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use std::fmt::{Debug, Display}; use liquid_error::Result; use liquid_interpreter::{Context, Expression}; use liquid_value::Value; /// A structure that holds the information of a single parameter in a filter. /// This includes its name, description and whether it is optional or required. /// /// This is the return type in some `FilterReflection` functions. pub struct ParameterReflection { pub name: &'static str, pub description: &'static str, pub is_optional: bool, } /// A trait that holds the information of the parameters of a filter. /// /// All structs that implement `FilterParameters` must implement this. /// This is actually automatically implemented with `#[derive(FilterParameters)]`. /// /// This trait allows `FilterReflection` macro to extract the parameters information /// from a given `FilterParameters` structure. pub trait FilterParametersReflection { fn positional_parameters() -> &'static [ParameterReflection]; fn keyword_parameters() -> &'static [ParameterReflection]; } /// A trait that holds the information of a filter about itself, such as /// its name, description and parameters. /// /// All structs that implement `ParseFilter` must implement this. /// /// # Deriving /// /// This trait may be derived with `liquid-derive`'s `#[derive(FilterReflection)]`. However, /// it is necessary to use the `#[filter(...)]` helper attribute. See documentation on /// `liquid-derive` for more information. pub trait FilterReflection { fn name(&self) -> &'static str; fn description(&self) -> &'static str; fn positional_parameters(&self) -> &'static [ParameterReflection]; fn keyword_parameters(&self) -> &'static [ParameterReflection]; } /// A trait that declares and holds the parameters of a filter. /// /// Provides `from_args`, to construct itself from `FilterArguments` (parses the arguments) /// and `evaluate`, to construct its evaluated counterpart (evaluates the arguments). /// /// # Deriving /// /// The whole point of this structure is to facilitate the process of deriving a filter. /// Thus, this trait and all traits it requires may be derived with `#[derive(Debug, FilterParameters)]`. /// /// See documentation for `FilterParameters` macro on `liquid-derive` for more information. pub trait FilterParameters<'a>: Sized + FilterParametersReflection + Debug + Display { type EvaluatedFilterParameters; fn from_args(args: FilterArguments) -> Result<Self>; fn evaluate(&'a self, context: &'a Context) -> Result<Self::EvaluatedFilterParameters>; } /// Structure that holds the unparsed arguments of a filter, both positional and keyword. pub struct FilterArguments<'a> { pub positional: Box<Iterator<Item = Expression>>, pub keyword: Box<Iterator<Item = (&'a str, Expression)> + 'a>, } /// A trait that holds a filter, ready to evaluate. /// /// # Deriving /// /// You cannot derive `Filter`, as it would go against the very point of creating your own filter. /// You can, however, derive some other traits that are necessary in order to implement it. /// /// In order to implement this trait, the struct must also implement `Debug` and `Display`, as well /// as either `Default` or `From<T>` (where T is the FilterParameters struct), respectively, in a /// filter without or with parameters. /// /// For `Debug` and `Default`, one may use rust's `#[derive(Debug)]` and `#[derive(Default)]` macros. /// For `Display` and `From<T>`, one may use `liquid-derive`'s `#[derive(Display_filter)]` and /// `#[derive(FromFilterParameters)]`. /// /// Note, however, that you may need helper attributes like `#[name = "..."]` and `#[parameters]` for /// using liquid-derive`'s macros. See documentation on `liquid-derive` for more information. /// /// # Examples /// /// Filter for filter with no arguments: /// ```ignore /// #[derive(Debug, Default, Display_filter)] /// #[name = "abs"] // The name of the filter, for `Display_filter`. /// struct AbsFilter; // There are no parameters, so implements `Default`. /// /// impl Filter for AbsFilter { /// fn evaluate(&self, input: &Value, _context: &Context) -> Result<Value> { /// // Implementation of the filter here /// } /// } /// ``` /// /// Filter for filter with arguments: /// ```ignore /// #[derive(Debug, FromFilterParameters, Display_filter)] /// #[name = "at_least"] // The name of the filter for derives /// struct AtLeastFilter { // There are parameters, so derives `FromFilterParameters`. /// #[parameters] // Mark the FilterParameters struct for derives /// args: AtLeastArgs, // A struct that implements `FilterParameters` /// } /// /// impl Filter for AtLeastFilter { /// fn