Merge pull request #388 from Kobzol/merge-base-doc

Clarify documentation around usage of merge-base

Author: ehuss

src/github.rs

@@ -82,6 +82,9 @@ fn headers() -> Result<HeaderMap, InvalidHeaderValue> {
     Ok(headers)
 }
 
+/// Lookup information about the given commit reference from GitHub.
+/// If it is a commit forked from the "mainline" git history (e.g. a stable tag
+/// like `1.88.0`), returns the merge base of the given commit reference.
 pub(crate) fn get_commit(sha: &str) -> anyhow::Result<Commit> {
     let url = CommitDetailsUrl { sha }.url();
     let client = Client::builder().default_headers(headers()?).build()?;

src/repo_access.rs

@@ -13,6 +13,8 @@ pub(crate) trait RustRepositoryAccessor {
 
     /// Looks up commit associated with `commit_ref`, which can be either a sha
     /// or a more general reference like "origin/master".
+    /// If `commit_ref` is a commit forked from the "mainline" git history
+    /// (e.g. a stable tag like `1.88.0`), returns the merge base of the given commit reference.
     fn commit(&self, commit_ref: &str) -> anyhow::Result<Commit>;
 
     /// Looks up a series of commits ending with `end_sha`; the resulting series