From a33bf73fe4abd49b3ff0debfaf71c28fc96db05c Mon Sep 17 00:00:00 2001
From: James Sully <sullyj3@gmail.com>
Date: Thu, 7 Sep 2023 16:24:40 +1000
Subject: [PATCH 1/2] revset: add ancestors_range() method

---
 lib/src/revset.rs | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/lib/src/revset.rs b/lib/src/revset.rs
index abc78d8e32..f2a16e858f 100644
--- a/lib/src/revset.rs
+++ b/lib/src/revset.rs
@@ -524,11 +524,7 @@ impl RevsetExpression {
 
     /// Ancestors of `self`, including `self`.
     pub fn ancestors(self: &Rc<RevsetExpression>) -> Rc<RevsetExpression> {
-        Rc::new(RevsetExpression::Ancestors {
-            heads: self.clone(),
-            generation: GENERATION_RANGE_FULL,
-            is_legacy: false,
-        })
+        self.ancestors_range(GENERATION_RANGE_FULL)
     }
     fn legacy_ancestors(self: &Rc<RevsetExpression>) -> Rc<RevsetExpression> {
         Rc::new(RevsetExpression::Ancestors {
@@ -540,9 +536,17 @@ impl RevsetExpression {
 
     /// Ancestors of `self`, including `self` until `generation` back.
     pub fn ancestors_at(self: &Rc<RevsetExpression>, generation: u64) -> Rc<RevsetExpression> {
+        self.ancestors_range(generation..(generation + 1))
+    }
+
+    /// Ancestors of `self` in the given range.
+    pub fn ancestors_range(
+        self: &Rc<RevsetExpression>,
+        generation_range: Range<u64>,
+    ) -> Rc<RevsetExpression> {
         Rc::new(RevsetExpression::Ancestors {
             heads: self.clone(),
-            generation: generation..(generation + 1),
+            generation: generation_range,
             is_legacy: false,
         })
     }

From b9b8706a8aa6f206af64eee67dc52ade7fe87b23 Mon Sep 17 00:00:00 2001
From: James Sully <sullyj3@gmail.com>
Date: Sat, 2 Sep 2023 16:02:35 +1000
Subject: [PATCH 2/2] revset: Add optional argument n to ancestors() in revset
 language

---
 CHANGELOG.md             |  4 ++++
 docs/revsets.md          |  4 +++-
 lib/src/revset.rs        | 12 +++++++++---
 lib/tests/test_revset.rs | 18 ++++++++++++++++++
 4 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 85192a89dd..7548cc62e8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### New features
 
+* The `ancestors()` revset function now takes an optional `depth` argument 
+  to limit the depth of the ancestor set. For example, use `jj log -r 
+  'ancestors(@, 5)` to view the last 5 commits.
+
 ### Fixed bugs
 
 ## [0.9.0] - 2023-09-06
diff --git a/docs/revsets.md b/docs/revsets.md
index b6ee6f97fd..c8101552c0 100644
--- a/docs/revsets.md
+++ b/docs/revsets.md
@@ -79,7 +79,9 @@ revsets (expressions) as arguments.
 
 * `parents(x)`: Same as `x-`.
 * `children(x)`: Same as `x+`.
-* `ancestors(x)`: Same as `:x`.
+* `ancestors(x[, depth])`: `ancestors(x)` is the same as `::x`. 
+  `ancestors(x, depth)` returns the ancestors of `x` limited to the given 
+  `depth`.
 * `descendants(x)`: Same as `x::`.
 * `connected(x)`: Same as `x::x`. Useful when `x` includes several commits.
 * `all()`: All visible commits in the repo.
diff --git a/lib/src/revset.rs b/lib/src/revset.rs
index f2a16e858f..aa899d52bc 100644
--- a/lib/src/revset.rs
+++ b/lib/src/revset.rs
@@ -1171,9 +1171,15 @@ static BUILTIN_FUNCTION_MAP: Lazy<HashMap<&'static str, RevsetFunction>> = Lazy:
         Ok(expression.children())
     });
     map.insert("ancestors", |name, arguments_pair, state| {
-        let arg = expect_one_argument(name, arguments_pair)?;
-        let expression = parse_expression_rule(arg.into_inner(), state)?;
-        Ok(expression.ancestors())
+        let ([heads_arg], [depth_opt_arg]) = expect_arguments(name, arguments_pair)?;
+        let heads = parse_expression_rule(heads_arg.into_inner(), state)?;
+        let generation = if let Some(depth_arg) = depth_opt_arg {
+            let depth = parse_function_argument_as_literal("integer", name, depth_arg, state)?;
+            0..depth
+        } else {
+            GENERATION_RANGE_FULL
+        };
+        Ok(heads.ancestors_range(generation))
     });
     map.insert("descendants", |name, arguments_pair, state| {
         let arg = expect_one_argument(name, arguments_pair)?;
diff --git a/lib/tests/test_revset.rs b/lib/tests/test_revset.rs
index e6696f1ae7..1dea99f10d 100644
--- a/lib/tests/test_revset.rs
+++ b/lib/tests/test_revset.rs
@@ -1205,6 +1205,24 @@ fn test_evaluate_expression_ancestors(use_git: bool) {
             root_commit.id().clone(),
         ]
     );
+
+    // Can find last n ancestors of a commit
+    assert_eq!(
+        resolve_commit_ids(mut_repo, &format!("ancestors({}, 0)", commit2.id().hex())),
+        vec![]
+    );
+    assert_eq!(
+        resolve_commit_ids(mut_repo, &format!("ancestors({}, 1)", commit3.id().hex())),
+        vec![commit3.id().clone()]
+    );
+    assert_eq!(
+        resolve_commit_ids(mut_repo, &format!("ancestors({}, 3)", commit3.id().hex())),
+        vec![
+            commit3.id().clone(),
+            commit2.id().clone(),
+            commit1.id().clone(),
+        ]
+    );
 }
 
 #[test_case(false ; "local backend")]