rust-src binary package in Ubuntu Focal armhf

 Rust is a curly-brace, block-structured expression language. It
 visually resembles the C language family, but differs significantly
 in syntactic and semantic details. Its design is oriented toward
 concerns of "programming in the large", that is, of creating and
 maintaining boundaries - both abstract and operational - that
 preserve large-system integrity, availability and concurrency.
 .
 It supports a mixture of imperative procedural, concurrent actor,
 object-oriented and pure functional styles. Rust also supports
 generic programming and meta-programming, in both static and dynamic
 styles.
 .
 This package contains sources of the Rust compiler and standard
 libraries, useful for IDEs and code analysis tools such as Racer.

Source package