Panic on wasm32-unknown-unknown without js feature

[jprochazk]

Suggested here: #296 (comment)

I quickly put together a hello-world trunk project, and called jiff::Zoned::new() in it, without the js feature enabled.

The resulting panic

panicked at /home/dev/jiff/src/now.rs:30:9:
getting the current time in wasm32-unknown-unknown is not possible, enable jiff's `js` feature if you are targeting a browser environment

Stack:

__wbg_get_imports/imports.wbg.__wbg_new_8a6f238a6ece86ea@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8.js:246:21
trunk_hello_world-a7f87d88668d9124.wasm.__wbg_new_8a6f238a6ece86ea externref shim@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2337]:0xace89
trunk_hello_world-a7f87d88668d9124.wasm.console_error_panic_hook::Error::new::hd7ee4fcdd982d38a@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[1604]:0xa261a
trunk_hello_world-a7f87d88668d9124.wasm.console_error_panic_hook::hook_impl::h8821c57ba8c469cf@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[384]:0x6b573
trunk_hello_world-a7f87d88668d9124.wasm.console_error_panic_hook::hook::ha79e4afb6a587815@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2127]:0xaae76
trunk_hello_world-a7f87d88668d9124.wasm.core::ops::function::Fn::call::hf0dffdd551dbc510@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[1836]:0xa6c59
trunk_hello_world-a7f87d88668d9124.wasm.std::panicking::rust_panic_with_hook::he163a328f096b027@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[861]:0x8ac32
trunk_hello_world-a7f87d88668d9124.wasm.std::panicking::begin_panic_handler::{{closure}}::h9b4576c502f796bb@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[1039]:0x92541
trunk_hello_world-a7f87d88668d9124.wasm.std::sys::backtrace::__rust_end_short_backtrace::h9dcf082627c76851@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2385]:0xad164
trunk_hello_world-a7f87d88668d9124.wasm.rust_begin_unwind@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2218]:0xac02e
trunk_hello_world-a7f87d88668d9124.wasm.core::panicking::panic_fmt::hf09e831ea9f1651a@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2219]:0xac05a
trunk_hello_world-a7f87d88668d9124.wasm.jiff::now::sys::system_time::h898a41a65599799d@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[1683]:0xa405a
trunk_hello_world-a7f87d88668d9124.wasm.jiff::zoned::Zoned::now::hc9862d1e6d3623ca@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[1068]:0x9364a
trunk_hello_world-a7f87d88668d9124.wasm.trunk_hello_world::main::h4c62d89c82d63174@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[232]:0x57da9
trunk_hello_world-a7f87d88668d9124.wasm.core::ops::function::FnOnce::call_once::h891fbf1087931a90@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2038]:0xa9c5a
trunk_hello_world-a7f87d88668d9124.wasm.std::sys::backtrace::__rust_begin_short_backtrace::h8f5930db5e671fb7@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2036]:0xa9bec
trunk_hello_world-a7f87d88668d9124.wasm.std::rt::lang_start::{{closure}}::hcdc519022ca63bd4@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[1292]:0x9aa9a
trunk_hello_world-a7f87d88668d9124.wasm.std::rt::lang_start_internal::hca8730f87f82319d@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[944]:0x8e7cf
trunk_hello_world-a7f87d88668d9124.wasm.std::rt::lang_start::he22437a03640fe91@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[1158]:0x9683b
trunk_hello_world-a7f87d88668d9124.wasm.main@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2302]:0xacb32
trunk_hello_world-a7f87d88668d9124.wasm.@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2362]:0xad048
trunk_hello_world-a7f87d88668d9124.wasm.@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8_bg.wasm:wasm-function[2391]:0xad19c
__wbg_finalize_init@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8.js:315:10
__wbg_init@http://127.0.0.1:8080/trunk-hello-world-39605882ec2e39d8.js:369:12


trunk-hello-world-39605882ec2e39d8.js:230:21

• Closes provide better panic message for Zoned::now on wasm32-unknown-unknown when js feature is not enabled #296 - the issue is about discoverability of the js feature, and this PR greatly improves that.

[BurntSushi]

Nice thank you! Just a few nits.

[jprochazk]

@BurntSushi Hi, could you please take another look at this?

[BurntSushi]

LGTM

[BurntSushi]

I pushed a tweak to the language here.