absorb: add basic support for file deletion

This works if the file was added and wasn't modified within the destination
range.

Closes #6140

CHANGELOG.md

@@ -49,6 +49,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 * Added `duplicate_description` template, which allows [customizing the descriptions
   of the commits `jj duplicate` creates](docs/config.md#duplicate-commit-description).
 
+* `jj absorb` can now squash a deleted file if it was added by one of the
+  destination revisions.
+
 ### Fixed bugs
 
 * Fixed crash on change-delete conflict resolution.

cli/tests/test_absorb_command.rs

@@ -479,15 +479,161 @@ fn test_absorb_deleted_file() {
 
     work_dir.run_jj(["describe", "-m1"]).success();
     work_dir.write_file("file1", "1a\n");
+    work_dir.write_file("file2", "1a\n");
+    work_dir.write_file("file3", "");
 
     work_dir.run_jj(["new"]).success();
     work_dir.remove_file("file1");
+    work_dir.write_file("file2", ""); // emptied
+    work_dir.remove_file("file3"); // no content change
 
+    // Since the destinations are chosen based on content diffs, file3 cannot be
+    // absorbed.
     let output = work_dir.run_jj(["absorb"]);
     insta::assert_snapshot!(output, @r"
     ------- stderr -------
-    Warning: Skipping file1: Deleted file
-    Nothing changed.
+    Absorbed changes into 1 revisions:
+      qpvuntsm f3c5cd48 1
+    Rebased 1 descendant commits.
+    Working copy  (@) now at: kkmpptxz 691fa544 (no description set)
+    Parent commit (@-)      : qpvuntsm f3c5cd48 1
+    Remaining changes:
+    D file3
+    [EOF]
+    ");
+
+    insta::assert_snapshot!(get_diffs(&work_dir, "mutable()"), @r"
+    @  kkmpptxz 691fa544 (no description set)
+    │  diff --git a/file3 b/file3
+    │  deleted file mode 100644
+    │  index e69de29bb2..0000000000
+    ○  qpvuntsm f3c5cd48 1
+    │  diff --git a/file2 b/file2
+    ~  new file mode 100644
+       index 0000000000..e69de29bb2
+       diff --git a/file3 b/file3
+       new file mode 100644
+       index 0000000000..e69de29bb2
+    [EOF]
+    ");
+}
+
+#[test]
+fn test_absorb_deleted_file_with_multiple_hunks() {
+    let test_env = TestEnvironment::default();
+    test_env.run_jj_in(".", ["git", "init", "repo"]).success();
+    let work_dir = test_env.work_dir("repo");
+
+    work_dir.run_jj(["describe", "-m1"]).success();
+    work_dir.write_file("file1", "1a\n1b\n");
+    work_dir.write_file("file2", "1a\n");
+
+    work_dir.run_jj(["new", "-m2"]).success();
+    work_dir.write_file("file1", "1a\n");
+    work_dir.write_file("file2", "1a\n1b\n");
+
+    // These changes produce conflicts because
+    // - for file1, "1a\n" is deleted from the commit 1,
+    // - for file2, two consecutive hunks are deleted.
+    //
+    // Since file2 change is split to two separate hunks, the file deletion
+    // cannot be propagated. If we implement merging based on interleaved delta,
+    // the file2 change will apply cleanly. The file1 change might be split into
+    // "1a\n" deletion at the commit 1 and file deletion at the commit 2, but
+    // I'm not sure if that's intuitive.
+    work_dir.run_jj(["new"]).success();
+    work_dir.remove_file("file1");
+    work_dir.remove_file("file2");
+    let output = work_dir.run_jj(["absorb"]);
+    insta::assert_snapshot!(output, @r"
+    ------- stderr -------
+    Absorbed changes into 2 revisions:
+      kkmpptxz ca0a3d3c (conflict) 2
+      qpvuntsm f2703d39 (conflict) 1
+    Rebased 1 descendant commits.
+    Working copy  (@) now at: zsuskuln 0156c3af (no description set)
+    Parent commit (@-)      : kkmpptxz ca0a3d3c (conflict) 2
+    New conflicts appeared in 2 commits:
+      kkmpptxz ca0a3d3c (conflict) 2
+      qpvuntsm f2703d39 (conflict) 1
+    Hint: To resolve the conflicts, start by updating to the first one:
+      jj new qpvuntsm
+    Then use `jj resolve`, or edit the conflict markers in the file directly.
+    Once the conflicts are resolved, you may want to inspect the result with `jj diff`.
+    Then run `jj squash` to move the resolution into the conflicted commit.
+    Remaining changes:
+    D file2
+    [EOF]
+    ");
+
+    insta::assert_snapshot!(get_diffs(&work_dir, "mutable()"), @r"
+    @  zsuskuln 0156c3af (no description set)
+    │  diff --git a/file2 b/file2
+    │  deleted file mode 100644
+    │  index 0000000000..0000000000
+    │  --- a/file2
+    │  +++ /dev/null
+    │  @@ -1,7 +0,0 @@
+    │  -<<<<<<< Conflict 1 of 1
+    │  -%%%%%%% Changes from base to side #1
+    │  --1a
+    │  - 1b
+    │  -+++++++ Contents of side #2
+    │  -1a
+    │  ->>>>>>> Conflict 1 of 1 ends
+    ×  kkmpptxz ca0a3d3c (conflict) 2
+    │  diff --git a/file1 b/file1
+    │  deleted file mode 100644
+    │  index 0000000000..0000000000
+    │  --- a/file1
+    │  +++ /dev/null
+    │  @@ -1,6 +0,0 @@
+    │  -<<<<<<< Conflict 1 of 1
+    │  -%%%%%%% Changes from base to side #1
+    │  - 1a
+    │  -+1b
+    │  -+++++++ Contents of side #2
+    │  ->>>>>>> Conflict 1 of 1 ends
+    │  diff --git a/file2 b/file2
+    │  --- a/file2
+    │  +++ b/file2
+    │  @@ -1,7 +1,7 @@
+    │   <<<<<<< Conflict 1 of 1
+    │   %%%%%%% Changes from base to side #1
+    │  - 1a
+    │  --1b
+    │  +-1a
+    │  + 1b
+    │   +++++++ Contents of side #2
+    │  -1b
+    │  +1a
+    │   >>>>>>> Conflict 1 of 1 ends
+    ×  qpvuntsm f2703d39 (conflict) 1
+    │  diff --git a/file1 b/file1
+    ~  new file mode 100644
+       index 0000000000..0000000000
+       --- /dev/null
+       +++ b/file1
+       @@ -0,0 +1,6 @@
+       +<<<<<<< Conflict 1 of 1
+       +%%%%%%% Changes from base to side #1
+       + 1a
+       ++1b
+       ++++++++ Contents of side #2
+       +>>>>>>> Conflict 1 of 1 ends
+       diff --git a/file2 b/file2
+       new file mode 100644
+       index 0000000000..0000000000
+       --- /dev/null
+       +++ b/file2
+       @@ -0,0 +1,7 @@
+       +<<<<<<< Conflict 1 of 1
+       +%%%%%%% Changes from base to side #1
+       + 1a
+       +-1b
+       ++++++++ Contents of side #2
+       +1b
+       +>>>>>>> Conflict 1 of 1 ends
     [EOF]
     ");
 }

