Move conflicted commit detection from headers to commit message markers

The `gitbutler-conflicted` extra header is stripped when commits are
rebased outside of GitButler, silently losing conflict state. Replace
it with commit message markers that survive rebasing and are visible
to developers in `git log`:

  - A `[conflict] ` prefix on the subject line for fast visual
    detection
  - A `GitButler-Conflict:` multi-line git trailer whose value
    explains the conflict tree layout

Using a standard git trailer means the description is embedded as the
trailer value with indented continuation lines, so
`git interpret-trailers` and other standard tools can parse and
manipulate it. The resulting commit message looks like:

    [conflict] <original subject>

    <original body>

    <existing trailers, if any>
    GitButler-Conflict: This is a GitButler-managed conflicted
       commit. Files are auto-resolved using the "ours" side.
       The commit tree contains additional directories:
         .conflict-side-0 — our tree
         .conflict-side-1 — their tree
         ...
       To manually resolve, check out this commit, remove the
       directories listed above, resolve the conflicts, and
       amend the commit.

The trailer is appended after any existing trailers in the message,
preserving Change-Id, Signed-off-by, and similar lines. When stripping
conflict markers (on resolution, display, or commit matching), the
prefix, trailer, and all continuation lines are removed to restore the
original message.

New commits only write message markers (no header). Reading checks the
message first, then falls back to the header for backward compatibility
with existing conflicted commits.

The CONFLICT-README.txt tree blob is removed since the trailer now
serves the same explanatory purpose with better visibility.

The conflicted file count (`Option<u64>`) stored in the old header was
only ever used as a boolean, so the new approach uses a simple presence
check with no count.

Author: mtsgrd

crates/but-core/src/commit.rs

@@ -29,6 +29,9 @@ git remote add origin normal-remote
 git remote add nested/remote nested-remote
 git remote add nested/remote-b nested-remote-b
 
+# NOTE: `git fetch` automatically creates remote HEAD refs (e.g.
+# refs/remotes/origin/HEAD) since git 2.48. Tests relying on these
+# refs require at least that version.
 git fetch origin
 git fetch nested/remote
 git fetch nested/remote-b

crates/but-core/tests/fixtures/scenario/multiple-remotes-with-tracking-branches.sh

@@ -23,7 +23,7 @@ pub enum EmptyCommit {
 }
 
 pub(crate) mod function {
-    use std::{collections::HashSet, path::PathBuf};
+    use std::path::PathBuf;
 
     use anyhow::{Context as _, bail};
     use bstr::BString;
@@ -168,18 +168,22 @@ pub(crate) mod function {
         }
 
         let headers = to_rebase.headers();
-        let to_rebase_is_conflicted = headers.as_ref().is_some_and(|hdr| hdr.is_conflicted());
+        let was_conflicted = to_rebase.is_conflicted();
         let mut new_commit = to_rebase.inner;
         new_commit.tree = resolved_tree_id.detach();
 
         // Assure the commit isn't thinking it's conflicted.
-        if to_rebase_is_conflicted {
+        if was_conflicted {
+            // Strip the legacy header if present
             if let Some(pos) = new_commit
                 .extra_headers()
                 .find_pos(HEADERS_CONFLICTED_FIELD)
             {
                 new_commit.extra_headers.remove(pos);
             }
+            // Strip conflict markers from the commit message
+            new_commit.message =
+                but_core::commit::strip_conflict_markers(new_commit.message.as_ref());
         } else if headers.is_none() {
             let headers = Headers::from_config(&repo.config_snapshot());
             new_commit
@@ -204,10 +208,6 @@ pub(crate) mod function {
         treat_as_unresolved: gix::merge::tree::TreatAsUnresolved,
     ) -> anyhow::Result<gix::Id<'repo>> {
         let repo = resolved_tree_id.repo;
-        // in case someone checks this out with vanilla Git, we should warn why it looks like this
-        let readme_content =
-            b"You have checked out a GitButler Conflicted commit. You probably didn't mean to do this.";
-        let readme_blob = repo.write_blob(readme_content)?;
 
