Add support for git tags in --start and --end

Author: Kobzol

Diff for: src/git.rs

@@ -26,7 +26,21 @@ impl Commit {
 }
 
 fn lookup_rev<'rev>(repo: &'rev Repository, rev: &str) -> Result<Git2Commit<'rev>, Error> {
-    if let Ok(c) = repo.revparse_single(rev)?.into_commit() {
+    let revision = repo.revparse_single(rev)?;
+
+    // Find the merge-base between the revision and master.
+    // If revision is a normal commit contained in master, the merge-base will be the commit itself.
+    // If revision is a tag (e.g. a release version), the merge-base will contain the latest master
+    // commit contained in that tag.
+    let master_id = repo.revparse_single("origin/master")?.id();
+    let revision_id = revision
+        .as_tag()
+        .map(|tag| tag.target_id())
+        .unwrap_or_else(|| revision.id());
+
+    let common_base = repo.merge_base(master_id, revision_id)?;
+
+    if let Ok(c) = repo.find_commit(common_base) {
         return Ok(c);
     }
     bail!("Could not find a commit for revision specifier '{}'", rev)

Diff for: src/github.rs

@@ -4,6 +4,10 @@ use serde::{Deserialize, Serialize};
 
 use crate::Commit;
 
+#[derive(Serialize, Deserialize, Debug)]
+struct GithubCommitComparison {
+    merge_base_commit: GithubCommitElem,
+}
 #[derive(Serialize, Deserialize, Debug)]
 struct GithubCommitElem {
     commit: GithubCommit,
@@ -53,11 +57,11 @@ fn headers() -> Result<reqwest::header::HeaderMap, Error> {
 }
 
 pub(crate) fn get_commit(sha: &str) -> Result<Commit, Error> {
-    let url = SingleCommitUrl { sha }.url();
+    let url = CommitDetailsUrl { sha }.url();
     let client = Client::builder().default_headers(headers()?).build()?;
     let response: Response = client.get(&url).send()?;
-    let elem: GithubCommitElem = response.json()?;
-    elem.git_commit()
+    let elem: GithubCommitComparison = response.json()?;
+    elem.merge_base_commit.git_commit()
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -89,7 +93,7 @@ struct CommitsUrl<'a> {
     since: &'a str,
     sha: &'a str,
 }
-struct SingleCommitUrl<'a> {
+struct CommitDetailsUrl<'a> {
     sha: &'a str,
 }
 
@@ -110,25 +114,23 @@ impl<'a> ToUrl for CommitsUrl<'a> {
     }
 }
 
-impl<'a> ToUrl for SingleCommitUrl<'a> {
+impl<'a> ToUrl for CommitDetailsUrl<'a> {
     fn url(&self) -> String {
         // "origin/master" is set as `sha` when there is no `--end=` definition
         // specified on the command line.  We define the GitHub master branch
         // HEAD commit as the end commit in this case
-        if self.sha == "origin/master" {
-            format!(
-                "https://api.github.com/repos/{OWNER}/{REPO}/commits/master",
-                OWNER = OWNER,
-                REPO = REPO,
-            )
+        let reference = if self.sha == "origin/master" {
+            "master"
         } else {
-            format!(
-                "https://api.github.com/repos/{OWNER}/{REPO}/commits/{REF}",
-                OWNER = OWNER,
-                REPO = REPO,
-                REF = self.sha
-            )
-        }
+            self.sha
+        };
+
+        format!(
+            "https://api.github.com/repos/{OWNER}/{REPO}/compare/master...{REF}",
+            OWNER = OWNER,
+            REPO = REPO,
+            REF = reference
+        )
     }
 }