generic_templater: clone &Context to Self_ property like other languages

This prepares for removal of TemplateLanguage::Context type. "C: Clone" trait
bounds looked messy, but they can be removed soon.

cli/src/commands/config.rs

@@ -26,7 +26,7 @@ use crate::command_error::{user_error, CommandError};
 use crate::config::{AnnotatedValue, ConfigSource};
 use crate::generic_templater::GenericTemplateLanguage;
 use crate::template_builder::TemplateLanguage as _;
-use crate::templater::TemplatePropertyFn;
+use crate::templater::TemplateFunction;
 use crate::ui::Ui;
 
 #[derive(clap::Args, Clone, Debug)]
@@ -184,25 +184,28 @@ pub(crate) fn cmd_config(
     }
 }
 
+// AnnotatedValue will be cloned internally in the templater. If the cloning
+// cost matters, wrap it with Rc.
 fn config_template_language() -> GenericTemplateLanguage<'static, AnnotatedValue> {
     type L = GenericTemplateLanguage<'static, AnnotatedValue>;
-    fn prop_fn<R, F: Fn(&AnnotatedValue) -> R>(f: F) -> TemplatePropertyFn<F> {
-        TemplatePropertyFn(f)
-    }
-    let mut language = GenericTemplateLanguage::new();
+    let mut language = L::new();
     // "name" instead of "path" to avoid confusion with the source file path
-    language.add_keyword("name", || {
-        let property = prop_fn(|annotated| Ok(annotated.path.join(".")));
-        Ok(L::wrap_string(property))
+    language.add_keyword("name", |self_property| {
+        let out_property =
+            TemplateFunction::new(self_property, |annotated| Ok(annotated.path.join(".")));
+        Ok(L::wrap_string(out_property))
     });
-    language.add_keyword("value", || {
+    language.add_keyword("value", |self_property| {
         // TODO: would be nice if we can provide raw dynamically-typed value
-        let property = prop_fn(|annotated| Ok(serialize_config_value(&annotated.value)));
-        Ok(L::wrap_string(property))
+        let out_property = TemplateFunction::new(self_property, |annotated| {
+            Ok(serialize_config_value(&annotated.value))
+        });
+        Ok(L::wrap_string(out_property))
     });
-    language.add_keyword("overridden", || {
-        let property = prop_fn(|annotated| Ok(annotated.is_overridden));
-        Ok(L::wrap_boolean(property))
+    language.add_keyword("overridden", |self_property| {
+        let out_property =
+            TemplateFunction::new(self_property, |annotated| Ok(annotated.is_overridden));
+        Ok(L::wrap_boolean(out_property))
     });
     language
 }

cli/src/generic_templater.rs

@@ -19,19 +19,19 @@ use crate::template_builder::{
     TemplateLanguage,
 };
 use crate::template_parser::{self, FunctionCallNode, TemplateParseResult};
-use crate::templater::{Template, TemplateProperty};
+use crate::templater::{Template, TemplateProperty, TemplatePropertyFn};
 
 /// General-purpose template language for basic value types.
 ///
 /// This template language only supports the core template property types (plus
 /// the context type `C`.) The context type `C` is usually a tuple or struct of
-/// value types. Keyword functions need to be registered to extract properties
-/// from the context object.
-pub struct GenericTemplateLanguage<'a, C> {
+/// value types. It's cloned several times internally. Keyword functions need to
+/// be registered to extract properties from the context object.
+pub struct GenericTemplateLanguage<'a, C: Clone> {
     build_fn_table: GenericTemplateBuildFnTable<'a, C>,
 }
 
-impl<'a, C> GenericTemplateLanguage<'a, C> {
+impl<'a, C: Clone> GenericTemplateLanguage<'a, C> {
     /// Sets up environment with no keywords.
     ///
     /// New keyword functions can be registered by `add_keyword()`.
@@ -55,32 +55,33 @@ impl<'a, C> GenericTemplateLanguage<'a, C> {
     ///
     /// A keyword function returns `Self::Property`, which is basically a
     /// closure tagged by its return type. The inner closure is usually wrapped
-    /// by `TemplatePropertyFn`.
+    /// by `TemplateFunction`.
     ///
     /// ```ignore
-    /// language.add_keyword("name", || {
-    ///     let property = TemplatePropertyFn(|v: &C| Ok(v.to_string()));
-    ///     Ok(GenericTemplateLanguage::wrap_string(property))
+    /// language.add_keyword("name", |self_property| {
+    ///     let out_property = TemplateFunction::new(self_property, |v| Ok(v.to_string()));
+    ///     Ok(GenericTemplateLanguage::wrap_string(out_property))
     /// });
     /// ```
     pub fn add_keyword<F>(&mut self, name: &'static str, build: F)
     where
-        F: Fn() -> TemplateParseResult<GenericTemplatePropertyKind<'a, C>> + 'a,
+        F: Fn(
+                Box<dyn TemplateProperty<C, Output = C> + 'a>,
+            ) -> TemplateParseResult<GenericTemplatePropertyKind<'a, C>>
+            + 'a,
     {
         self.build_fn_table.keywords.insert(name, Box::new(build));
     }
 }
 
