wasm-bindgen/guide/src/contributing/web-sys/logging.md

# Logging

The `wasm_bindgen_webidl` crate (used by `web-sys`'s `build.rs`) uses
[`env_logger`][env_logger] for logging, which can be enabled by setting the
`RUST_LOG=wasm_bindgen_webidl` environment variable while building the `web-sys`
crate.

Make sure to enable "very verbose" output during `cargo build` to see these logs
within `web-sys`'s build script output.

```sh
cd crates/web-sys
RUST_LOG=wasm_bindgen_webidl cargo build -vv
```

If `wasm_bindgen_webidl` encounters WebIDL constructs that it doesn't know how
to translate into `wasm-bindgen` AST items, it will emit warn-level logs.

```
WARN 2018-07-06T18:21:49Z: wasm_bindgen_webidl: Unsupported WebIDL interface: ...
```

[env_logger]: https://crates.io/crates/env_logger
Create the `web-sys` crate mechanically from WebIDL (#409) * Create a new `web-sys` crate This will eventually contain all the WebIDL-generated bindings to Web APIs. * ci: Test the new `web-sys` crate in CI * web-sys: Add a small README * web-sys: Vendor all the WebIDL files from mozilla-central * backend: Add a pass to remove AST items that use undefined imports This is necessary for the WebIDL frontend, which can't translate many WebIDL constructs into equivalent wasm-bindgen AST things yet. It lets us make incremental progress: we can generate bindings to methods we can support right now even though there might be methods on the same interface that we can't support yet. * webidl: Add a bunch of missing semicolons * webidl: Make parsing private It was only `pub` so that we could test it, but we ended up moving towards integration tests rather than unit tests that assert particular ASTs are parsed from WebIDL files. * webidl: Remove uses of undefined import types * test-project-builder: Build projects in "very verbose" mode This helps for debugging failing WebIDL-related tests. * test-project-builder: Add more profiling timers * test-project-builder: Detect when webpack-dev-server fails Instead of going into an infinite loop, detect when webpack-dev-server fails to start up and early exit the test. * webidl: Specify version for dev-dependency on wasm-bindgen-backend Instead of only a relative path. * guide: Add section about contributing to `web-sys` * WIP enable Event.webidl Still need to fix and finish the test. * Update expected webidl output * Start out a test's status as incomplete That way if we don't fill it in the error message doesn't look quite so bizarre * Fix onerror function in headless mode Otherwise we don't see any output! * Fix package.json/node_modules handling in project generation Make sure these are looked up in the git project root rather than the crate root * Avoid logging body text This was meant for debugging and is otherwise pretty noisy * Fix a relative path * More expected test fixes * Fix a typo * test-project-builder: Allow asynchronous tests * webidl: Convert [Unforgeable] attributes into `#[wasm_bindgen(structural)]` Fixes #432 * test-project-builder: Print generated WebIDL bindings for debugging purposes Helps debug bad WebIDL bindings generation inside tests. * When we can't find a descriptor, say which one can't be found This helps when debugging things that need to become structural. * web-sys: Test bindings for Event * ci: Use `--manifest-path dir` instead of `cd dir && ...` * web-sys: Just move .webidl files isntead of symlinking to enable them * tests: Polyfill Array.prototype.values for older browsers in CI * test-project-builder: Don't panic on poisoned headless test mutex We only use it to serialize headless tests so that we don't try to bind the port concurrently. Its OK to run another headless test if an earlier one panicked. * JsValue: Add {is,as}_{object,function} methods Allows dynamically casting values to `js::Object` and `js::Function`. * tidy: Fix whitespace and missing semicolons * Allow for dynamic feature detection of methods If we create bindings to a method that doesn't exist in this implementation, then it shouldn't fail until if/when we actually try and invoke that missing method. * tests: Do feature detection in Array.prototype.values test * Add JsValue::{is_string, as_js_string} methods And document all the cast/convert/check methods for js value. * eslint: allow backtick string literals * Only generate a fallback import function for non-structural imports 2018-07-09 16:35:25 -07:00			`# Logging`

			The `wasm_bindgen_webidl` crate (used by `web-sys`'s `build.rs`) uses
			[`env_logger`][env_logger] for logging, which can be enabled by setting the
			`RUST_LOG=wasm_bindgen_webidl` environment variable while building the `web-sys`
			`crate.`

			Make sure to enable "very verbose" output during `cargo build` to see these logs
			within `web-sys`'s build script output.

			```sh
			`cd crates/web-sys`
			`RUST_LOG=wasm_bindgen_webidl cargo build -vv`
			```

			If `wasm_bindgen_webidl` encounters WebIDL constructs that it doesn't know how
			to translate into `wasm-bindgen` AST items, it will emit warn-level logs.

			```
			`WARN 2018-07-06T18:21:49Z: wasm_bindgen_webidl: Unsupported WebIDL interface: ...`
			```

			`[env_logger]: https://crates.io/crates/env_logger`