1. Bug fixes

Elixir

• [Kernel] Improve the performance of the type system when working with large unions of open maps
• [Kernel] Do not crash on map types with struct keys when performing type operations
• [Kernel] Mark the outcome of bitstring types as dynamic
• [Kernel] <<expr::bitstring>> will have type binary instead of bitstring if expr is a binary
• [Kernel] Do not crash on conditional variables when calling a function on a module which is represented by a variable

I am keeping it all in the same thread as we only had bug fixes.

Thanks for another awesome release and congratulations on 15 amazing years!!

I just finished upgrading a rather big project to 1.19.5 and resolving all warnings. After setting the elixir version to 1.20.0-rc.1 and running mix.compile the compiler revealed many new warnings

• Found a lot of unused required modules. Mostly Logger and Ecto.Query (TIL you don’t need to require the Logger to make use of Logger.metadata)

• Possible false positive or future deprecation? This warning was emitted, but pinning the variable here has no effect aside from removing the warning

  warning: the variable "chunk_size" is accessed inside size(...) of a bitstring but it was defined outside of the match. You must precede it with the pin operator
      │
  118 │     <<chunk::binary-size(chunk_size), rest::binary>> = binary
  

• It found a couple of interesting, unused function clauses, similar to the cases below. In this particular case it was fine, but there are some cases where I cannot figure out the reason. Still a great addition to the compiler

  current = Enum.at(search_results, current_index)
  highlight_term(current.sentence_text, current)}
  

       warning: this clause of defp highlight_term/2 is never used
       │
   194 │   defp highlight_term(text, nil), do: text
  

• In this particular case it didn’t complain about the fact that we (accidentally) assumed that uri.query is a map, but we’re trying to pass a map to URI.decode_query. Still a great find

       warning: incompatible types given to URI.decode_query/1:
  
           URI.decode_query(query)
  
       given types:
  
           dynamic(map())
  
       but expected one of:
  
           binary()
  
       where "query" was given the type:
  
           # type: dynamic(map())
           # from: my_code.ex:187:33
           is_map(query)
  
       typing violation found at:
       │
   188 │            %{"latency" => latency_raw} <- URI.decode_query(query),
  

      uri = URI.parse(url)
  
      latency =
        with %{query: query} when is_map(query) <- uri,
             %{"latency" => latency_raw} <- URI.decode_query(query),
             {latency, ""} <- Integer.parse(latency_raw) do
  
  

I’ve also measured the performance of the compilation of this project a bit. ~190 dependencies and +800 files. Overall very happy with the results and MIX_OS_DEPS_COMPILE_PARTITION_COUNT is a blessing for sure
deps = mix deps.compile
project = mix compile