evaluate(&self, input: &Value, context: &Context) -> Result<Value> { /// // Evaluate the `FilterParameters` /// let args = self.args.evaluate(context)?; /// /// // Implementation of the filter here /// } /// } /// ``` /// /// Filter for a configurable filter: /// ```ignore /// #[derive(Debug, Display_filter)] /// #[name = "example"] // The name of the filter for `Display` /// // Because construction happens manually (without derive) in `FilterParser` /// // no need to derive neither `Default` nor `FromFilterParameters`. /// struct ExampleFilter { /// #[parameters] // Mark the FilterParameters struct for `Display` /// args: ExampleArgs, // A struct that implements `FilterParameters` /// state: i32, // See `ParseFilter` example for context /// } /// /// impl Filter for AtLeastFilter { /// fn evaluate(&self, input: &Value, context: &Context) -> Result<Value> { /// // Evaluate the `FilterParameters` /// let args = self.args.evaluate(context)?; /// /// // Implementation of the filter here /// } /// } /// ``` pub trait Filter: Send + Sync + Debug + Display { // This will evaluate the expressions and evaluate the filter. fn evaluate(&self, input: &Value, context: &Context) -> Result<Value>; } /// A trait to register a new filter in the `liquid::Parser`. /// /// To implement this trait, the structure must also implement `FilterReflection`, thus giving /// meta information about the filter (namely it's name). /// /// Every time a filter with that name is encountered, it is parsed with the `ParseFilter::parse` /// method, yielding a new `Filter`. /// /// # Deriving /// /// In order to implement this trait, the struct must also implement `FilterReflection` and /// `Clone`. /// /// `Clone` may be derived with rust's `#[derive(Clone)]`. `FilterReflection` may be derived /// with `liquid-derive`'s `#[derive(FilterReflection)]`. ParseFilter may be derived with /// `#[derive(FilterReflection)]`. /// /// In order to use `liquid-derive`'s macros, however, it is necessary to use the `#[filter(...)]` /// helper attribute. See documentation on `liquid-derive` for more information. /// /// # Examples /// /// ParseFilter for filter with no arguments: /// ```ignore /// #[derive(Clone, ParseFilter, FilterReflection)] /// #[filter( /// name = "abs", /// description = "Returns the absolute value of a number.", /// parsed(AbsFilter) // A struct that implements `Filter` (must implement `Default`) /// )] /// pub struct Abs; /// ``` /// /// ParseFilter for filter with arguments: /// ```ignore /// #[derive(Clone, ParseFilter, FilterReflection)] /// #[filter( /// name = "slice", /// description = "Takes a slice of a given string or array.", /// parameters(SliceArgs), // A struct that implements `FilterParameters` /// parsed(SliceFilter) // A struct that implements `Filter` (must implement `From<SliceArgs>`) /// )] /// pub struct Slice; /// ``` /// /// ParseFilter for a configurable filter: /// ```ignore /// #[derive(Clone, FilterReflection)] /// #[filter( /// name = "example", /// description = "This filter exists for example purposes.", /// parameters(ExampleArgs) // A struct that implements `FilterParameters` /// )] /// pub struct ExampleParser { /// // You can add as many fields as you find necessary to configure the filter /// // before registering it. /// pub mode: i32, /// } /// /// // For configurable filters, there is no default implementation of `ParseFilter` /// impl ParseFilter for ExampleParser { /// fn parse(&self, arguments: FilterArguments) -> Result<Box<Filter>> { /// // Create the `FilterParameters` struct from the given `arguments` /// let args = ExampleArgs::from_args(arguments)?; /// // Use the configuration state of the `ParseFilter` /// let state = self.state; /// /// // Create the `Filter` struct and return it, passing the information /// // about the arguments and the configuration of the `ParseFilter`. /// Ok(Box::new(ExampleFilter { args, state })) /// } /// } /// ``` pub trait ParseFilter: Send + Sync + ParseFilterClone + FilterReflection { /// Filter `input` based on `arguments`. fn parse(&self, arguments: FilterArguments) -> Result<Box<Filter>>; } /// Support cloning of `Box<ParseFilter>`. pub trait ParseFilterClone { /// Cloning of `dyn ParseFilter`. fn clone_box(&self) -> Box<ParseFilter>; } impl<T> ParseFilterClone for T where T: 'static + ParseFilter + Clone, { fn clone_box(&self) -> Box<ParseFilter> { Box::new(self.clone()) } } impl Clone for Box<ParseFilter> { fn clone(&self) -> Box<ParseFilter> { self.clone_box() } } impl<T> From<T> for Box<ParseFilter> where T: 'static + ParseFilter, { fn from(filter: T) -> Self { Box::new(filter) } }