         let conflicted_files =
             extract_conflicted_files(resolved_tree_id, cherry_pick, treat_as_unresolved)?;
@@ -242,15 +242,20 @@ pub(crate) mod function {
             resolved_tree_id,
         )?;
         tree.upsert(".conflict-files", EntryKind::Blob, conflicted_files_blob)?;
-        tree.upsert("CONFLICT-README.txt", EntryKind::Blob, readme_blob)?;
 
         let mut headers = to_rebase
             .headers()
             .unwrap_or_else(|| Headers::from_config(&repo.config_snapshot()));
-        headers.conflicted = conflicted_files.conflicted_header_field();
+        headers.conflicted = None;
         to_rebase.tree = tree.write().context("failed to write tree")?.detach();
         set_parent(&mut to_rebase, head.id.detach())?;
 
+        // Add conflict markers to the commit message
+        if !but_core::commit::message_is_conflicted(to_rebase.inner.message.as_ref()) {
+            to_rebase.inner.message =
+                but_core::commit::add_conflict_markers(to_rebase.inner.message.as_ref());
+        }
+
         to_rebase.set_headers(&headers);
         Ok(crate::commit::create(
             repo,
@@ -341,22 +346,5 @@ pub(crate) mod function {
                 || !self.our_entries.is_empty()
                 || !self.their_entries.is_empty()
         }
-
-        fn total_entries(&self) -> usize {
-            let set = self
-                .ancestor_entries
-                .iter()
-                .chain(self.our_entries.iter())
-                .chain(self.their_entries.iter())
-                .collect::<HashSet<_>>();
-
-            set.len()
-        }
-
-        /// Return the `conflicted` header field value.
-        pub(crate) fn conflicted_header_field(&self) -> Option<u64> {
-            let entries = self.total_entries();
-            Some(if entries > 0 { entries as u64 } else { 1 })
-        }
     }
 }

crates/but-rebase/src/cherry_pick.rs

@@ -305,18 +305,21 @@ fn commit_from_unconflicted_tree<'repo>(
     let repo = to_rebase.id.repo;
 
     let headers = to_rebase.headers();
-    let to_rebase_is_conflicted = headers.as_ref().is_some_and(|hdr| hdr.is_conflicted());
+    let was_conflicted = to_rebase.is_conflicted();
     let mut new_commit = to_rebase.inner;
     new_commit.tree = resolved_tree_id.detach();
 
     // Ensure the commit isn't thinking it's conflicted.
-    if to_rebase_is_conflicted {
+    if was_conflicted {
+        // Strip the legacy header if present
         if let Some(pos) = new_commit
             .extra_headers()
             .find_pos(HEADERS_CONFLICTED_FIELD)
         {
             new_commit.extra_headers.remove(pos);
         }
+        // Strip conflict markers from the commit message
+        new_commit.message = but_core::commit::strip_conflict_markers(new_commit.message.as_ref());
     } else if headers.is_none() {
         let headers = Headers::from_config(&repo.config_snapshot());
         new_commit
@@ -347,10 +350,6 @@ fn commit_from_conflicted_tree<'repo>(
     sign_commit: SignCommit,
 ) -> anyhow::Result<gix::Id<'repo>> {
     let repo = resolved_tree_id.repo;
-    // in case someone checks this out with vanilla Git, we should warn why it looks like this
-    let readme_content =
-        b"You have checked out a GitButler Conflicted commit. You probably didn't mean to do this.";
-    let readme_blob = repo.write_blob(readme_content)?;
 
     let conflicted_files =
         extract_conflicted_files(resolved_tree_id, cherry_pick, treat_as_unresolved)?;
@@ -382,15 +381,20 @@ fn commit_from_conflicted_tree<'repo>(
         resolved_tree_id,
     )?;
     tree.upsert(".conflict-files", EntryKind::Blob, conflicted_files_blob)?;
-    tree.upsert("CONFLICT-README.txt", EntryKind::Blob, readme_blob)?;
 
     let mut headers = to_rebase
         .headers()
         .unwrap_or_else(|| Headers::from_config(&repo.config_snapshot()));
-    headers.conflicted = conflicted_files.conflicted_header_field();
+    headers.conflicted = None;
     to_rebase.tree = tree.write().context("failed to write tree")?.detach();
     to_rebase.parents = parents.into();
 
