templates: add .email_domain() method to signatures TODO: test

This is slightly less pretty than making an Email type,
but I think is much easier.

I would use instead of the last argument of:

```
  concat(
    label("email", signature.username()),
    "@",
    label("email",
      signature.email().remove_prefix(
        signature.username() ++ "@"
      )
    )
  )
```

cli/src/template_builder.rs

@@ -787,6 +787,17 @@ fn builtin_signature_methods<'a, L: TemplateLanguage<'a> + ?Sized>(
             Ok(L::wrap_string(out_property))
         },
     );
+    map.insert(
+        "email_domain",
+        |_language, _diagnostics, _build_ctx, self_property, function| {
+            function.expect_no_arguments()?;
+            let out_property = self_property.map(|signature| {
+                let (_, domain) = text_util::split_email(&signature.email);
+                domain.unwrap_or_default().to_owned()
+            });
+            Ok(L::wrap_string(out_property))
+        },
+    );
     map.insert(
         "timestamp",
         |_language, _diagnostics, _build_ctx, self_property, function| {
@@ -2156,6 +2167,7 @@ mod tests {
         insta::assert_snapshot!(env.render_ok(r#"author.name()"#), @"Test User");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"[email protected]");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"test.user");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"example.com");
 
         env.add_keyword("author", || {
             L::wrap_signature(Literal(new_signature(
@@ -2167,6 +2179,7 @@ mod tests {
         insta::assert_snapshot!(env.render_ok(r#"author.name()"#), @"Another Test User");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"[email protected]");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"test.user");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"example.com");
 
         env.add_keyword("author", || {
             L::wrap_signature(Literal(new_signature(
@@ -2178,13 +2191,15 @@ mod tests {
         insta::assert_snapshot!(env.render_ok(r#"author.name()"#), @"Test User");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"test.user@[email protected]");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"test.user");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"[email protected]");
 
         env.add_keyword("author", || {
             L::wrap_signature(Literal(new_signature("Test User", "test.user")))
         });
         insta::assert_snapshot!(env.render_ok(r#"author"#), @"Test User <test.user>");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"test.user");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"test.user");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"");
 
         env.add_keyword("author", || {
             L::wrap_signature(Literal(new_signature(
@@ -2195,13 +2210,15 @@ mod tests {
         insta::assert_snapshot!(env.render_ok(r#"author"#), @"Test User <[email protected]>");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"[email protected]");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"test.user+tag");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"example.com");
 
         env.add_keyword("author", || {
             L::wrap_signature(Literal(new_signature("Test User", "x@y")))
         });
         insta::assert_snapshot!(env.render_ok(r#"author"#), @"Test User <x@y>");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"x@y");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"x");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"y");
 
         env.add_keyword("author", || {
             L::wrap_signature(Literal(new_signature("", "[email protected]")))
@@ -2210,6 +2227,7 @@ mod tests {
         insta::assert_snapshot!(env.render_ok(r#"author.name()"#), @"");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"[email protected]");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"test.user");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"example.com");
 
         env.add_keyword("author", || {
             L::wrap_signature(Literal(new_signature("Test User", "")))
@@ -2218,6 +2236,7 @@ mod tests {
         insta::assert_snapshot!(env.render_ok(r#"author.name()"#), @"Test User");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"");
 
         env.add_keyword("author", || {
             L::wrap_signature(Literal(new_signature("", "")))
@@ -2226,6 +2245,7 @@ mod tests {
         insta::assert_snapshot!(env.render_ok(r#"author.name()"#), @"");
         insta::assert_snapshot!(env.render_ok(r#"author.email()"#), @"");
         insta::assert_snapshot!(env.render_ok(r#"author.username()"#), @"");
+        insta::assert_snapshot!(env.render_ok(r#"author.email_domain()"#), @"");
     }
 
     #[test]

docs/templates.md

@@ -210,6 +210,7 @@ The following methods are defined.
 * `.name() -> String`
 * `.email() -> String`
 * `.username() -> String`
+* `.email_domain() -> String`: The part of the email after the `@`.
 * `.timestamp() -> Timestamp`
 
 ### SizeHint type