Panic at map_clone.rs:39

[mmstick]

• clippy: commit cd9044
• rustc: nightly as of 2018-06-20

Trying to use clippy on distinst, and getting the following panic:

thread 'main' panicked at 'index out of bounds: the len is 0 but the index is 0', clippy_lints/src/map_clone.rs:39:52
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:515
   6: std::panicking::continue_panic_fmt
             at libstd/panicking.rs:426
   7: rust_begin_unwind
             at libstd/panicking.rs:337
   8: core::panicking::panic_fmt
             at libcore/panicking.rs:92
   9: core::panicking::panic_bounds_check
             at libcore/panicking.rs:60
  10: <clippy_lints::map_clone::Pass as rustc::lint::LateLintPass<'a, 'tcx>>::check_expr
             at clippy_lints/src/map_clone.rs:39
  11: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
  12: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_block
  13: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
  14: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_body
  15: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_nested_body
  16: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_fn
  17: rustc::hir::intravisit::walk_item
  18: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_item
  19: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_mod
  20: rustc::hir::intravisit::walk_item
  21: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_item
  22: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_mod
  23: rustc::hir::intravisit::walk_item
  24: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_item
  25: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_mod
  26: rustc::hir::intravisit::walk_item
  27: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_item
  28: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_mod
  29: rustc::hir::intravisit::walk_item
  30: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_item
  31: <rustc::lint::context::LateContext<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_mod
  32: rustc::hir::intravisit::walk_crate
  33: rustc::lint::context::check_crate
  34: rustc::util::common::time
  35: rustc::ty::context::tls::enter_context
  36: <std::thread::local::LocalKey<T>>::with
  37: rustc::ty::context::TyCtxt::create_and_enter
  38: rustc_driver::driver::compile_input
  39: rustc_driver::run_compiler_with_pool
  40: <scoped_tls::ScopedKey<T>>::set
  41: syntax::with_globals
  42: rustc_driver::run_compiler
  43: clippy_driver::main
             at src/driver.rs:136
  44: std::rt::lang_start::{{closure}}
             at /checkout/src/libstd/rt.rs:74
  45: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  46: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  47: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  48: std::rt::lang_start
             at /checkout/src/libstd/rt.rs:74
  49: main
  50: __libc_start_main
  51: _start
query stack during panic:
end of query stack
error: Could not compile `distinst`.

[mati865]

No so minimal repro with BoolExt borrowed from distinst:

pub trait BoolExt {
    fn map<T, F: Fn() -> T>(&self, action: F) -> Option<T>;
}

impl BoolExt for bool {
    fn map<T, F: Fn() -> T>(&self, action: F) -> Option<T> {
        if *self {
            Some(action())
        } else {
            None
        }
    }
}

fn ice() {
    let a = true;
    a.map(|| false);
}

a.map(|| false) triggers panic here:
https://github.com/rust-lang-nursery/rust-clippy/blob/bb2f6a5011f938023d0ead64a746e0fa82f91ee6/clippy_lints/src/map_clone.rs#L39

Note body.arguments is empty at this point:

Body {
    arguments: [],
    value: expr(59: false),
    is_generator: false
}