Add support for template-accessible methods and include leftpad and urlencode

Cargo.lock

@@ -782,6 +782,7 @@ dependencies = [
  "html-escape",
  "insta",
  "itertools",
+ "percent-encoding",
  "pollster",
  "thiserror",
  "tracing",

hornbeam_interpreter/Cargo.toml

@@ -25,6 +25,7 @@ itertools = "0.10.5"
 pollster = "0.3.0"
 
 tracing = "0.1.37"
+percent-encoding = "2.2.0"
 
 [features]
 default = ["fluent"]

hornbeam_interpreter/src/engine.rs

@@ -1,3 +1,4 @@
+use crate::functions::TemplateAccessibleMethod;
 use crate::interface::{LocalisationSystem, OutputSystem};
 use crate::InterpreterError;
 use async_recursion::async_recursion;
@@ -32,6 +33,7 @@ pub(crate) struct Interpreter<'a, O, LS> {
     pub(crate) localisation: Arc<LS>,
     pub(crate) locale: String,
     pub(crate) scopes: Vec<Scope<'a>>,
+    pub(crate) methods: &'a BTreeMap<String, TemplateAccessibleMethod>,
 }
 
 #[derive(Debug)]
@@ -727,8 +729,34 @@ impl<'a, O: OutputSystem + Send, LS: LocalisationSystem + Sync + Send> Interpret
                     }),
                 }
             }
-            Expression::MethodCall { .. } => {
+            Expression::MethodCall {
-                unimplemented!()
+                obj,
+                ident,
+                args,
+                loc,
+            } => {
+                let Some(method) = self.methods.get(ident.as_str()) else {
+                    return Err(InterpreterError::TypeError {
+                        context: format!("method call to {ident:?}"),
+                        conflict: format!("No method by that name!"),
+                        location: loc.clone(),
+                    });
+                };
+
+                let obj_value = self.evaluate_expression(scope_idx, obj, loc)?;
+                let mut arg_values: Vec<Value> = Vec::with_capacity(args.len());
+                for arg in args {
+                    arg_values.push(self.evaluate_expression(scope_idx, arg, loc)?);
+                }
+
+                match method.call(obj_value, arg_values) {
+                    Ok(result_val) => Ok(result_val),
+                    Err(method_err) => Err(InterpreterError::TypeError {
+                        context: format!("method call to {ident:?}"),
+                        conflict: format!("method error: {method_err}"),
+                        location: loc.clone(),
+                    }),
+                }
             }
             Expression::Variable { name, loc } => {
                 let locals = &self.scopes[scope_idx].variables;

hornbeam_interpreter/src/functions.rs

@@ -0,0 +1,23 @@
+use crate::interface::Value;
+
+pub(crate) mod defaults;
+
+/// A method that can be accessed (called) by templates.
+/// There is no dynamic dispatch for methods: the name of the method is the only thing that determines which one to call,
+/// not the type of the self-parameter.
+#[derive(Clone)]
+pub struct TemplateAccessibleMethod {
+    /// Function pointer that implements the method.
+    /// Arguments are:
+    /// - the 'self' parameter
+    /// - list of any parameters
+    ///
+    /// TODO Extend this to expose interpreter state.
+    function: fn(Value, Vec<Value>) -> Result<Value, String>,
+}
+
+impl TemplateAccessibleMethod {
+    pub(crate) fn call(&self, obj: Value, args: Vec<Value>) -> Result<Value, String> {
+        (self.function)(obj, args)
+    }
+}

hornbeam_interpreter/src/functions/defaults.rs

@@ -0,0 +1,74 @@
+use std::{collections::BTreeMap, sync::Arc};
+
+use percent_encoding::NON_ALPHANUMERIC;
+
+use crate::interface::Value;
+
+use super::TemplateAccessibleMethod;
+
+const DEFAULT_TEMPLATE_ACCESSIBLE_METHODS: &'static [(
+    &'static str,
+    fn(Value, Vec<Value>) -> Result<Value, String>,
+)] = &[("leftpad", leftpad), ("urlencode", urlencode)];
+
+/// Return a map of the default suggested template-accessible methods.
+pub fn default_template_accessible_methods() -> BTreeMap<String, TemplateAccessibleMethod> {
+    DEFAULT_TEMPLATE_ACCESSIBLE_METHODS
+        .iter()
+        .map(|(name, func)| {
+            (
+                (*name).to_owned(),
+                TemplateAccessibleMethod { function: *func },
+            )
+        })
+        .collect()
+}
+
+pub fn leftpad(obj: Value, args: Vec<Value>) -> Result<Value, String> {
+    let Value::Str(string_to_pad) = obj else {
+        return Err(format!("{obj:?} is not a string: can't leftpad!"));
+    };
+    if args.len() != 2 {
+        return Err(format!(
+            "leftpad takes 2 args (length, padding character), not {}",
+            args.len()
+        ));
+    }
+    let Value::Int(pad_length) = &args[0] else {
+        return Err(format!("leftpad's first arg should be an integer"));
+    };
+    let Value::Str(padding_character) = &args[1] else {
+        return Err(format!(
+            "leftpad's second arg should be a string (usually a single character)"
+        ));
+    };
+
+    if string_to_pad.len() as i64 >= *pad_length {
+        // zero-clone shortcut
+        // also required to prevent underflow!
+        return Ok(Value::Str(string_to_pad));
+    }
+
+    let repetitions = pad_length - string_to_pad.len() as i64;
+
+    let mut result = String::new();
+    for _ in 0..repetitions {
+        result.push_str(&padding_character);
+    }
+    result.push_str(&string_to_pad);
+
+    Ok(Value::Str(Arc::new(result)))
+}
+
+pub fn urlencode(obj: Value, args: Vec<Value>) -> Result<Value, String> {
+    let Value::Str(string_to_encode) = obj else {
+        return Err(format!("{obj:?} is not a string: can't urlencode!"));
+    };
+    if args.len() != 0 {
+        return Err(format!("urlencode takes 0 args, not {}", args.len()));
+    }
+
+    Ok(Value::Str(Arc::new(
+        percent_encoding::utf8_percent_encode(&string_to_encode, NON_ALPHANUMERIC).to_string(),
+    )))
+}

