Add a new trait to ContextElement for Truthiness.

Before I was relying on Loopable to both determine truthiness and get a list of elements to loop over. This will no longer work since I need to only set $idx and $len when iterating over actual arrays, as opposed to all truthy values, so I've finally made truthiness explicit.

src/bin.rs

@@ -10,6 +10,7 @@ use renderer::DustRenderer;
 use renderer::Loopable;
 use renderer::RenderError;
 use renderer::Renderable;
+use renderer::Truthiness;
 use renderer::WalkError;
 use renderer::Walkable;
 use std::cmp::Ordering;
@@ -236,6 +237,19 @@ fn apply_filters(
 
 impl ContextElement for serde_json::Value {}
 
+impl Truthiness for serde_json::Value {
+    fn is_truthy(&self) -> bool {
+        match self {
+            serde_json::Value::Null => false,
+            serde_json::Value::Bool(boolean) => *boolean,
+            serde_json::Value::Number(_num) => true,
+            serde_json::Value::String(string_value) => !string_value.is_empty(),
+            serde_json::Value::Array(array_value) => !array_value.is_empty(),
+            serde_json::Value::Object(_obj) => true,
+        }
+    }
+}
+
 impl Renderable for serde_json::Value {
     fn render(&self, _filters: &Vec<Filter>) -> Result<String, RenderError> {
         let after_apply = if _filters.is_empty() {

src/renderer/context_element.rs

@@ -5,10 +5,20 @@ use std::any::Any;
 use std::{cmp::Ordering, fmt::Debug};
 
 pub trait ContextElement:
-    Debug + Walkable + Renderable + Loopable + CloneIntoBoxedContextElement + CompareContextElement
+    Debug
+    + Truthiness
+    + Walkable
+    + Renderable
+    + Loopable
+    + CloneIntoBoxedContextElement
+    + CompareContextElement
 {
 }
 
+pub trait Truthiness {
+    fn is_truthy(&self) -> bool;
+}
+
 pub trait Walkable {
     fn walk(&self, segment: &str) -> Result<&dyn ContextElement, WalkError>;
 }

src/renderer/iteration_context.rs

@@ -3,6 +3,7 @@ use crate::renderer::context_element::ContextElement;
 use crate::renderer::Loopable;
 use crate::renderer::RenderError;
 use crate::renderer::Renderable;
+use crate::renderer::Truthiness;
 use crate::renderer::WalkError;
 use crate::{parser::Filter, parser::OwnedLiteral, renderer::Walkable};
 
@@ -30,6 +31,15 @@ impl IterationContext {
 
 impl ContextElement for IterationContext {}
 
+impl Truthiness for IterationContext {
+    fn is_truthy(&self) -> bool {
+        // TODO: Would this even ever be called? Won't matter, but I'd
+        // like to know. Since it is injected 1 above the current
+        // context, we wouldn't be able to access it with `{.}`.
+        true
+    }
+}
+
 impl Renderable for IterationContext {
     fn render(&self, _filters: &Vec<Filter>) -> Result<String, RenderError> {
         // TODO: Would this even ever be called? Won't matter, but I'd

src/renderer/mod.rs

@@ -13,6 +13,7 @@ pub use context_element::CompareContextElement;
 pub use context_element::ContextElement;
 pub use context_element::Loopable;
 pub use context_element::Renderable;
+pub use context_element::Truthiness;
 pub use context_element::Walkable;
 pub use errors::CompileError;
 pub use errors::RenderError;

src/renderer/parameters_context.rs

@@ -6,6 +6,7 @@ use crate::renderer::walking::walk_path;
 use crate::renderer::Loopable;
 use crate::renderer::RenderError;
 use crate::renderer::Renderable;
+use crate::renderer::Truthiness;
 use crate::renderer::WalkError;
 use crate::renderer::Walkable;
 use std::{cmp::Ordering, collections::HashMap};
@@ -67,6 +68,15 @@ impl ParametersContext {
 
 impl ContextElement for ParametersContext {}
 
+impl Truthiness for ParametersContext {
+    fn is_truthy(&self) -> bool {
+        // TODO: Would this even ever be called? Won't matter, but I'd
+        // like to know. Since it is injected 1 above the current
+        // context, we wouldn't be able to access it with `{.}`.
+        true
+    }
+}
+
 impl Renderable for ParametersContext {
     fn render(&self, _filters: &Vec<Filter>) -> Result<String, RenderError> {
         // TODO: Would this even ever be called? Won't matter, but I'd
@@ -128,6 +138,15 @@ impl CompareContextElement for ParametersContext {
 
 impl ContextElement for OwnedLiteral {}
 
+impl Truthiness for OwnedLiteral {
+    fn is_truthy(&self) -> bool {
+        match self {
+            OwnedLiteral::LString(text) => !text.is_empty(),
+            OwnedLiteral::LPositiveInteger(num) => true,
+        }
+    }
+}
+
 impl Renderable for OwnedLiteral {
     fn render(&self, _filters: &Vec<Filter>) -> Result<String, RenderError> {
         match self {

src/renderer/renderer.rs

@@ -524,12 +524,19 @@ mod tests {
     use crate::parser::Filter;
     use crate::renderer::context_element::Loopable;
     use crate::renderer::context_element::Renderable;
+    use crate::renderer::context_element::Truthiness;
     use crate::renderer::context_element::Walkable;
     use crate::renderer::CompareContextElement;
     use std::cmp::Ordering;
 
     impl ContextElement for String {}
 
+    impl Truthiness for String {
+        fn is_truthy(&self) -> bool {
+            !self.is_empty()
+        }
+    }
+
     impl Renderable for String {
         fn render(&self, _filters: &Vec<Filter>) -> Result<String, RenderError> {
             Ok(self.clone())
@@ -569,6 +576,12 @@ mod tests {
     }
     impl ContextElement for u64 {}
 
+    impl Truthiness for u64 {
+        fn is_truthy(&self) -> bool {
+            true
+        }
+    }
+
     impl Renderable for u64 {
         fn render(&self, _filters: &Vec<Filter>) -> Result<String, RenderError> {
             Ok(self.to_string())
@@ -605,6 +618,12 @@ mod tests {
 
     impl<I: 'static + ContextElement + Clone> ContextElement for HashMap<String, I> {}
 
+    impl<I: ContextElement> Truthiness for HashMap<String, I> {
+        fn is_truthy(&self) -> bool {
+            true
+        }
+    }
+
     impl<I: ContextElement> Renderable for HashMap<String, I> {
         fn render(&self, _filters: &Vec<Filter>) -> Result<String, RenderError> {
             // TODO: handle the filters