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//! Helper trait and types for the default set of helpers. //! //! The [Helper Trait](self::Helper) should be implemented //! for custom helpers which can then be added to a registry. //! //! Helper `call()` functions accept three arguments: //! //! * [rc](crate::render::Render) The active renderer. //! * [ctx](crate::render::context::Context) Helper arguments and hash parameters. //! * [template](crate::parser::ast::Node) Inner template when called as a block. //! //! The renderer can be used to render inner templates when a helper //! is called as a block and provides functions for writing to the output destination. //! //! The context is used to access the arguments and hash parameters and may also //! be used for type assertions. //! //! When a helper is called as a block the optional template node will be `Some`. //! Raw helpers can access the inner text using [text()](crate::render::context::Context#method.text). //! //! To determine how a helper was invoked requires checking for an inner template //! or raw text; if neither is available it is a statement: //! //! ```ignore //! if let Some(node) = template { //! // Helper was invoked as a block `{{#helper}}...{{/helper}}` //! } else if let Some(text) = ctx.text() { //! // Helper was invoked as a raw block `{{{{helper}}}}...{{{{/helper}}}}` //! } else { //! // Helper was invoked as a statement `{{helper}}` //! } //! ``` //! //! ## Type Assertions //! //! Type assertions let us verify the type of helper arguments and hash parameters before we //! use them. //! //! The [arity()](crate::render::context::Context#method.arity) method is used to //! assert on argument length. //! //! Use [try_get()](crate::render::context::Context#method.try_get) to get an argument and verify //! it is an expected type. //! //! Use [try_param()](crate::render::context::Context#method.try_param) to get a hash parameter //! and verify it is an expected type. //! //! ## Return Values //! //! The signature for helper return values is [HelperValue](HelperValue) which requires //! that the `call()` function returns an optional [Value](serde_json::Value). //! //! A return value is useful when a helper is invoked as a statement; when invoked as //! a block return `Ok(None)`. //! //! If a statement helper is used for side-effects (such as the [Log](log::Log) helper) then //! return `Ok(None)`. //! //! ## Local Helpers //! //! Local helpers are defined on [rc](crate::render::Render) using [register_local_helper()](crate::render::Render#method.register_local_helper) and live for the lifetime of the parent helper call. //! //! They must implement the [LocalHelper Trait](LocalHelper) which has an additional bounds on //! `Clone`. //! //! ## Render //! //! To render an inner template when a helper is called as a block use //! [template()](crate::render::Render#method.template) which will respect the current whitespace //! trim hints: //! //! ```ignore //! if let Some(node) = template { //! rc.template(node)?; //! } //! ``` //! //! To [buffer()](crate::render::Render#method.template) the content of an inner template into a string: //! //! ```ignore //! if let Some(node) = template { //! let content = rc.buffer(node)?; //! } //! ``` //! use dyn_clone::DynClone; use serde_json::Value; use std::collections::HashMap; use crate::{ error::HelperError, parser::ast::Node, render::{Context, Render}, }; /// Result type returned when invoking helpers. pub type HelperResult<T> = std::result::Result<T, HelperError>; /// Result type that helper implementations should return. pub type HelperValue = HelperResult<Option<Value>>; /// Trait for helpers. pub trait Helper: Send + Sync { /// Function that is called when this helper is resolved /// by the renderer for a statement or block. /// /// The `rc` argument is the render context that can be used /// to render inner templates and write to the destination output. /// /// The `ctx` argument