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fix: Make native modules built with Neon work in Bun #914

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merged 1 commit into from
Jul 8, 2022
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@kjvalencik kjvalencik commented Jul 7, 2022

bun is a new JavaScript runtime designed to be Node.js compatible--including Node-API. However, it currently ships with an incomplete set of Node-APIs.

The following changes symbol loading to print a warning to stderr if a symbol is missing instead of panicking. This should be no change on Node because symbols are guaranteed to exist if the Node-API version number matches. On bun, this converts a panic on load to a panic when attempting to use the API.

With these changes, simple Neon modules work with bun. However, because of Neon's heavily reliance on napi_get_instance_data, many more powerful features will not work until this API is implemented in bun.

@kjvalencik kjvalencik marked this pull request as draft July 7, 2022 21:39
@kjvalencik kjvalencik marked this pull request as ready for review July 8, 2022 14:41
@kjvalencik kjvalencik force-pushed the kv/bun branch 2 times, most recently from 553de18 to b60393d Compare July 8, 2022 14:58
expected_napi_version,
actual_napi_version,
);

let print_warn = |err| eprintln!("WARN: {}", err);
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Sample output:

WARN: bun: undefined symbol: napi_get_value_external
WARN: bun: undefined symbol: napi_close_escapable_handle_scope
WARN: bun: undefined symbol: napi_open_escapable_handle_scope
WARN: bun: undefined symbol: napi_create_external
WARN: bun: undefined symbol: napi_escape_handle
WARN: bun: undefined symbol: napi_set_instance_data
WARN: bun: undefined symbol: napi_get_instance_data

@@ -118,7 +118,7 @@ macro_rules! generate {

#[inline(never)]
fn panic_load<T>() -> T {
panic!("Must load N-API bindings")
panic!("Node-API symbol has not been loaded")
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Currently this panic stack looks like:

thread '<unnamed>' panicked at 'Node-API symbol has not been loaded', crates/neon/src/sys/bindings/functions.rs:307:5
stack backtrace:
   0: std::panicking::begin_panic
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b/library/std/src/panicking.rs:525:12
   1: neon::sys::bindings::functions::napi6::panic_load
             at /work/crates/neon/src/sys/bindings/mod.rs:121:13
   2: neon::sys::bindings::functions::napi6::NAPI::get_instance_data

The panic message itself doesn't explain what symbol is missing; instead it requires the backtrace to determine. This is by design because it's never expected to happen on Node and only having a single panic method for the defaults reduces binary bloat.

Do you think it's worth the cost to binary sizes (a bunch of unique functions that should never be executed) to have more clear error messages in bun? I personally feel that the backtrace is sufficient since eventually all symbols should be implemented.

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@dherman dherman left a comment

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Looks good! I made one README suggestion.

@kjvalencik kjvalencik merged commit fadda14 into main Jul 8, 2022
@kjvalencik kjvalencik deleted the kv/bun branch July 8, 2022 17:33
@kjvalencik kjvalencik mentioned this pull request Jul 9, 2022
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2 participants