Add native reftable repository support

src/authorship/diff_base.rs

@@ -1,4 +1,18 @@
-pub(crate) const EMPTY_TREE_SHA: &str = "4b825dc642cb6eb9a060e54bf8d69288fbee4904";
+pub(crate) const SHA1_EMPTY_TREE: &str = "4b825dc642cb6eb9a060e54bf8d69288fbee4904";
+pub(crate) const SHA256_EMPTY_TREE: &str =
+    "6ef19b41225c5369f1c104d45d8d85efa9b057b53b14b4b9b939dd74decc5321";
+
+pub(crate) fn empty_tree_for_oid(oid: &str) -> &'static str {
+    if oid.len() == 64 {
+        SHA256_EMPTY_TREE
+    } else {
+        SHA1_EMPTY_TREE
+    }
+}
+
+pub(crate) fn is_empty_tree_oid(oid: &str) -> bool {
+    oid == SHA1_EMPTY_TREE || oid == SHA256_EMPTY_TREE
+}
 
 /// Resolve the diff base for post-commit diff parsing so the diff is always
 /// bounded to the single commit being finalized.
@@ -10,7 +24,7 @@ pub(crate) const EMPTY_TREE_SHA: &str = "4b825dc642cb6eb9a060e54bf8d69288fbee490
 /// tree hash because there is no parent revision.
 pub(crate) fn single_commit_diff_base(parent_sha: &str, commit_sha: &str) -> String {
     if parent_sha == "initial" {
-        EMPTY_TREE_SHA.to_string()
+        empty_tree_for_oid(commit_sha).to_string()
     } else {
         format!("{commit_sha}^")
     }

src/authorship/post_commit.rs

@@ -747,7 +747,7 @@ pub(crate) fn post_commit_amend_with_recovery_timestamps_detailed(
             | crate::authorship::background_agent::BackgroundAgent::WithHooks { .. }
     ) {
         let diff_base = if parent_sha == "initial" {
-            "4b825dc642cb6eb9a060e54bf8d69288fbee4904"
+            crate::authorship::diff_base::empty_tree_for_oid(amended_commit)
         } else {
             &parent_sha
         };
@@ -902,7 +902,7 @@ pub fn estimate_stats_cost_for_head(
             .map(|p| p.id())
             .unwrap_or_else(|_| "initial".to_string())
     } else {
-        "4b825dc642cb6eb9a060e54bf8d69288fbee4904".to_string()
+        crate::authorship::diff_base::empty_tree_for_oid(commit_sha).to_string()
     };
     estimate_stats_cost_for_commit_range(repo, &parent_sha, commit_sha, ignore_patterns)
 }

src/authorship/range_authorship.rs

@@ -223,7 +223,7 @@ fn create_authorship_log_for_range(
 
     // Special handling for empty tree: there's no start state to compare against
     // We only need the end state's attributions
-    if start_sha == EMPTY_TREE_HASH {
+    if crate::authorship::diff_base::is_empty_tree_oid(start_sha) {
         tracing::debug!("Start is empty tree - using only end commit attributions");
 
         let repo_clone = repo.clone();

src/authorship/rewrite.rs

@@ -10,8 +10,6 @@ use crate::git::repository::{
     Repository, exec_git, exec_git_allow_nonzero, exec_git_stdin_streaming,
 };
 
-const EMPTY_TREE_SHA: &str = "4b825dc642cb6eb9a060e54bf8d69288fbee4904";
-
 #[derive(Debug)]
 pub enum RewriteEvent {
     NonFastForward {
@@ -236,10 +234,6 @@ fn post_squash_metric_note_from_result(
     }
 }
 
-fn empty_tree_sha() -> &'static str {
-    EMPTY_TREE_SHA
-}
-
 fn tree_revision_arg(sha: &str) -> Option<String> {
     if sha == "initial" {
         None
@@ -248,9 +242,13 @@ fn tree_revision_arg(sha: &str) -> Option<String> {
     }
 }
 
