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Updated contribution documentation (boa-dev#297)
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| # Debugging | ||
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| There are multiple ways to debug what Boa is doing. Or maybe you just want to know how it works under the hood. Or even test some JavaScript. | ||
| There are multiple ways to debug what Boa is doing. Or maybe you just want to | ||
| know how it works under the hood. Or even test some JavaScript. | ||
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| One way to do so is to create a file in the root of the repository. For example `test.js`. Then execute `cargo run -- test.js` to run the file with boa. | ||
| One way to do so is to create a file in the root of the repository. For example | ||
| `test.js`. Then execute `cargo run -- test.js` to run the file with boa. You can | ||
| compile a list of JavaScript files by running `cargo run -- file1.js file2.js` | ||
| and so on. | ||
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| You can also run boa interactively by simply calling `cargo run` without any arguments to start a shell to execute JS. | ||
| You can also run boa interactively by simply calling `cargo run` without any | ||
| arguments to start a shell to execute JS. | ||
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| These are added in order of how the code is read: | ||
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| ## Tokens | ||
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| The first thing boa will do is generate tokens from source code. | ||
| If the token generation is wrong the rest of the operation will be wrong, this is usually a good starting place. | ||
| The first thing boa will do is generate tokens from source code. If the token | ||
| generation is wrong the rest of the operation will be wrong, this is usually | ||
| a good starting place. | ||
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| To print the tokens to stdout, you can use the `boa_cli` command-line flag `--dump-tokens`, which can optionally take a format type. Supports these formats: `Debug`, `Json`, `JsonPretty`. By default it is the `Debug` format. | ||
| To print the tokens to stdout, you can use the `boa_cli` command-line flag | ||
| `--dump-tokens` or `-t`, which can optionally take a format type. Supports | ||
| these formats: `Debug`, `Json`, `JsonPretty`. By default it is the `Debug` | ||
| format. | ||
| ```bash | ||
| cargo run -- test.js --dump-tokens # token dump format is Debug by default. | ||
| ``` | ||
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| or with interactive mode (REPL): | ||
| ```bash | ||
| cargo run -- --dump-tokens # token dump format is Debug by default. | ||
| ``` | ||
| Seeing the order of tokens can be a big help to understanding what the parser | ||
| is working with. | ||
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| Or you can do it manually by navigating to `parser_expr` in [lib.rs](../boa/src/lib.rs#L25) and add `dbg!(&tokens);` just below tokens to see the array of token output. You code should look like this: | ||
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| ```rust | ||
| let mut lexer = Lexer::new(src); | ||
| lexer.lex().expect("lexing failed"); | ||
| let tokens = lexer.tokens; | ||
| dbg!(&tokens); | ||
| ... | ||
| ``` | ||
| Seeing the order of tokens can be a big help to understanding what the parser is working with. | ||
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| **Note:** flags `--dump-tokens` and `--dump-ast` are mutually exclusive. When using the flag `--dump-tokens`, the code will not be executed. | ||
| **Note:** flags `--dump-tokens` and `--dump-ast` are mutually exclusive. When | ||
| using the flag `--dump-tokens`, the code will not be executed. | ||
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| ## Expressions | ||
| ## AST nodes | ||
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| Assuming the tokens looks fine, the next step is to see the AST. | ||
| You can use the `boa_cli` command-line flag `--dump-ast`, which can optionally take a format type. Supports these formats: `Debug`, `Json`, `JsonPretty`. By default it is the `Debug` format. | ||
| Assuming the tokens looks fine, the next step is to see the AST. You can use | ||
| the `boa_cli` command-line flag `--dump-ast`, which can optionally take a | ||
| format type. Supports these formats: `Debug`, `Json`, `JsonPretty`. By default | ||
| it is the `Debug` format. | ||
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| Dumping the AST of a file: | ||
| ```bash | ||
| cargo run -- test.js --dump-ast # AST dump format is Debug by default. | ||
| ``` | ||
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| or with interactive mode (REPL): | ||
| ```bash | ||
| cargo run -- --dump-ast # AST dump format is Debug by default. | ||
| ``` | ||
| Or manually, you can output the expressions in [forward](../boa/src/lib.rs#L36), add `dbg!(&expr);` | ||
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| These methods will print out the entire parse tree. | ||
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| **Note:** flags `--dump-tokens` and `--dump-ast` are mutually exclusive. When using the flag `--dump-ast`, the code will not be executed. | ||
| **Note:** flags `--dump-tokens` and `--dump-ast` are mutually exclusive. When | ||
| using the flag `--dump-ast`, the code will not be executed. | ||
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| ## Compiler panics | ||
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| In the case of a compiler panic, to get a full backtrace you will need to set | ||
| the environment variable `RUST_BACKTRACE=1`. | ||
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| ## Execution | ||
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| Once the tree has been generated [exec](../boa/src/lib.rs#L67) will begin to run through each expression. If the tokens and tree looks fine, you can start looking here. | ||
| I usually just add `dbg!()` in the relevent places to see what the output is at the time. | ||
| Once the tree has been generated [exec](../boa/src/lib.rs#L92) will begin to | ||
| run through each node. If the tokens and tree looks fine, you can start looking | ||
| here. We usually just add `dbg!()` in the relevent places to see what the | ||
| output is at the time. | ||
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| ## Debugger | ||
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| ### VS Code Debugger | ||
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| The quickest way to get debugging is to re-open the workspace in the container (using the Dockerfile provided). This is using the [Remote Containers plugin](https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.remote-containers). Once inside make sure you have the CodeLLDB extension installed and add breakpoints. | ||
| The quickest way to get debugging is to use the CodeLLDB plugin and add breakpoints. You can get | ||
| more information [here][blog_debugging]. | ||
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| ### LLDB Manual debugging | ||
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| You can also use rust-lldb. The `Dockerfile` already has this enabled, you | ||
| should be able to use that environment to run your code. | ||
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| ### LLDB Manually | ||
| ``` | ||
| rust-lldb ./target/debug/boa [arguments] | ||
| ``` | ||
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| You can also use rust-lldb. | ||
| The `Dockerfile` already has this enabled, you should be able to use that environment to run your code. | ||
| `rust-lldb ./target/debug/boa [arguments]` | ||
| [remote_containers]: https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.remote-containers | ||
| [blog_debugging]: https://jason-williams.co.uk/debugging-rust-in-vscode |