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<!-- if this PR closes one or more issues, you can automatically link the PR with them by using one of the [*linking keywords*](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword), e.g. - this PR should close #xxxx - fixes #xxxx you can also mention related issues, PRs or discussions! --> # Description <!-- Thank you for improving Nushell. Please, check our [contributing guide](../CONTRIBUTING.md) and talk to the core team before making major changes. Description of your pull request goes here. **Provide examples and/or screenshots** if your changes affect the user experience. --> Relative: #8248 After this pr, user can define const variable inside a module.  And user can export const variables, the following screenshot shows how it works (it follows https://github.com/nushell/nushell/issues/8248#issuecomment-1637442612):  ## About the change 1. To make module support const, we need to change `parse_module_block` to support `const` keyword. 2. To suport export `const`, we need to make module tracking variables, so we add `variables` attribute to `Module` 3. During eval, the const variable may not exists in `stack`, because we don't eval `const` when we define a module, so we need to find variables which are already registered in `engine_state` ## One more thing to note about the const value. Consider the following code ``` module foo { const b = 3; export def bar [] { $b } } use foo bar const b = 4; bar ``` The result will be 3 (which is defined in module) rather than 4. I think it's expected behavior. It's something like [dynamic binding](https://www.gnu.org/software/emacs/manual/html_node/elisp/Dynamic-Binding-Tips.html) vs [lexical binding](https://www.gnu.org/software/emacs/manual/html_node/elisp/Lexical-Binding.html) in lisp like language, and lexical binding should be right behavior which generates more predicable result, and it doesn't introduce really subtle bugs in nushell code. What if user want dynamic-binding?(For example: the example code returns `4`) There is no way to do this, user should consider passing the value as argument to custom command rather than const. ## TODO - [X] adding tests for the feature. - [X] support export const out of module to use. # User-Facing Changes <!-- List of all changes that impact the user experience here. This helps us keep track of breaking changes. --> # Tests + Formatting <!-- Don't forget to add tests that cover your changes. Make sure you've run and fixed any issues with these commands: - `cargo fmt --all -- --check` to check standard code formatting (`cargo fmt --all` applies these changes) - `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect -A clippy::result_large_err` to check that you're using the standard code style - `cargo test --workspace` to check that all tests pass - `cargo run -- -c "use std testing; testing run-tests --path crates/nu-std"` to run the tests for the standard library > **Note** > from `nushell` you can also use the `toolkit` as follows > ```bash > use toolkit.nu # or use an `env_change` hook to activate it automatically > toolkit check pr > ``` --> # After Submitting <!-- If your PR had any user-facing changes, update [the documentation](https://github.com/nushell/nushell.github.io) after the PR is merged, if necessary. This will help us keep the docs up to date. --> |
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nu-protocol
The nu-protocol crate holds the definitions of structs/traits that are used throughout Nushell. This gives us one way to expose them to many other crates, as well as make these definitions available to each other, without causing mutually recursive dependencies.