107 lines
3.0 KiB
Rust
107 lines
3.0 KiB
Rust
use proc_macro::TokenStream;
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use quote::quote;
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use syn::{Data, DeriveInput, Fields, parse_macro_input};
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/// Derive macro for generating a `validate` method for a Theme struct.
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/// The `validate` method ensures that all values with the `validate` attribute are not `None`.
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/// Otherwise, an error message it output to both the log file and stdout and the program exits.
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///
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/// # Example
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///
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/// Valid themes pass through the program transitively without any messages being output.
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///
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/// ```
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/// use validate_theme_derive::ValidateTheme;
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///
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/// #[derive(ValidateTheme, Default)]
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/// struct Theme {
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/// pub name: String,
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/// #[validate]
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/// pub good: Option<Style>,
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/// #[validate]
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/// pub bad: Option<Style>,
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/// pub ugly: Option<Style>,
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/// }
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///
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/// struct Style {
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/// color: String,
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/// }
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///
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/// let theme = Theme {
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/// good: Some(Style { color: "Green".to_owned() }),
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/// bad: Some(Style { color: "Red".to_owned() }),
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/// ..Theme::default()
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/// };
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///
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/// // Since only `good` and `bad` have the `validate` attribute, the `validate` method will only check those fields.
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/// theme.validate();
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/// // Since both `good` and `bad` have values, the program will not exit and no message is output.
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/// ```
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///
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/// Invalid themes will output an error message to both the log file and stdout and the program will exit.
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///
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/// ```should_panic
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/// use validate_theme_derive::ValidateTheme;
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///
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/// #[derive(ValidateTheme, Default)]
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/// struct Theme {
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/// pub name: String,
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/// #[validate]
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/// pub good: Option<Style>,
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/// #[validate]
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/// pub bad: Option<Style>,
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/// pub ugly: Option<Style>,
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/// }
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///
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/// struct Style {
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/// color: String,
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/// }
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///
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/// let theme = Theme {
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/// bad: Some(Style { color: "Red".to_owned() }),
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/// ..Theme::default()
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/// };
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///
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/// // Since `good` has the `validate` attribute and since `good` is `None`, the `validate` method will output an error message and exit the program.
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/// theme.validate();
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/// ```
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#[proc_macro_derive(ValidateTheme, attributes(validate))]
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pub fn derive_validate_theme(input: TokenStream) -> TokenStream {
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let input = parse_macro_input!(input as DeriveInput);
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let struct_name = &input.ident;
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let mut validation_checks = Vec::new();
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if let Data::Struct(data_struct) = &input.data {
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if let Fields::Named(fields) = &data_struct.fields {
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for field in &fields.named {
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let field_name = &field.ident;
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let has_validate_attr = field
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.attrs
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.iter()
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.any(|attr| attr.path().is_ident("validate"));
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if has_validate_attr {
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validation_checks.push(quote! {
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if self.#field_name.is_none() {
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log::error!("{} is missing a color value.", stringify!(#field_name));
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eprintln!("{} is missing a color value.", stringify!(#field_name));
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std::process::exit(1);
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}
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})
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}
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}
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}
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}
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quote! {
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impl #struct_name {
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pub fn validate(&self) {
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#(#validation_checks)*
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}
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}
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}
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.into()
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}
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