusion concerning when the default value for a type parameter should be checked for consistency. I left a comment here explaining the rule that we arrived at (with some links for more details) -- the short version is that if you have struct Foo<A, B = Default>, then the type Default is only checked for WF and so forth if it does not contain any other parameters (e.g., A). I don't think this rule is in the reference but we should write it up.

Dominant language
Rust
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Forks
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Merged PRs (30d)
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