Replace all const evaluation with miri by oli-obk · Pull Request #46882 · rust-l...

oli-obk commented on Dec 21, 2017 •

• error reporting in constants prints a stacktrace through all called const fns
• Trivial constant propagation and folding in MIR (always active, irrelevant of the optimization level)
• can now use floating constants in patterns (previously only floating point literals were allowed)
  • the future compat lint is still produced for both cases
• can index into constant arrays during const eval (previously feature gated)
• can create a constant union value with field a and read from field b
• can dereference references into constants
• can create references inside constants (const X: &u32 = &22)
• Tuple struct constructors can be used in constants
• regression in const eval errors spans (some of these need improvements in mir debug info)
• can cast floats to ints and vice versa (in constants, and even nan/inf constants)
• Mir dump prints false/true instead of 0u8/1u8
• 1i8 >> [8][0] does not lint about exceeding bitshifts anymore.
  • Needs const propagation across projections
• foo[I] produces a const eval lint if foo: [T; N] and N < I
  • Essentially all builtin panics produce lints if they can be statically proven to trigger at runtime. This is on a best effort basis, so there might be some complex cases that don't trigger. (The runtime panic stays there, irrelevant of whether the lint is produced or not)
• can use unions to implement transmute for Copy types in constants without a feature gate. With all the greatness and nasal demons that come with this.
• can convert integers to &'static T in constants (useful for embedded)

fixes #34997 (stack overflow with many constants)
fixes #25574 (deref byte strings in patterns)
fixes #27918 (broken mir ICE)
fixes #46114 (ICE on struct constructors in patterns)
fixes #37448 (SomeStruct { foo } as SomeStruct)
fixes #43754 (return in const fn)
fixes #41898 (tuple struct constructors)
fixes #31364 (infinite recursion with const fn, fixed by miri's recursion limit)
closes #29947 (const indexing stabilization)
fixes #45044 (pattern matching repeat expressions)
fixes #47971 (ICE on const fn + references)
fixes #48081 (ICE on cyclic assoc const error)
fixes #48746 (nonhelpful error message with unions)

r? @eddyb

even though 1k loc are added in tests, this PR reduces the loc in this repository by 700