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ReleaseNotes.md

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2021-04-04: rustc 1.39.0 bootstrap

New/interesting supported features since 1.29

  • Basic/minimal constant generics
    • This forced a much-needed internal cleanup of generic/monomorphisation handling
  • Generators (needed for one small bit in librustc_interface)
  • Much better handling of editions and the mess involved around handling different editions across macros
  • By-value trait object methods (lots of hackery here)

Prominent internal changes

  • Type resolution (hir_typeck/expr_cs.cpp) completely reviewed and mostly justified (see Notes/TypecheckIssues.md) to hopefully finally stop typecheck errors being the bane of my existence
  • HIR::TypeRef reworked to actually be a "Ref" (reference counted pointer). This was profiled to save quite a bit of memory via de-duplication and reduction of inline sizes
  • Enum niche optimisation implemented (including a correct implementation of repr(Rust,uNN) layouts
  • Full MIRI constant evaluation (near-complete removal of the HIR::Literal type).
    • Resolved statics and constants are now stored as bytes with relocations
  • proc_macro library expanded to support new features (and allow better testing)
  • minicargo supports overriding parts of crate manifests (as an alternative to doing source patches)
  • minicargo can now handle rustc as well as mrustc
  • Cleaned up handling of hygine (attaching directly to idents)
  • macro_rules handling reworked to pre-calculate looping logic
  • Classification of named patterns into structs and enums deferred until after associated type expansion
  • De-duplication of impl resolution logic for looking up values (for better and more consistent support of impl specialisation)
  • Specialised RcString::ord for interned strings (using a lazily cached ordering) for faster lookups)
  • Explicit MIR-level generation of vtables and drop glue (trans/auto_impls.cpp)

Minor/notable changes

  • Improved macro resolution logic
  • Cleanup to AST path handling
  • Support for one AST path referring to two different items (e.g. a type and a function, via colliding use statements)
  • Unified trait impl lists after HIR generation (to avoid searching n_crates different impl lists)
  • LOTS of usage of TU_MATCH/TU_MATCH_DEF replaced with TU_MATCH_HDRA
  • HIR serialisation reworked to support some encoded structure (for better error diagnosis)
  • Speed up Trans Enumerate by caching paths/types needed by a function