Rustdoc regression in synstructure: error[E0275]: overflow evaluating the requirement `alloc::raw_vec::RawVec<(syn::Lifetime, syn::token::Add)>: std::marker::Unpin`

[SimonSapin]

In a minified package:

[package]
name = "foo"
version = "0.0.0"

[dependencies]
syn = { version = "=0.15.38", features = ["full"] }
synstructure = "=0.10.2"

Running rustup run --install nightly-2019-06-21 cargo doc completes successfully, but rustup run --install nightly-2019-06-22 cargo doc causes the error below. Note that cargo build or cargo check succeeds with either version.

Regression range: 1d9981f...929b48e. #60293 is in the range and looks relevant. CC @nagisa, @eddyb

error[E0275]: overflow evaluating the requirement `alloc::raw_vec::RawVec<(syn::Lifetime, syn::token::Add)>: std::marker::Unpin`
  |
  = help: consider adding a `#![recursion_limit="128"]` attribute to your crate
  = note: required because it appears within the type `std::vec::Vec<(syn::Lifetime, syn::token::Add)>`
  = note: required because it appears within the type `syn::punctuated::Punctuated<syn::Lifetime, syn::token::Add>`
  = note: required because it appears within the type `syn::LifetimeDef`
  = note: required because it appears within the type `(syn::LifetimeDef, syn::token::Comma)`
  = note: required because it appears within the type `*const (syn::LifetimeDef, syn::token::Comma)`
  = note: required because it appears within the type `std::ptr::Unique<(syn::LifetimeDef, syn::token::Comma)>`
  = note: required because it appears within the type `alloc::raw_vec::RawVec<(syn::LifetimeDef, syn::token::Comma)>`
  = note: required because it appears within the type `std::vec::Vec<(syn::LifetimeDef, syn::token::Comma)>`
  = note: required because it appears within the type `syn::punctuated::Punctuated<syn::LifetimeDef, syn::token::Comma>`
  = note: required because it appears within the type `syn::BoundLifetimes`
  = note: required because it appears within the type `std::option::Option<syn::BoundLifetimes>`
  = note: required because it appears within the type `syn::PredicateType`
  = note: required because it appears within the type `syn::WherePredicate`
  = note: required because it appears within the type `(syn::WherePredicate, syn::token::Comma)`
  = note: required because it appears within the type `*const (syn::WherePredicate, syn::token::Comma)`
  = note: required because it appears within the type `std::ptr::Unique<(syn::WherePredicate, syn::token::Comma)>`
  = note: required because it appears within the type `alloc::raw_vec::RawVec<(syn::WherePredicate, syn::token::Comma)>`
  = note: required because it appears within the type `std::vec::Vec<(syn::WherePredicate, syn::token::Comma)>`
  = note: required because it appears within the type `syn::punctuated::Punctuated<syn::WherePredicate, syn::token::Comma>`
  = note: required because it appears within the type `syn::WhereClause`
  = note: required because it appears within the type `std::option::Option<syn::WhereClause>`
  = note: required because it appears within the type `syn::Generics`
  = note: required because it appears within the type `syn::ItemType`
  = note: required because it appears within the type `syn::Item`
  = note: required because it appears within the type `syn::Stmt`
  = note: required because it appears within the type `*const syn::Stmt`
  = note: required because it appears within the type `std::ptr::Unique<syn::Stmt>`
  = note: required because it appears within the type `alloc::raw_vec::RawVec<syn::Stmt>`
  = note: required because it appears within the type `std::vec::Vec<syn::Stmt>`
  = note: required because it appears within the type `syn::Block`
  = note: required because it appears within the type `syn::ExprIf`
  = note: required because it appears within the type `syn::Expr`
  = note: required because it appears within the type `syn::TypeArray`
  = note: required because it appears within the type `syn::Type`
  = note: required because it appears within the type `syn::GenericArgument`
  = note: required because it appears within the type `(syn::GenericArgument, syn::token::Comma)`
  = note: required because it appears within the type `*const (syn::GenericArgument, syn::token::Comma)`
  = note: required because it appears within the type `std::ptr::Unique<(syn::GenericArgument, syn::token::Comma)>`
  = note: required because it appears within the type `alloc::raw_vec::RawVec<(syn::GenericArgument, syn::token::Comma)>`
  = note: required because it appears within the type `std::vec::Vec<(syn::GenericArgument, syn::token::Comma)>`
  = note: required because it appears within the type `syn::punctuated::Punctuated<syn::GenericArgument, syn::token::Comma>`
  = note: required because it appears within the type `syn::AngleBracketedGenericArguments`
  = note: required because it appears within the type `syn::PathArguments`
  = note: required because it appears within the type `syn::PathSegment`
  = note: required because it appears within the type `(syn::PathSegment, syn::token::Colon2)`
  = note: required because it appears within the type `*const (syn::PathSegment, syn::token::Colon2)`
  = note: required because it appears within the type `std::ptr::Unique<(syn::PathSegment, syn::token::Colon2)>`
  = note: required because it appears within the type `alloc::raw_vec::RawVec<(syn::PathSegment, syn::token::Colon2)>`
  = note: required because it appears within the type `std::vec::Vec<(syn::PathSegment, syn::token::Colon2)>`
  = note: required because it appears within the type `syn::punctuated::Punctuated<syn::PathSegment, syn::token::Colon2>`
  = note: required because it appears within the type `syn::Path`
  = note: required because it appears within the type `syn::Attribute`
  = note: required because it appears within the type `*const syn::Attribute`
  = note: required because it appears within the type `std::ptr::Unique<syn::Attribute>`
  = note: required because it appears within the type `alloc::raw_vec::RawVec<syn::Attribute>`
  = note: required because it appears within the type `std::vec::Vec<syn::Attribute>`
  = note: required because it appears within the type `syn::TypeParam`
  = note: required because it appears within the type `syn::GenericParam`
  = note: required because it appears within the type `*const syn::GenericParam`
  = note: required because it appears within the type `std::ptr::Unique<syn::GenericParam>`
  = note: required because it appears within the type `alloc::raw_vec::RawVec<syn::GenericParam>`
  = note: required because it appears within the type `std::vec::Vec<syn::GenericParam>`
  = note: required because it appears within the type `Structure<'a>`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0275`.
error: Could not document `synstructure`.

[nagisa]

Duplicate of #62059. Thanks.