-fn insert_known_tree(sha_to_tree: &mut HashMap<String, String>, sha: &str) -> bool {
+fn insert_known_tree(
+    sha_to_tree: &mut HashMap<String, String>,
+    sha: &str,
+    empty_tree: &str,
+) -> bool {
     if sha == "initial" {
-        sha_to_tree.insert(sha.to_string(), empty_tree_sha().to_string());
+        sha_to_tree.insert(sha.to_string(), empty_tree.to_string());
         true
     } else {
         false
@@ -277,9 +275,14 @@ fn resolve_tree_shas(
 ) -> Result<HashMap<String, String>, GitAiError> {
     let mut sha_to_tree = HashMap::new();
     let mut shas_to_resolve = Vec::new();
+    let empty_tree = unique_shas
+        .iter()
+        .find(|sha| sha.as_str() != "initial")
+        .map(|sha| crate::authorship::diff_base::empty_tree_for_oid(sha))
+        .unwrap_or(crate::authorship::diff_base::SHA1_EMPTY_TREE);
 
     for sha in unique_shas {
-        if !insert_known_tree(&mut sha_to_tree, sha) {
+        if !insert_known_tree(&mut sha_to_tree, sha, empty_tree) {
             shas_to_resolve.push(sha.clone());
         }
     }

src/authorship/stats.rs

@@ -511,7 +511,8 @@ pub fn stats_for_commit_stats_with_parent_and_authorship(
 ) -> Result<CommitStats, GitAiError> {
     use crate::commands::diff::get_diff_with_line_numbers;
 
-    let from_ref = parent_sha.unwrap_or("4b825dc642cb6eb9a060e54bf8d69288fbee4904");
+    let from_ref =
+        parent_sha.unwrap_or_else(|| crate::authorship::diff_base::empty_tree_for_oid(commit_sha));
     let hunks = get_diff_with_line_numbers(repo, from_ref, commit_sha)?;
     stats_for_commit_stats_from_hunks(repo, commit_sha, ignore_patterns, &hunks, authorship_log)
 }
@@ -686,7 +687,7 @@ pub fn get_git_diff_stats(
     }
 
     let from_ref = if parent_count == 0 {
-        "4b825dc642cb6eb9a060e54bf8d69288fbee4904".to_string()
+        crate::authorship::diff_base::empty_tree_for_oid(commit_sha).to_string()
     } else {
         commit_obj.parent(0)?.id()
     };

src/authorship/virtual_attribution.rs

@@ -1222,7 +1222,7 @@ fn collect_committed_hunks(
     // Handle initial commit (no parent)
     if parent_sha == "initial" {
         // For initial commit, use git diff against the empty tree
-        let empty_tree = "4b825dc642cb6eb9a060e54bf8d69288fbee4904"; // Git's empty tree hash
+        let empty_tree = crate::authorship::diff_base::empty_tree_for_oid(commit_sha);
         let added_lines = repo.diff_added_lines(empty_tree, commit_sha, pathspecs)?;
 
         for (file_path, lines) in added_lines {

src/commands/diff.rs

@@ -455,14 +455,14 @@ fn resolve_parent(repo: &Repository, commit: &str) -> Result<String, GitAiError>
 
             if sha.is_empty() {
                 // No parent, this is initial commit - use empty tree
-                Ok("4b825dc642cb6eb9a060e54bf8d69288fbee4904".to_string())
+                Ok(crate::authorship::diff_base::empty_tree_for_oid(commit).to_string())
             } else {
                 Ok(sha)
             }
         }
         Err(_) => {
             // No parent, this is initial commit - use empty tree hash
-            Ok("4b825dc642cb6eb9a060e54bf8d69288fbee4904".to_string())
+            Ok(crate::authorship::diff_base::empty_tree_for_oid(commit).to_string())
         }
     }
 }

src/commands/log.rs

@@ -663,7 +663,7 @@ fn render_stats(
     let parent_sha = parents
         .first()
         .map(String::as_str)
-        .unwrap_or("4b825dc642cb6eb9a060e54bf8d69288fbee4904");
+        .unwrap_or_else(|| crate::authorship::diff_base::empty_tree_for_oid(commit_sha));
 
     if let Ok(estimate) = crate::authorship::post_commit::estimate_stats_cost_for_commit_range(
         repo,