fix(vcs): Handle non-github workflow in find_base_sha

`find_head_sha` supported both Github workflow contexts and 'raw git'
contexts however the matching function `find_base_sha` did not handle
raw git contexts.

Thi updates `find_base_sha` to return the equivalent of:
`git merge-base HEAD origin/HEAD`. For:

```
     o---o---o---origin/main
    /
---1---o---o---o---foo
```

We return the SHA of 1.

Apply suggestion from @szokeasaurusrex

Co-authored-by: Daniel Szoke <7881302+szokeasaurusrex@users.noreply.github.com>

Update src/utils/vcs.rs

Co-authored-by: Daniel Szoke <7881302+szokeasaurusrex@users.noreply.github.com>

Author: chromy

CHANGELOG.md

@@ -7,6 +7,10 @@
 - Deprecated the `upload-proguard` subcommand's `--platform` flag ([#2863](https://github.com/getsentry/sentry-cli/pull/2863)). This flag appears to have been a no-op for some time, so we will remove it in the next major.
 - Deprecated the `upload-proguard` subcommand's `--android-manifest` flag ([#2891](https://github.com/getsentry/sentry-cli/pull/2891)). This flag appears to have been a no-op for some time, so we will remove it in the next major.
 
+### Fixes
+
+- Fix autofilled git base metadata (`--base-ref`, `--base-sha`) when using the `build upload` subcommand in git repos. Previously this worked only in the contexts of github workflows ([#2897](https://github.com/getsentry/sentry-cli/pull/2897))
+
 ## 2.57.0
 
 ### New Features

src/commands/build/upload.rs

@@ -233,7 +233,7 @@ pub fn execute(matches: &ArgMatches) -> Result<()> {
         .map(String::as_str)
         .map(Cow::Borrowed)
         .or_else(|| {
-            vcs::find_base_sha()
+            vcs::find_base_sha(&cached_remote)
                 .inspect_err(|e| debug!("Error finding base SHA: {e}"))
                 .ok()
                 .flatten()

src/utils/vcs.rs

@@ -569,13 +569,30 @@ pub fn find_head_sha() -> Result<String> {
     Ok(head.id().to_string())
 }
 
-pub fn find_base_sha() -> Result<Option<String>> {
-    let github_event = std::env::var("GITHUB_EVENT_PATH")
-        .map_err(Error::from)
-        .and_then(|event_path| std::fs::read_to_string(event_path).map_err(Error::from))
-        .context("Failed to read GitHub event path")?;
+pub fn find_base_sha(remote_name: &str) -> Result<Option<String>> {
+    if let Some(pr_base_sha) = std::env::var("GITHUB_EVENT_PATH")
+        .ok()
+        .and_then(|event_path| std::fs::read_to_string(event_path).ok())
+        .and_then(|content| extract_pr_base_sha_from_event(&content))
+    {
+        debug!("Using GitHub Actions PR base SHA from event payload: {pr_base_sha}");
+        return Ok(Some(pr_base_sha));
+    }
+
+    let repo = git2::Repository::open_from_env().context("Could not open repository")?;
+
+    let head_commit = repo.head()?.peel_to_commit()?;
 
-    Ok(extract_pr_base_sha_from_event(&github_event))
+    let remote_branch_name = format!("refs/remotes/{remote_name}/HEAD");
+    let remote_ref = repo
+        .find_reference(&remote_branch_name)
+        .with_context(|| "Could not find default branch for {remote_name}")?;
+
+    let remote_commit = remote_ref.peel_to_commit()?;
+    let merge_base_oid = repo.merge_base(head_commit.id(), remote_commit.id())?;
+    let merge_base_sha = merge_base_oid.to_string();
+    debug!("Found merge-base commit as base reference: {merge_base_sha}");
+    Ok(Some(merge_base_sha))
 }
 
 /// Extracts the PR head SHA from GitHub Actions event payload JSON.
@@ -1773,15 +1790,15 @@ mod tests {
         fs::write(&event_file, pr_json).expect("Failed to write event file");
         std::env::set_var("GITHUB_EVENT_PATH", event_file.to_str().unwrap());
 
-        let result = find_base_sha();
+        let result = find_base_sha("origin");
         assert_eq!(
             result.unwrap().unwrap(),
             "55e6bc8c264ce95164314275d805f477650c440d"
         );
 
         // Test without GITHUB_EVENT_PATH
         std::env::remove_var("GITHUB_EVENT_PATH");
-        let result = find_base_sha();
+        let result = find_base_sha("origin");
         assert!(result.is_err());
     }
 }