hornbeam_interpreter/src/interface.rs

@@ -1,4 +1,5 @@
 use crate::engine::{Interpreter, Scope};
+use crate::functions::TemplateAccessibleMethod;
 use async_trait::async_trait;
 use bevy_reflect::Reflect;
 use hornbeam_grammar::parse_template;
@@ -38,13 +39,15 @@ pub trait OutputSystem {
 
 // Value is currently used in the localisation system. We might pull it away later on...
 pub use crate::engine::Value;
-use crate::InterpreterError;
+use crate::{default_template_accessible_methods, InterpreterError};
 
 pub struct LoadedTemplates<LS> {
     // todo might be tempted to use e.g. ouroboros here, to keep the file source adjacent?
     // or do we just staticify?
     template_functions: BTreeMap<String, Arc<Vec<Step>>>,
 
+    methods: Arc<BTreeMap<String, TemplateAccessibleMethod>>,
+
     localisation: Arc<LS>,
 }
 
@@ -65,6 +68,7 @@ impl<'a, LS> LoadedTemplates<LS> {
     pub fn new(localisation_system: LS) -> Self {
         LoadedTemplates {
             template_functions: Default::default(),
+            methods: Arc::new(default_template_accessible_methods()),
             localisation: Arc::new(localisation_system),
         }
     }
@@ -161,12 +165,14 @@ impl<'a, LS> LoadedTemplates<LS> {
             variables: params,
             localisation: self.localisation.clone(),
             locale,
+            methods: self.methods.clone(),
         }
     }
 }
 
 pub struct PreparedTemplate<LS> {
     pub(crate) all_instructions: Arc<BTreeMap<String, Arc<Vec<Step>>>>,
+    pub(crate) methods: Arc<BTreeMap<String, TemplateAccessibleMethod>>,
     pub(crate) entrypoint: String,
     pub(crate) variables: Params,
     pub(crate) localisation: Arc<LS>,
@@ -188,6 +194,7 @@ impl<LS: LocalisationSystem + Sync + Send> PreparedTemplate<LS> {
                 variables: self.variables.params,
                 slots: Default::default(),
             }],
+            methods: &self.methods,
         };
         interpreter.run().await?;
         Ok(())

hornbeam_interpreter/src/lib.rs

@@ -1,6 +1,7 @@
 use std::fmt::Debug;
 
 mod engine;
+mod functions;
 pub(crate) mod interface;
 
 pub mod localisation;
@@ -36,4 +37,6 @@ pub enum InterpreterError<LE: Debug + Clone, OE: Debug> {
     TemplateFindError(String),
 }
 
+pub use functions::defaults::default_template_accessible_methods;
+pub use functions::TemplateAccessibleMethod;
 pub use interface::{LoadedTemplates, LocalisationSystem, OutputSystem, Params, PreparedTemplate};

hornbeam_interpreter/tests/snapshots.rs

@@ -15,7 +15,7 @@ fn simple_test_struct() -> SimpleTestStruct {
         wombat: 42,
         apple: 78,
         banana: "banana!!!".to_owned(),
-        carrot: "mmm CARROT".to_owned(),
+        carrot: "mmm CARROT!".to_owned(),
     }
 }
 
@@ -65,3 +65,16 @@ br
         "#
     ))
 }
+
+#[test]
+fn snapshot_003() {
+    assert_snapshot!(simple_render(
+        r#"
+"unpadded: ${$sts.carrot}"
+br
+"padded to 15: ${$sts.carrot.leftpad(15, 'M')}"
+br
+"urlencoded: ${$sts.carrot.urlencode()}"
+        "#
+    ))
+}

hornbeam_interpreter/tests/snapshots/snapshots__snapshot_003.snap

@@ -0,0 +1,5 @@
+---
+source: hornbeam_interpreter/tests/snapshots.rs
+expression: "simple_render(r#\"\n\"unpadded: ${$sts.carrot}\"\nbr\n\"padded to 15: ${$sts.carrot.leftpad(15, 'M')}\"\nbr\n\"urlencoded: ${$sts.carrot.urlencode()}\"\n        \"#)"
+---
+unpadded: mmm CARROT!<br>padded to 15: MMMMmmm CARROT!<br>urlencoded: mmm%20CARROT%21