lib/src/absorb.rs

@@ -117,17 +117,9 @@ pub async fn split_hunks_to_trees(
                 continue;
             }
         };
-        let right_text = match to_file_value(right_value) {
-            Ok(Some(mut value)) => value.read_all(right_path)?,
-            // Deleted file could be absorbed, but that would require special
-            // handling to propagate deletion of the tree entry
-            Ok(None) => {
-                let reason = "Deleted file".to_owned();
-                selected_trees
-                    .skipped_paths
-                    .push((right_path.to_owned(), reason));
-                continue;
-            }
+        let (right_text, deleted) = match to_file_value(right_value) {
+            Ok(Some(mut value)) => (value.read_all(right_path)?, false),
+            Ok(None) => (vec![], true),
             Err(reason) => {
                 selected_trees
                     .skipped_paths
@@ -157,14 +149,19 @@ pub async fn split_hunks_to_trees(
                 .entry(commit_id.clone())
                 .or_insert_with(|| MergedTreeBuilder::new(left_tree.id().clone()));
             let new_text = combine_texts(&left_text, &right_text, ranges);
-            let id = repo
-                .store()
-                .write_file(left_path, &mut new_text.as_slice())
-                .await?;
-            tree_builder.set_or_remove(
-                left_path.to_owned(),
-                Merge::normal(TreeValue::File { id, executable }),
-            );
+            // Since changes to be absorbed are represented as diffs relative to
+            // the source parent, we can propagate file deletion only if the
+            // whole file content is deleted at a single destination commit.
+            let new_tree_value = if new_text.is_empty() && deleted {
+                Merge::absent()
+            } else {
+                let id = repo
+                    .store()
+                    .write_file(left_path, &mut new_text.as_slice())
+                    .await?;
+                Merge::normal(TreeValue::File { id, executable })
+            };
+            tree_builder.set_or_remove(left_path.to_owned(), new_tree_value);
         }
     }