+    // Add conflict markers to the commit message
+    if !but_core::commit::message_is_conflicted(to_rebase.inner.message.as_ref()) {
+        to_rebase.inner.message =
+            but_core::commit::add_conflict_markers(to_rebase.inner.message.as_ref());
+    }
+
     to_rebase.set_headers(&headers);
     Ok(crate::commit::create(
         repo,

crates/but-rebase/src/graph_rebase/cherry_pick.rs

@@ -286,7 +286,11 @@ fn rebase(
                         None if commit.parents.is_empty() => {
                             let mut new_commit = commit;
                             if let Some(new_message) = new_message {
-                                new_commit.message = new_message;
+                                new_commit.message =
+                                    but_core::commit::rewrite_conflict_markers_on_message_change(
+                                        new_commit.message.as_ref(),
+                                        new_message,
+                                    );
                             }
                             cursor = Some(commit::create(
                                 repo,
@@ -325,7 +329,11 @@ fn rebase(
                 let mut new_commit = repo.find_commit(new_commit)?.decode()?.to_owned()?;
                 new_commit.parents = base_commit.parent_ids().map(|id| id.detach()).collect();
                 if let Some(new_message) = new_message {
-                    new_commit.message = new_message;
+                    new_commit.message =
+                        but_core::commit::rewrite_conflict_markers_on_message_change(
+                            new_commit.message.as_ref(),
+                            new_message,
+                        );
                 }
                 *cursor = commit::create(
                     repo,
@@ -371,7 +379,10 @@ fn reword_commit(
     new_message: BString,
 ) -> Result<gix::ObjectId> {
     let mut new_commit = repo.find_commit(oid)?.decode()?.to_owned()?;
-    new_commit.message = new_message;
+    new_commit.message = but_core::commit::rewrite_conflict_markers_on_message_change(
+        new_commit.message.as_ref(),
+        new_message,
+    );
     Ok(commit::create(
         repo,
         new_commit,

crates/but-rebase/src/lib.rs

@@ -69,7 +69,7 @@ fn basic_cherry_pick_cp_conflicts() -> Result<()> {
 
     insta::assert_debug_snapshot!(result, @"
     ConflictedCommit(
-        Sha1(e9ee7b59aff786fc970c30f6965d1de1913c7ec4),
+        Sha1(9661555c611ff64e8c597f7f5a0575f211eb2e12),
     )
     ");
 
@@ -80,7 +80,7 @@ fn basic_cherry_pick_cp_conflicts() -> Result<()> {
     assert_eq!(&get_parents(&id.attach(&repo))?, &[onto]);
 
     insta::assert_snapshot!(visualize_tree(id.attach(&repo)), @r#"
-    0367fb7
+    1090f8a
     ├── .auto-resolution:aa3d213 
     │   ├── base-f:100644:7898192 "a\n"
     │   └── target-f:100644:eb5a316 "target\n"
@@ -95,7 +95,6 @@ fn basic_cherry_pick_cp_conflicts() -> Result<()> {
     │   ├── base-f:100644:7898192 "a\n"
     │   ├── clean-f:100644:8312630 "clean\n"
     │   └── target-f:100644:9b1719f "conflict\n"
-    ├── CONFLICT-README.txt:100644:2af04b7 "You have checked out a GitButler Conflicted commit. You probably didn\'t mean to do this."
     ├── base-f:100644:7898192 "a\n"
     └── target-f:100644:eb5a316 "target\n"
     "#);
@@ -184,7 +183,7 @@ fn single_parent_to_multiple_parents_cp_conflicts() -> Result<()> {
 
     insta::assert_debug_snapshot!(result, @"
     ConflictedCommit(
-        Sha1(0fcbe01202743fa55f1a1e07342ad26f2e7a0abe),
+        Sha1(c8779c405b92941176effe9eb7a72c0dd410c3fd),
     )
     ");
 
