templater: do not implicitly add final newline character to commit.description

It's inconsistent that templater normalizes description whereas revset engine
doesn't. Since it's a UI/frontend matter to add the final newline when writing a
commit object, I don't think templater should implicitly modify the description.

Instead, this patch adds normalization to the builtin templates.

CHANGELOG.md

@@ -12,6 +12,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Breaking changes
 
+* Commit templates no longer normalize `description` by appending final newline
+  character. Use `description.trim_end() ++ "\n"` if needed.
+
 * Revset expressions like `hidden_id | description(x)` now [search the specified
   hidden revision and its ancestors](docs/revsets.md#hidden-revisions) as well
   as all visible revisions.

cli/src/commit_templater.rs

@@ -100,7 +100,6 @@ use crate::templater::Template;
 use crate::templater::TemplateFormatter;
 use crate::templater::TemplatePropertyError;
 use crate::templater::TemplatePropertyExt as _;
-use crate::text_util;
 
 pub trait CommitTemplateLanguageExtension {
     fn build_fn_table<'repo>(&self) -> CommitTemplateBuildFnTable<'repo>;
@@ -812,8 +811,7 @@ fn builtin_commit_methods<'repo>() -> CommitTemplateBuildMethodFnMap<'repo, Comm
         "description",
         |_language, _diagnostics, _build_ctx, self_property, function| {
             function.expect_no_arguments()?;
-            let out_property =
-                self_property.map(|commit| text_util::complete_newline(commit.description()));
+            let out_property = self_property.map(|commit| commit.description().to_owned());
             Ok(out_property.into_dyn_wrapped())
         },
     );

cli/src/config.rs

@@ -724,7 +724,7 @@ pub fn default_config_migrations() -> Vec<ConfigMigrationRule> {
             "template-aliases.default_commit_description",
             |old_value| {
                 let value = old_value.as_str().ok_or("expected a string")?;
-                // Trailing newline would be padded by templater
+                // Trailing newline would be padded by templater (in jj < 0.31)
                 let value = text_util::complete_newline(value);
                 let escaped = dsl_util::escape_string(&value);
                 Ok(format!(r#""{escaped}""#).into())

cli/src/config/templates.toml

@@ -170,7 +170,7 @@ if(root,
       separate(" ",
         if(empty, label("empty", "(empty)")),
         if(description,
-          description,
+          description.trim_end() ++ "\n",
           label(if(empty, "empty"), description_placeholder),
         ),
       ) ++ "\n",
@@ -192,7 +192,9 @@ concat(
     "Signature: " ++ format_detailed_cryptographic_signature(signature) ++ "\n"),
   "\n",
   indent("    ",
-    coalesce(description, label(if(empty, "empty"), description_placeholder) ++ "\n")),
+    if(description,
+      description.trim_end(),
+      label(if(empty, "empty"), description_placeholder)) ++ "\n"),
   "\n",
 )
 '''