intra-doc links: `crate::ptr` on a re-export of core::slice is not resolved in alloc

[jyn514]

It's something to do specifically with the re-export because using ptr instead of crate::ptr works, possibly because it's available in both alloc::slice and core::slice.

I don't understand why this is failing :/ the error is being returned directly from rustc_resolve:

$ RUSTDOC_LOG=rustdoc::passes::collect=debug,rustc_resolve=debug xpy test --stage 1 linkchecker library/alloc
: Some(NodeId(101625)), has_generic_args: false }], opt_ns=Some(MacroNS), record_used=true, path_span=library/alloc/src/lib.rs:1:1: 1:1 (#0), crate_lint=No)
2020-08-29T22:46:53.052491Z DEBUG rustc_resolve: resolve_path ident 0 crate#0 Some(NodeId(101624))
2020-08-29T22:46:53.052494Z DEBUG rustc_resolve: resolve_crate_root(crate#0)
2020-08-29T22:46:53.052496Z DEBUG rustc_resolve: resolve_crate_root: not DollarCrate
2020-08-29T22:46:53.052499Z DEBUG rustc_resolve: resolve_crate_root(crate#0): found no mark (ident.span = library/alloc/src/lib.rs:1:1: 1:1 (#0))
2020-08-29T22:46:53.052502Z DEBUG rustc_resolve: resolve_path ident 1 ptr#0 Some(NodeId(101625))
2020-08-29T22:46:53.053654Z DEBUG rustc_resolve: resolve_path(path=[Segment { ident: crate#0, id: Some(NodeId(101626)), has_generic_args: false }, Segment { ident: ptr#0, id
: Some(NodeId(101627)), has_generic_args: false }], opt_ns=Some(TypeNS), record_used=true, path_span=library/alloc/src/lib.rs:1:1: 1:1 (#0), crate_lint=No)
2020-08-29T22:46:53.053666Z DEBUG rustc_resolve: resolve_path ident 0 crate#0 Some(NodeId(101626))
2020-08-29T22:46:53.053669Z DEBUG rustc_resolve: resolve_crate_root(crate#0)
2020-08-29T22:46:53.053671Z DEBUG rustc_resolve: resolve_crate_root: not DollarCrate
2020-08-29T22:46:53.053673Z DEBUG rustc_resolve: resolve_crate_root(crate#0): found no mark (ident.span = library/alloc/src/lib.rs:1:1: 1:1 (#0))
2020-08-29T22:46:53.053677Z DEBUG rustc_resolve: resolve_path ident 1 ptr#0 Some(NodeId(101627))
2020-08-29T22:46:53.054499Z DEBUG rustdoc::passes::collect_intra_doc_links: crate::ptr resolved to Err(()) in namespace TypeNS with parent DefId(1:6606 ~ core[c85e]::slice[0
])
2020-08-29T22:46:53.055390Z  INFO rustdoc::passes::collect_intra_doc_links: ignoring warning from parent crate: unresolved link to `crate::ptr`

In fact if you look at the debug logging it says itself that it's looking at core: parent DefId(1:6606 ~ core[c85e]::slice[0]). Not sure what's going wrong.

It would be great to find an MCVE of this.

Originally posted by @jyn514 in #75932 (comment)

[jyn514]

Direct link to the failing intra-doc link: 6aae4a2#diff-e5a4dbd27d5eadb7a3cf746c396f5420R6430

[jyn514]

Some more test cases from #76235:

std/sync/struct.Arc.html:214: broken link - std/sync/mem::MaybeUninit::method.assume_init
std/sync/struct.Arc.html:238: broken link - std/sync/mem::MaybeUninit::method.assume_init
alloc/sync/struct.Arc.html:214: broken link - alloc/sync/mem::MaybeUninit::method.assume_init
alloc/sync/struct.Arc.html:238: broken link - alloc/sync/mem::MaybeUninit::method.assume_init
thread 'main' panicked at 'found some broken links', src/tools/linkchecker/main.rs:67:9

[jyn514]

GitHub was overeager, this is not fixed, just worked around.