@@ -195,7 +194,7 @@ fn single_parent_to_multiple_parents_cp_conflicts() -> Result<()> {
     assert_eq!(&get_parents(&id.attach(&repo))?, &[onto, onto2]);
 
     insta::assert_snapshot!(visualize_tree(id.attach(&repo)), @r#"
-    1804f3d
+    4c6dc70
     ├── .auto-resolution:744efa9 
     │   ├── base-f:100644:7898192 "a\n"
     │   ├── target-2-f:100644:caac8f9 "target 2\n"
@@ -212,7 +211,6 @@ fn single_parent_to_multiple_parents_cp_conflicts() -> Result<()> {
     │   ├── base-f:100644:7898192 "a\n"
     │   ├── clean-f:100644:8312630 "clean\n"
     │   └── target-f:100644:9b1719f "conflict\n"
-    ├── CONFLICT-README.txt:100644:2af04b7 "You have checked out a GitButler Conflicted commit. You probably didn\'t mean to do this."
     ├── base-f:100644:7898192 "a\n"
     ├── target-2-f:100644:caac8f9 "target 2\n"
     └── target-f:100644:eb5a316 "target\n"
@@ -311,7 +309,7 @@ fn multiple_parents_to_single_parent_cp_conflicts() -> Result<()> {
 
     insta::assert_debug_snapshot!(result, @"
     ConflictedCommit(
-        Sha1(28fa7c91af8652f4e69c1e3184f92569a3468a34),
+        Sha1(2d4dcd916020924f2412642b842a791dfea74571),
     )
     ");
 
@@ -322,7 +320,7 @@ fn multiple_parents_to_single_parent_cp_conflicts() -> Result<()> {
     assert_eq!(&get_parents(&id.attach(&repo))?, &[onto]);
 
     insta::assert_snapshot!(visualize_tree(id.attach(&repo)), @r#"
-    91fe014
+    8c4acd1
     ├── .auto-resolution:aa3d213 
     │   ├── base-f:100644:7898192 "a\n"
     │   └── target-f:100644:eb5a316 "target\n"
@@ -339,7 +337,6 @@ fn multiple_parents_to_single_parent_cp_conflicts() -> Result<()> {
     │   ├── clean-2-f:100644:13e9394 "clean 2\n"
     │   ├── clean-f:100644:8312630 "clean\n"
     │   └── target-f:100644:9b1719f "conflict\n"
-    ├── CONFLICT-README.txt:100644:2af04b7 "You have checked out a GitButler Conflicted commit. You probably didn\'t mean to do this."
     ├── base-f:100644:7898192 "a\n"
     └── target-f:100644:eb5a316 "target\n"
     "#);
@@ -441,7 +438,7 @@ fn multiple_parents_to_multiple_parents_cp_conflicts() -> Result<()> {
 
     insta::assert_debug_snapshot!(result, @"
     ConflictedCommit(
-        Sha1(2e6cb06fe98780bb8c7a301a522edd98805d1499),
+        Sha1(bf66deb17cc4e84faa063a3253566004aabaf7fe),
     )
     ");
 
@@ -452,7 +449,7 @@ fn multiple_parents_to_multiple_parents_cp_conflicts() -> Result<()> {
     assert_eq!(&get_parents(&id.attach(&repo))?, &[onto, onto2]);
 
     insta::assert_snapshot!(visualize_tree(id.attach(&repo)), @r#"
-    0aeaf79
+    1620d95
     ├── .auto-resolution:744efa9 
     │   ├── base-f:100644:7898192 "a\n"
     │   ├── target-2-f:100644:caac8f9 "target 2\n"
@@ -471,7 +468,6 @@ fn multiple_parents_to_multiple_parents_cp_conflicts() -> Result<()> {
     │   ├── clean-2-f:100644:13e9394 "clean 2\n"
     │   ├── clean-f:100644:8312630 "clean\n"
     │   └── target-f:100644:9b1719f "conflict\n"
-    ├── CONFLICT-README.txt:100644:2af04b7 "You have checked out a GitButler Conflicted commit. You probably didn\'t mean to do this."
     ├── base-f:100644:7898192 "a\n"
     ├── target-2-f:100644:caac8f9 "target 2\n"
     └── target-f:100644:eb5a316 "target\n"
@@ -688,7 +684,7 @@ fn no_parents_to_single_parent_cp_conflicts() -> Result<()> {
 
     insta::assert_debug_snapshot!(result, @"
     ConflictedCommit(
-        Sha1(28f862257bff139659b763a2c873b8d3f0f780b0),
+        Sha1(2ee47b5cbe2705d5d81f4b4067ef4753d87b3b02),
     )
     ");
 
