Add error handling for incorrect activities in Forward mode autodiff #139590
Description
Code
#[autodiff(df, Forward, Dual, Dual)] fn f(x: f32, _y: f32) -> f32 { x }Discussion: https://rust-lang.zulipchat.com/#narrow/channel/182449-t-compiler.2Fhelp/topic/Assistance.20with.20autodiff.20compiler.20panic/with/510644112
Bug repro in enzyme explorer: https://fwd.gymni.ch/rMla2i
Meta
rustc --version --verbose:
rustc --version --verbose rustc 1.85.0-nightly (0aeaa5eb2 2024-12-14) binary: rustc commit-hash: 0aeaa5eb22180fdf12a8489e63c4daa18da6f236 commit-date: 2024-12-14 host: aarch64-apple-darwin release: 1.85.0-nightly LLVM version: 19.1.5 Error output
error: expected 3 activities, but found 2 Backtrace
thread 'rustc' panicked at compiler/rustc_builtin_macros/src/autodiff.rs:506:17: Expected two return types for dual stack backtrace: 0: 0x10b93a3bc - std::backtrace::Backtrace::create::hd5f74c9541fa041c ...