[dannote]

Gaps found while rewriting Figler's defrust code in plain Elixir style: comprehensions, Enum.reduce, Map/MapSet, list patterns, []/%{}, and interpolation instead of .iter(), HashMap::new(), deref, and ref.

• Collection basics lower onto Rust's collections. This covers:
  • Map.update/4, which matches the present value;
  • List.replace_at/3;
  • Enum.sort/1 on ordered lists;
  • MapSet.new/1 of listed items (HashSet::from);
  • String.downcase/1 and String.upcase/1;
  • x in [literals], which becomes an array check;
  • comparisons with [], %{}, "", and nil, which become is_empty() and is_some()/is_none().
• Updates happen in place. ++ and Map.update grow an owned list or map instead of cloning it. A for … reduce: with one variable clause names its accumulator after that variable and annotates its type.
• Borrowed values are read, not moved. This applies to:
  • copy items a slice lends;
  • values bound by a pattern on a reference, in comparisons, and/or, and if;
  • an option field reached through a reference, which is matched by reference;
  • a list held by an earlier generator's item, which a nested generator iterates;
  • a list of tuples still in use, which a comprehension reads by reference instead of cloning each item.
• Typing is more complete.
  • Branching expressions, comprehensions through every generator, block bindings in order, reductions, indexing, and nested aliases are typed.
  • A binding keeps the option type its right-hand side gives; this previously produced a double .as_ref().
  • A tuple destructured from a fallible call has typed elements.
  • Counts take the integer type expected of them.
• Desugaring covers more forms.
  • String interpolation becomes format!.
  • A multi-generator for … reduce: becomes Enum.reduce over a comprehension.
  • An irrefutable function argument is bound with =.
• Rendering fixes.
  • A list literal passed for a slice is &[..], not &vec![..].
  • An untyped %{} is HashMap::new().
  • A string-literal key is passed as the &str it already is.
  • A range bound that can fail propagates its error.
  • A range used as a method receiver is parenthesized. It used to render as 1..=n.into_iter(), which doesn't compile.

mix ci passes (920 tests). With this branch, Figler regenerates clippy-clean (-D warnings), and its tests pass apart from the package test, which can't build a Hex package while dependencies are local paths.