templater: add newtype to implement property over closure

Many template keywords and methods are one liners, and I think that's actually
good because writing tests for templater would be more involved than for pure
functions.

This patch introduces a wrapper for such one-line functions, and migrates
method parser to that. Some of the commit keyword structs can also be ported
to this wrapper.

src/template_parser.rs

@@ -24,12 +24,11 @@ use pest_derive::Parser;
 use crate::formatter::PlainTextFormatter;
 use crate::templater::{
     AuthorProperty, BranchProperty, ChangeIdProperty, CommitIdProperty, CommitOrChangeId,
-    CommitOrChangeIdShort, CommitOrChangeIdShortestPrefixAndBrackets, CommitterProperty,
-    ConditionalTemplate, ConflictProperty, DescriptionProperty, DivergentProperty,
-    DynamicLabelTemplate, EmptyProperty, FormattablePropertyTemplate, GitHeadProperty,
-    GitRefsProperty, HighlightPrefix, IdWithHighlightedPrefix, IsWorkingCopyProperty,
-    LabelTemplate, ListTemplate, Literal, SignatureTimestamp, TagProperty, Template,
-    TemplateFunction, TemplateProperty, WorkingCopiesProperty,
+    CommitterProperty, ConditionalTemplate, ConflictProperty, DescriptionProperty,
+    DivergentProperty, DynamicLabelTemplate, EmptyProperty, FormattablePropertyTemplate,
+    GitHeadProperty, GitRefsProperty, IdWithHighlightedPrefix, IsWorkingCopyProperty,
+    LabelTemplate, ListTemplate, Literal, TagProperty, Template, TemplateFunction,
+    TemplateProperty, TemplatePropertyFn, WorkingCopiesProperty,
 };
 use crate::time_util;
 
@@ -57,46 +56,6 @@ fn parse_string_literal(pair: Pair<Rule>) -> String {
     result
 }
 
-struct StringFirstLine;
-
-impl TemplateProperty<String> for StringFirstLine {
-    type Output = String;
-
-    fn extract(&self, context: &String) -> Self::Output {
-        context.lines().next().unwrap().to_string()
-    }
-}
-
-struct SignatureName;
-
-impl TemplateProperty<Signature> for SignatureName {
-    type Output = String;
-
-    fn extract(&self, context: &Signature) -> Self::Output {
-        context.name.clone()
-    }
-}
-
-struct SignatureEmail;
-
-impl TemplateProperty<Signature> for SignatureEmail {
-    type Output = String;
-
-    fn extract(&self, context: &Signature) -> Self::Output {
-        context.email.clone()
-    }
-}
-
-struct RelativeTimestampString;
-
-impl TemplateProperty<Timestamp> for RelativeTimestampString {
-    type Output = String;
-
-    fn extract(&self, context: &Timestamp) -> Self::Output {
-        time_util::format_timestamp_relative_to_now(context)
-    }
-}
-
 enum Property<'a, I> {
     String(Box<dyn TemplateProperty<I, Output = String> + 'a>),
     Boolean(Box<dyn TemplateProperty<I, Output = bool> + 'a>),
@@ -181,9 +140,14 @@ fn parse_method_chain<'a, I: 'a>(
 }
 
 fn parse_string_method<'a>(name: Pair<Rule>, _args: Pairs<Rule>) -> Property<'a, String> {
+    fn wrap_fn<'a, O>(
+        f: impl Fn(&String) -> O + 'a,
+    ) -> Box<dyn TemplateProperty<String, Output = O> + 'a> {
+        Box::new(TemplatePropertyFn(f))
+    }
     // TODO: validate arguments
     match name.as_str() {
-        "first_line" => Property::String(Box::new(StringFirstLine)),
+        "first_line" => Property::String(wrap_fn(|s| s.lines().next().unwrap().to_string())),
         name => panic!("no such string method: {name}"),
     }
 }
@@ -197,31 +161,48 @@ fn parse_commit_or_change_id_method<'a>(
     name: Pair<Rule>,
     _args: Pairs<Rule>,
 ) -> Property<'a, CommitOrChangeId<'a>> {
+    fn wrap_fn<'a, O>(
+        f: impl Fn(&CommitOrChangeId<'a>) -> O + 'a,
+    ) -> Box<dyn TemplateProperty<CommitOrChangeId<'a>, Output = O> + 'a> {
+        Box::new(TemplatePropertyFn(f))
+    }
     // TODO: validate arguments
     match name.as_str() {
-        "short" => Property::String(Box::new(CommitOrChangeIdShort)),
+        "short" => Property::String(wrap_fn(|id| id.short())),
         "shortest_prefix_and_brackets" => {
-            Property::String(Box::new(CommitOrChangeIdShortestPrefixAndBrackets))
+            Property::String(wrap_fn(|id| id.shortest_prefix_and_brackets()))
+        }
+        "shortest_styled_prefix" => {
+            Property::IdWithHighlightedPrefix(wrap_fn(|id| id.shortest_styled_prefix()))
         }
-        "shortest_styled_prefix" => Property::IdWithHighlightedPrefix(Box::new(HighlightPrefix)),
         name => panic!("no such commit ID method: {name}"),
     }
 }
 