-impl<'a, C: 'a> TemplateLanguage<'a> for GenericTemplateLanguage<'a, C> {
+impl<'a, C: Clone + 'a> TemplateLanguage<'a> for GenericTemplateLanguage<'a, C> {
     type Context = C;
     type Property = GenericTemplatePropertyKind<'a, C>;
 
     template_builder::impl_core_wrap_property_fns!('a, GenericTemplatePropertyKind::Core);
 
     fn build_self(&self) -> Self::Property {
-        // No need to clone the context object because there are no other
-        // objects of "Self" type, and the context is available everywhere.
-        GenericTemplatePropertyKind::Self_
+        Self::wrap_self(TemplatePropertyFn(|context: &C| Ok(context.clone())))
     }
 
     fn build_function(
@@ -103,48 +104,56 @@ impl<'a, C: 'a> TemplateLanguage<'a> for GenericTemplateLanguage<'a, C> {
                 let table = &self.build_fn_table.core;
                 table.build_method(self, build_ctx, property, function)
             }
-            GenericTemplatePropertyKind::Self_ => {
+            GenericTemplatePropertyKind::Self_(property) => {
                 let table = &self.build_fn_table.keywords;
                 let build = template_parser::lookup_method("Self", table, function)?;
                 // For simplicity, only 0-ary method is supported.
                 template_parser::expect_no_arguments(function)?;
-                build()
+                build(property)
             }
         }
     }
 }
 
+impl<'a, C: Clone> GenericTemplateLanguage<'a, C> {
+    pub fn wrap_self(
+        property: impl TemplateProperty<C, Output = C> + 'a,
+    ) -> GenericTemplatePropertyKind<'a, C> {
+        GenericTemplatePropertyKind::Self_(Box::new(property))
+    }
+}
+
 pub enum GenericTemplatePropertyKind<'a, C> {
     Core(CoreTemplatePropertyKind<'a, C>),
-    Self_,
+    Self_(Box<dyn TemplateProperty<C, Output = C> + 'a>),
 }
 
 impl<'a, C: 'a> IntoTemplateProperty<'a, C> for GenericTemplatePropertyKind<'a, C> {
     fn try_into_boolean(self) -> Option<Box<dyn TemplateProperty<C, Output = bool> + 'a>> {
         match self {
             GenericTemplatePropertyKind::Core(property) => property.try_into_boolean(),
-            GenericTemplatePropertyKind::Self_ => None,
+            GenericTemplatePropertyKind::Self_(_) => None,
         }
     }
 
     fn try_into_integer(self) -> Option<Box<dyn TemplateProperty<C, Output = i64> + 'a>> {
         match self {
             GenericTemplatePropertyKind::Core(property) => property.try_into_integer(),
-            GenericTemplatePropertyKind::Self_ => None,
+            GenericTemplatePropertyKind::Self_(_) => None,
         }
     }
 
     fn try_into_plain_text(self) -> Option<Box<dyn TemplateProperty<C, Output = String> + 'a>> {
         match self {
             GenericTemplatePropertyKind::Core(property) => property.try_into_plain_text(),
-            GenericTemplatePropertyKind::Self_ => None,
+            GenericTemplatePropertyKind::Self_(_) => None,
         }
     }
 
     fn try_into_template(self) -> Option<Box<dyn Template<C> + 'a>> {
         match self {
             GenericTemplatePropertyKind::Core(property) => property.try_into_template(),
-            GenericTemplatePropertyKind::Self_ => None,
+            GenericTemplatePropertyKind::Self_(_) => None,
         }
     }
 }
@@ -154,15 +163,19 @@ impl<'a, C: 'a> IntoTemplateProperty<'a, C> for GenericTemplatePropertyKind<'a,
 ///
 /// Because the `GenericTemplateLanguage` doesn't provide a way to pass around
 /// global resources, the keyword function is allowed to capture resources.
-pub type GenericTemplateBuildKeywordFn<'a, C> =
-    Box<dyn Fn() -> TemplateParseResult<GenericTemplatePropertyKind<'a, C>> + 'a>;
+pub type GenericTemplateBuildKeywordFn<'a, C> = Box<
+    dyn Fn(
+            Box<dyn TemplateProperty<C, Output = C> + 'a>,
+        ) -> TemplateParseResult<GenericTemplatePropertyKind<'a, C>>
+        + 'a,
+>;
 
 /// Table of functions that translate keyword node.
 pub type GenericTemplateBuildKeywordFnMap<'a, C> =
     HashMap<&'static str, GenericTemplateBuildKeywordFn<'a, C>>;
 
 /// Symbol table of methods available in the general-purpose template.
-struct GenericTemplateBuildFnTable<'a, C: 'a> {
+struct GenericTemplateBuildFnTable<'a, C: Clone + 'a> {
     core: CoreTemplateBuildFnTable<'a, GenericTemplateLanguage<'a, C>>,
     keywords: GenericTemplateBuildKeywordFnMap<'a, C>,
 }

cli/src/template_builder.rs

@@ -1206,7 +1206,7 @@ mod tests {
         where
             F: Fn() -> TestTemplatePropertyKind + 'static,
         {
-            self.language.add_keyword(name, move || Ok(build()));
+            self.language.add_keyword(name, move |_| Ok(build()));
         }
 
         fn add_alias(&mut self, decl: impl AsRef<str>, defn: impl Into<String>) {