fix(statistics): don't compute statistics when templates do not use them

git-cliff-core/src/config.rs

@@ -11,7 +11,8 @@ use serde::{Deserialize, Serialize};
 
 use crate::embed::EmbeddedConfig;
 use crate::error::Result;
-use crate::{CONFIG_FILES, DEFAULT_CONFIG, command, error};
+use crate::template::Template;
+use crate::{CONFIG_FILES, DEFAULT_CONFIG, command, error, statistics};
 
 /// Default initial tag.
 const DEFAULT_INITIAL_TAG: &str = "0.1.0";
@@ -560,6 +561,29 @@ impl Config {
             if path.is_file() { Some(path) } else { None }
         })
     }
+
+    /// Returns whether any configured changelog template references per-commit
+    /// diff statistics.
+    pub fn uses_commit_statistics(&self) -> Result<bool> {
+        let trim = self.changelog.trim;
+        let body_template = Template::new("body", self.changelog.body.clone(), trim)?;
+        if body_template.contains_variable(statistics::TEMPLATE_VARIABLES) {
+            return Ok(true);
+        }
+        if let Some(header) = &self.changelog.header {
+            let header_template = Template::new("header", header.clone(), trim)?;
+            if header_template.contains_variable(statistics::TEMPLATE_VARIABLES) {
+                return Ok(true);
+            }
+        }
+        if let Some(footer) = &self.changelog.footer {
+            let footer_template = Template::new("footer", footer.clone(), trim)?;
+            if footer_template.contains_variable(statistics::TEMPLATE_VARIABLES) {
+                return Ok(true);
+            }
+        }
+        Ok(false)
+    }
 }
 
 impl FromStr for Config {
@@ -668,4 +692,21 @@ mod test {
 
         Ok(())
     }
+
+    #[test]
+    fn detects_commit_statistics_usage_in_templates() -> Result<()> {
+        let mut config = EmbeddedConfig::parse()?;
+        assert!(!config.uses_commit_statistics()?);
+
+        config.changelog.body = String::from(
+            "{% for commit in commits %}{{ commit.statistics.files_changed }}{% endfor %}",
+        );
+        assert!(config.uses_commit_statistics()?);
+
+        config.changelog.body = String::from("{{ version }}");
+        config.changelog.footer = Some(String::from("{{ commit.statistics.additions }}"));
+        assert!(config.uses_commit_statistics()?);
+
+        Ok(())
+    }
 }

git-cliff-core/src/statistics.rs

@@ -5,6 +5,9 @@ use serde::{Deserialize, Serialize};
 
 use crate::release::Release;
 
+/// Template variables related to statistics context.
+pub(crate) const TEMPLATE_VARIABLES: &[&str] = &["commit.statistics"];
+
 /// Aggregated information about how many times a specific link appeared in
 /// commit messages.
 #[derive(Debug, Clone, Eq, PartialEq, Deserialize, Serialize)]

git-cliff/src/lib.rs

@@ -202,6 +202,7 @@ fn process_repository<'a>(
     let ignore_regex = config.git.ignore_tags.as_ref();
     let count_tags = config.git.count_tags.as_ref();
     let recurse_submodules = config.git.recurse_submodules.unwrap_or(false);
+    let compute_commit_statistics = config.uses_commit_statistics()?;
     tags.retain(|_, tag| {
         let name = &tag.name;
 
@@ -353,22 +354,25 @@ fn process_repository<'a>(
     for git_commit in commits.iter().rev() {
         let release = releases.last_mut().unwrap();
         let mut commit = Commit::from(git_commit);
-        commit.statistics = match repository.commit_statistics(git_commit) {
-            Ok(statistics) => statistics,
-            Err(err)
-                if matches!(
-                    &err,
-                    Error::GitError(git_err) if git_err.message().contains("object not found")
-                ) =>
-            {
-                tracing::warn!(
-                    "Skipping diff statistics for commit {} because a Git object is missing: {err}",
-                    commit.id,
-                );
-                CommitStatistics::default()
+        if compute_commit_statistics {
+            commit.statistics = match repository.commit_statistics(git_commit) {
+                Ok(statistics) => statistics,
+                Err(err)
+                    if matches!(
+                        &err,
+                        Error::GitError(git_err) if git_err.message().contains("object not found")
+                    ) =>
+                {
+                    tracing::warn!(
+                        "Skipping diff statistics for commit {} because a Git object is missing: \
+                         {err}",
+                        commit.id,
+                    );
+                    CommitStatistics::default()
+                }
+                Err(err) => return Err(err),
             }
-            Err(err) => return Err(err),
-        };
+        }
         let commit_id = commit.id.clone();
         release.commits.push(commit);
         release.repository = Some(repository_path.clone());