2021 H2 static Python roadmap

This issue is a broad roadmap covering the static compiler, module loader, type checker, runtime, JIT, and performance work rather than one scoped change. Start by selecting a single priority bullet and locating its relevant subsystem; completion should be defined by that bullet's specific behavior and validation, not by the full roadmap.

Usability

• [P0] Make static python consumable easily for any Cinder user
  • Module loader in cinder
  • Consolidate rewriter logic into static compiler (out of strict modules)
  • minimum runtime version for static pycs
• [P0] Make static python type checker run as a linter
• [P0] Fix module dependency tracking for pyc invalidation
• [P1] Support Enums defined in static modules
• [P1] Expand Static Python reference guide
  • How to improve perf: primitives, CheckedDict...
  • Things that aren’t supported: multiple inheritance, metaclasses...
  • Gotchas: cbool comparison results
• [P1] Don’t JIT all static functions
  • As we adopt more code into Static Python, not all static functions will be hot enough to deserve JIT, this should be left up to the JIT list to determine.
• [P1] support prod_assert
• [P1] support primitive floats
• [P1] cross-module import always sees consistent (DeclarationVisit only) view of imported module types
• [P1] fix patching of static functions with compatible but keyword-requiring signatures
• [P2] improve type inference of primitive int literals

Performance

• [P0] CheckedList
• [P0] Optimize calls to types
• [P0] Improved descriptor support:
  • Properties
  • Cached properties
  • class methods
• [P1] Primitives in method calls
• [P1] Primitives in type calls
• [P1] More typed built-in methods
• [P1] Dataclass intrinsic
• [P1] Run declaration visitor on nonstatic dependency code and stubs so we can generate invokes against them
  • make sure the failure mode is appropriate Python error, not crash
  • also emit CAST on return value (helps with narrowing and Pyre compat for usability)
• [P1] Support for runtime-checking small unions
• [P1] avoid checking types of default argument values
• [P1] return type of async functions
  • type-specialized await?
  • eager evaluation?
• [P1] type-preserving user-defined decorators (util.etc, statsd.timer)
• [P1] Declarable Exact types
  • Unlocks more non-GC containers, can declare they contain only Exact[str], which is non-GC
  • Unlocks other optimizations and statically known types also, subclasses of Python builtins can do crazy things
• [P2] inlining decorators at compile time
• [P2] Fixed size arrays
• [P2] Perhaps some exploratory work around object lifetimes? Would be great to get some objects out of the GC.
  • Multiple return values that box to tuples but don’t allocate might be something slightly related