Take default branch into account for changelog link

Author: jwodder

CHANGELOG.md

@@ -1,6 +1,8 @@
 v0.3.0 (in development)
 -----------------------
 - Switch from nom to winnow
+- `release`: Take name of repository's default branch into account when adding
+  changelog link to README
 
 v0.2.0 (2023-11-22)
 -------------------

src/commands/release.rs

@@ -43,6 +43,9 @@ impl Release {
             .context("Could not determine GitHub repository for local repository")?;
         let is_lib = package.is_lib()?;
         let publish = metadata.publish.as_deref() != Some(&[]);
+        let Some(default_branch) = git.default_branch()? else {
+            bail!("Could not determine repository's default branch");
+        };
 
         // Determine new version
         let new_version = if let Some(v) = self.version {
@@ -270,7 +273,7 @@ impl Release {
         let Some(mut readme) = readme_file.get()? else {
             bail!("README.md suddenly disappeared!");
         };
-        if readme.ensure_changelog_link(&ghrepo) {
+        if readme.ensure_changelog_link(&ghrepo, &default_branch) {
             log::info!("Adding Changelog link to README.md ...");
             readme_file.set(readme)?;
         }

src/git.rs

@@ -136,6 +136,19 @@ impl<'a> Git<'a> {
         }
         Ok(PathBuf::from(s))
     }
+
+    // Returns None if the default branch could not be determined
+    pub(crate) fn default_branch(&self) -> Result<Option<String>, CommandOutputError> {
+        let branches = self
+            .readlines("branch", ["--format=%(refname:short)"])?
+            .collect::<HashSet<_>>();
+        for guess in ["main", "master"] {
+            if branches.contains(guess) {
+                return Ok(Some(guess.to_owned()));
+            }
+        }
+        Ok(None)
+    }
 }
 
 #[cfg(test)]

src/readme.rs

@@ -103,12 +103,12 @@ impl Readme {
     }
 
     // Returns `true` if changed
-    pub(crate) fn ensure_changelog_link(&mut self, repo: &GHRepo) -> bool {
+    pub(crate) fn ensure_changelog_link(&mut self, repo: &GHRepo, default_branch: &str) -> bool {
         if self.links.iter().any(|lnk| lnk.text == "Changelog") {
             false
         } else {
             self.links.push(Link {
-                url: format!("https://github.com/{repo}/blob/master/CHANGELOG.md"),
+                url: format!("https://github.com/{repo}/blob/{default_branch}/CHANGELOG.md"),
                 text: "Changelog".into(),
             });
             true