@@ -699,7 +695,7 @@ fn no_parents_to_single_parent_cp_conflicts() -> Result<()> {
     assert_eq!(&get_parents(&id.attach(&repo))?, &[onto]);
 
     insta::assert_snapshot!(visualize_tree(id.attach(&repo)), @r#"
-    1267a55
+    38edd44
     ├── .auto-resolution:aa3d213 
     │   ├── base-f:100644:7898192 "a\n"
     │   └── target-f:100644:eb5a316 "target\n"
@@ -711,7 +707,6 @@ fn no_parents_to_single_parent_cp_conflicts() -> Result<()> {
     ├── .conflict-side-1:144e5f5 
     │   ├── base-f:100644:7898192 "a\n"
     │   └── target-f:100644:9b1719f "conflict\n"
-    ├── CONFLICT-README.txt:100644:2af04b7 "You have checked out a GitButler Conflicted commit. You probably didn\'t mean to do this."
     ├── base-f:100644:7898192 "a\n"
     └── target-f:100644:eb5a316 "target\n"
     "#);
@@ -738,7 +733,7 @@ fn cherry_pick_back_to_original_parents_unconflicts() -> Result<()> {
 
     insta::assert_debug_snapshot!(result, @"
     ConflictedCommit(
-        Sha1(2e6cb06fe98780bb8c7a301a522edd98805d1499),
+        Sha1(bf66deb17cc4e84faa063a3253566004aabaf7fe),
     )
     ");
 
@@ -758,7 +753,7 @@ fn cherry_pick_back_to_original_parents_unconflicts() -> Result<()> {
 
     insta::assert_debug_snapshot!(result, @"
     Commit(
-        Sha1(3d7dfa09a071658d3b84eb1ee195ea0ebfeb601f),
+        Sha1(2a307db18bf263e3a802ac71282c5d8016ea75a1),
     )
     ");
 

crates/but-rebase/tests/rebase/graph_rebase/cherry_pick.rs

@@ -36,7 +36,7 @@ fn by_default_conflicts_are_allowed() -> Result<()> {
     insta::assert_snapshot!(overlayed, @"
 
     └── 👉►:0[0]:main[🌳]
-        ├── ·3411540 (⌂|1) ►c
+        ├── ·103b227 (⌂|1) ►c
         └── ·5e0ba46 (⌂|1) ►a, ►b
             └── ►:1[1]:base
                 └── ·6155f21 (⌂|1)
@@ -45,17 +45,26 @@ fn by_default_conflicts_are_allowed() -> Result<()> {
     assert_eq!(overlayed, graph_tree(&outcome.workspace.graph).to_string());
 
     // We expect to see conflicted headers
-    insta::assert_snapshot!(cat_commit(&repo, "c")?, @"
-    tree c199bde16a034b8588f7c896ec3640c40ad017dd
+    insta::assert_snapshot!(cat_commit(&repo, "c")?, @r#"
+    tree d935c009623a61ebde94512baef22c76c5ccbaef
     parent 5e0ba4636be91de6216903697b269915d3db6c53
     author author <author@example.com> 946684800 +0000
     committer Committer (Memory Override) <committer@example.com> 946771200 +0000
     gitbutler-headers-version 2
     change-id 1
-    gitbutler-conflicted 1
 
-    c
-    ");
+    [conflict] c
+
+    GitButler-Conflict: This is a GitButler-managed conflicted commit. Files are auto-resolved
+       using the "ours" side. The commit tree contains additional directories:
+         .conflict-side-0  — our tree
+         .conflict-side-1  — their tree
+         .conflict-base-0  — the merge base tree
+         .auto-resolution  — the auto-resolved tree
+         .conflict-files   — metadata about conflicted files
+       To manually resolve, check out this commit, remove the directories
+       listed above, resolve the conflicts, and amend the commit.
+    "#);
 
     Ok(())
 }