 fn parse_signature_method<'a>(name: Pair<Rule>, _args: Pairs<Rule>) -> Property<'a, Signature> {
+    fn wrap_fn<'a, O>(
+        f: impl Fn(&Signature) -> O + 'a,
+    ) -> Box<dyn TemplateProperty<Signature, Output = O> + 'a> {
+        Box::new(TemplatePropertyFn(f))
+    }
     // TODO: validate arguments
     match name.as_str() {
-        "name" => Property::String(Box::new(SignatureName)),
-        "email" => Property::String(Box::new(SignatureEmail)),
-        "timestamp" => Property::Timestamp(Box::new(SignatureTimestamp)),
+        "name" => Property::String(wrap_fn(|signature| signature.name.clone())),
+        "email" => Property::String(wrap_fn(|signature| signature.email.clone())),
+        "timestamp" => Property::Timestamp(wrap_fn(|signature| signature.timestamp.clone())),
         name => panic!("no such commit ID method: {name}"),
     }
 }
 
 fn parse_timestamp_method<'a>(name: Pair<Rule>, _args: Pairs<Rule>) -> Property<'a, Timestamp> {
+    fn wrap_fn<'a, O>(
+        f: impl Fn(&Timestamp) -> O + 'a,
+    ) -> Box<dyn TemplateProperty<Timestamp, Output = O> + 'a> {
+        Box::new(TemplatePropertyFn(f))
+    }
     // TODO: validate arguments
     match name.as_str() {
-        "ago" => Property::String(Box::new(RelativeTimestampString)),
+        "ago" => Property::String(wrap_fn(time_util::format_timestamp_relative_to_now)),
         name => panic!("no such timestamp method: {name}"),
     }
 }

src/templater.rs

@@ -168,6 +168,17 @@ impl<C, O: Clone> TemplateProperty<C> for Literal<O> {
     }
 }
 
+/// Adapter to turn closure into property.
+pub struct TemplatePropertyFn<F>(pub F);
+
+impl<C, O, F: Fn(&C) -> O> TemplateProperty<C> for TemplatePropertyFn<F> {
+    type Output = O;
+
+    fn extract(&self, context: &C) -> Self::Output {
+        (self.0)(context)
+    }
+}
+
 /// Adapter to extract context-less template value from property for displaying.
 pub struct FormattablePropertyTemplate<P> {
     property: P,
@@ -494,7 +505,7 @@ impl CommitOrChangeId<'_> {
         hex
     }
 
-    fn shortest_prefix_and_brackets(&self) -> String {
+    pub fn shortest_prefix_and_brackets(&self) -> String {
         let hex = self.hex();
         let (prefix, rest) = extract_entire_prefix_and_trimmed_tail(
             &hex,
@@ -586,35 +597,6 @@ impl Template<()> for IdWithHighlightedPrefix {
     }
 }
 
-pub struct HighlightPrefix;
-impl TemplateProperty<CommitOrChangeId<'_>> for HighlightPrefix {
-    type Output = IdWithHighlightedPrefix;
-
-    fn extract(&self, context: &CommitOrChangeId) -> Self::Output {
-        context.shortest_styled_prefix()
-    }
-}
-
-pub struct CommitOrChangeIdShort;
-
-impl TemplateProperty<CommitOrChangeId<'_>> for CommitOrChangeIdShort {
-    type Output = String;
-
-    fn extract(&self, context: &CommitOrChangeId) -> Self::Output {
-        context.short()
-    }
-}
-
-pub struct CommitOrChangeIdShortestPrefixAndBrackets;
-
-impl TemplateProperty<CommitOrChangeId<'_>> for CommitOrChangeIdShortestPrefixAndBrackets {
-    type Output = String;
-
-    fn extract(&self, context: &CommitOrChangeId) -> Self::Output {
-        context.shortest_prefix_and_brackets()
-    }
-}
-
 pub struct CommitIdProperty<'a> {
     pub repo: RepoRef<'a>,
 }
@@ -645,16 +627,6 @@ impl<'a> TemplateProperty<Commit> for ChangeIdProperty<'a> {
     }
 }
 
-pub struct SignatureTimestamp;
-
-impl TemplateProperty<Signature> for SignatureTimestamp {
-    type Output = Timestamp;
-
-    fn extract(&self, context: &Signature) -> Self::Output {
-        context.timestamp.clone()
-    }
-}
-
 pub struct EmptyProperty<'a> {
     pub repo: RepoRef<'a>,
 }