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core: Fail with a better error message when list_dir gets an empty path

(Yes, this did happen in real life...)
testsuite: Add a test for listing the root directory...

...and don't treat Path("/") like Path("").
auto merge of #6687 : catamorphism/rust/list_dir_empty, r=catamorphism

r? @brson (Yes, this did happen in real life...)
Mark &mut parameters as noalias
rustdoc: properly nest markup within enum variant lists (fixes #6605)

This indents all but the first line of multi-line annotations for
individual enum variants with four spaces so that pandoc will
recognize everything as belonging to the same list item.

Since that introduces `<p>` tags for some list items, I've gone ahead
and inserted blank lines after each list item so that consistently
get `<p>` tags for all `<li>`s documenting variants. It's a bit less
compact now but still tolerable, I think.
auto merge of #6742 : Aatch/rust/mut-noalias, r=thestinger

This marks `&mut` function arguments with the `noalias` attribute. Since the borrow checker enforces this property, this is worth doing.

I'm not sure if the place I'm doing it in is ideal, but it generates the correct code.

Closes #6350
Add documentation for libstd/bool.rs.

There was some before, but now we have a big header, as well as
lots of individual bits of documentation.
auto merge of #6700 : ben0x539/rust/nestvariantdocs, r=thestinger

This indents all but the first line of multi-line annotations for individual enum variants with four spaces so that pandoc will recognize everything as belonging to the same list item.

Since that introduces `<p>` tags for some list items, I've gone ahead and inserted blank lines after each list item so that consistently get `<p>` tags for all `<li>`s documenting variants. It's a bit less compact now but still tolerable, I think.
auto merge of #6748 : steveklabnik/rust/bool_docs, r=thestinger

There was some before, but now we have a big header, as well as
lots of individual bits of documentation.
auto merge of #6719 : kud1ing/rust/rustc_w, r=bstrie

Fixes #6697
Change how the input from rusti is formatted to allow duplicate definitions
Change the generic 'print' function to 'pp' for rusti
Keep a history of assignments in rusti