provides access to the helper arguments and /// hash parameters. It also provides support for type assertions and /// some convenience functions for working with the [Value](serde_json::Value) type. /// /// The `template` argument holds the inner template when the helper /// is invoked as a block. /// /// For raw block helpers use the [text()](crate::render::Context#method.text) /// function on `ctx` to access the underlying string slice. fn call<'render, 'call>( &self, rc: &mut Render<'render>, ctx: &Context<'call>, template: Option<&'render Node<'render>>, ) -> HelperValue; } /// Trait for local helpers which must implement `Clone`. /// /// To create a local helper implement `Helper`, derive `Clone` and /// add `LocalHelper` as a marker trait. /// /// ```ignore /// #[derive(Clone)] /// pub struct LocalExample; /// /// impl Helper for LocalExample { /// fn call<'render, 'call>( /// &self, /// _rc: &mut Render<'render>, /// _ctx: &Context<'call>, /// _template: Option<&'render Node<'render>>, /// ) -> HelperValue { Ok(None) } /// } /// impl LocalHelper for LocalExample {} /// ``` pub trait LocalHelper: Helper + DynClone {} dyn_clone::clone_trait_object!(LocalHelper); pub mod prelude; #[cfg(feature = "comparison-helper")] pub mod comparison; #[cfg(feature = "each-helper")] pub mod each; #[cfg(feature = "conditional-helper")] pub mod r#if; #[cfg(feature = "json-helper")] pub mod json; #[cfg(feature = "log-helper")] pub mod log; #[cfg(feature = "logical-helper")] pub mod logical; #[cfg(feature = "lookup-helper")] pub mod lookup; #[cfg(feature = "conditional-helper")] pub mod unless; #[cfg(feature = "with-helper")] pub mod with; /// Collection of helpers. #[derive(Default)] pub struct HelperRegistry<'reg> { helpers: HashMap<&'reg str, Box<dyn Helper + 'reg>>, } impl<'reg> HelperRegistry<'reg> { /// Create a collection of helpers. /// /// Helpers configured using the compiler feature flags are /// automatically added to this collection. /// /// If you need a helper collection without the builtin helpers /// use `Default::default()`. pub fn new() -> Self { let mut reg = Self { helpers: Default::default(), }; reg.builtins(); reg } fn builtins(&mut self) { #[cfg(feature = "conditional-helper")] self.insert("if", Box::new(r#if::If {})); #[cfg(feature = "conditional-helper")] self.insert("unless", Box::new(unless::Unless {})); #[cfg(feature = "comparison-helper")] self.insert("eq", Box::new(comparison::Equal {})); #[cfg(feature = "comparison-helper")] self.insert("ne", Box::new(comparison::NotEqual {})); #[cfg(feature = "comparison-helper")] self.insert("gt", Box::new(comparison::GreaterThan {})); #[cfg(feature = "comparison-helper")] self.insert("gte", Box::new(comparison::GreaterThanEqual {})); #[cfg(feature = "comparison-helper")] self.insert("lt", Box::new(comparison::LessThan {})); #[cfg(feature = "comparison-helper")] self.insert("lte", Box::new(comparison::LessThanEqual {})); #[cfg(feature = "log-helper")] self.insert("log", Box::new(log::Log {})); #[cfg(feature = "lookup-helper")] self.insert("lookup", Box::new(lookup::Lookup {})); #[cfg(feature = "logical-helper")] self.insert("and", Box::new(logical::And {})); #[cfg(feature = "logical-helper")] self.insert("or", Box::new(logical::Or {})); #[cfg(feature = "logical-helper")] self.insert("not", Box::new(logical::Not {})); #[cfg(feature = "with-helper")] self.insert("with", Box::new(with::With {})); #[cfg(feature = "each-helper")] self.insert("each", Box::new(each::Each {})); #[cfg(feature = "json-helper")] self.insert("json", Box::new(json::Json {})); } /// Insert a helper into this collection. pub fn insert(&mut self, name: &'reg str, helper: Box<dyn Helper + 'reg>) { self.helpers.insert(name, helper); } /// Remove a helper from this collection. pub fn remove(&mut self, name: &'reg str) { self.helpers.remove(name); } /// Get a helper from this collection. pub fn get(&self, name: &str) -> Option<&Box<dyn Helper + 'reg>> { self.helpers.get(name) } }