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49 lines
2.0 KiB
49 lines
2.0 KiB
5 years ago
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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.
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The first thing i usually do is add some JS [here](../tests/js/test.js).
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This file will be read if no arguments are provided. Then boa will begin to parse and execute that 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.
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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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Navigate to `parser_expr` in [lib.rs](../src/lib/lib.rs#L48) 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
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let mut lexer = Lexer::new(src);
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lexer.lex().expect("lexing failed");
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let tokens = lexer.tokens;
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dbg!(&tokens);
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...
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```
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Seeing the order of tokens can be a big help to understanding what the parser is working with.
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## Expressions
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Assuming the tokens looks fine, the next step is to see the AST.
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You can output the expressions in [forward](../src/lib/lib.rs#L57), add `dbg!(&expr);`
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This will print out the entire parse tree.
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## Execution
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Once the tree has been generated [exec](../src/lib/exec.rs#L66) will begin to run through each expression. If the tokens and tree looks fine, you can start looking here.
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I 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.
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### LLDB Manually
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You can also use rust-lldb.
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The `Dockerfile` already has this enabled, you should be able to use that environment to run your code.
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`rust-lldb ./target/debug/boa [arguments]`
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