cli: extract function that creates CommitTemplateLanguage for the wor…

…kspace

cmd_log() will parse the text and graph node templates by using the shared
language environment.

cli/src/cli_util.rs

@@ -912,15 +912,20 @@ Set which revision the branch points to with `jj branch set {branch_name} -r <RE
             }
         }
 
-        let language = CommitTemplateLanguage::new(
+        let language = self.commit_template_language()?;
+        let inner_template = self.parse_template(&language, template_text)?;
+        Ok(Box::new(TemplateWrapper(inner_template)))
+    }
+
+    /// Creates commit template language environment for this workspace.
+    pub fn commit_template_language(&self) -> Result<CommitTemplateLanguage<'_>, CommandError> {
+        Ok(CommitTemplateLanguage::new(
             self.repo().as_ref(),
             self.workspace_id(),
             self.revset_parse_context(),
             self.id_prefix_context()?,
             self.commit_template_extension.as_deref(),
-        );
-        let inner_template = self.parse_template(&language, template_text)?;
-        Ok(Box::new(TemplateWrapper(inner_template)))
+        ))
     }
 
     /// Template for one-line summary of a commit.