From 3a65c1d2ab56e8833218d24b2ce84ef1a384920e Mon Sep 17 00:00:00 2001
From: Martin von Zweigbergk <martinvonz@google.com>
Date: Sun, 18 Apr 2021 17:10:17 -0700
Subject: [PATCH] revsets: add intersection operator

---
 lib/src/revset.pest      |  3 ++-
 lib/src/revset.rs        | 58 ++++++++++++++++++++++++++++++++++++++++
 lib/tests/test_revset.rs | 49 +++++++++++++++++++++++++++++++++
 3 files changed, 109 insertions(+), 1 deletion(-)

diff --git a/lib/src/revset.pest b/lib/src/revset.pest
index 4f507edfa..e6395a134 100644
--- a/lib/src/revset.pest
+++ b/lib/src/revset.pest
@@ -21,8 +21,9 @@ ancestors = { "*:" }
 prefix_operator = _{ parents | ancestors }
 
 union = { "|" }
+intersection = { "&" }
 difference = { "-" }
-infix_operator = _{ union| difference }
+infix_operator = _{ union| intersection | difference }
 
 function_name = @{ (ASCII_ALPHANUMERIC | "_")+ }
 // The grammar accepts a string literal or an expression for function
diff --git a/lib/src/revset.rs b/lib/src/revset.rs
index a79116b6d..c9df8131d 100644
--- a/lib/src/revset.rs
+++ b/lib/src/revset.rs
@@ -108,6 +108,7 @@ pub enum RevsetExpression {
         base_expression: Box<RevsetExpression>,
     },
     Union(Box<RevsetExpression>, Box<RevsetExpression>),
+    Intersection(Box<RevsetExpression>, Box<RevsetExpression>),
     Difference(Box<RevsetExpression>, Box<RevsetExpression>),
 }
 
@@ -135,6 +136,10 @@ fn parse_infix_expression_rule(
             Rule::union => {
                 expression1 = RevsetExpression::Union(Box::new(expression1), Box::new(expression2))
             }
+            Rule::intersection => {
+                expression1 =
+                    RevsetExpression::Intersection(Box::new(expression1), Box::new(expression2))
+            }
             Rule::difference => {
                 expression1 =
                     RevsetExpression::Difference(Box::new(expression1), Box::new(expression2))
@@ -440,6 +445,54 @@ impl<'revset, 'repo> Iterator for UnionRevsetIterator<'revset, 'repo> {
     }
 }
 
+struct IntersectionRevset<'revset, 'repo: 'revset> {
+    set1: Box<dyn Revset<'repo> + 'revset>,
+    set2: Box<dyn Revset<'repo> + 'revset>,
+}
+
+impl<'repo> Revset<'repo> for IntersectionRevset<'_, 'repo> {
+    fn iter<'revset>(&'revset self) -> Box<dyn Iterator<Item = IndexEntry<'repo>> + 'revset> {
+        Box::new(IntersectionRevsetIterator {
+            iter1: self.set1.iter().peekable(),
+            iter2: self.set2.iter().peekable(),
+        })
+    }
+}
+
+struct IntersectionRevsetIterator<'revset, 'repo> {
+    iter1: Peekable<Box<dyn Iterator<Item = IndexEntry<'repo>> + 'revset>>,
+    iter2: Peekable<Box<dyn Iterator<Item = IndexEntry<'repo>> + 'revset>>,
+}
+
+impl<'revset, 'repo> Iterator for IntersectionRevsetIterator<'revset, 'repo> {
+    type Item = IndexEntry<'repo>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            match (self.iter1.peek(), self.iter2.peek()) {
+                (None, _) => {
+                    return None;
+                }
+                (_, None) => {
+                    return None;
+                }
+                (Some(entry1), Some(entry2)) => match entry1.position().cmp(&entry2.position()) {
+                    Ordering::Less => {
+                        self.iter2.next();
+                    }
+                    Ordering::Equal => {
+                        self.iter1.next();
+                        return self.iter2.next();
+                    }
+                    Ordering::Greater => {
+                        self.iter1.next();
+                    }
+                },
+            }
+        }
+    }
+}
+
 struct DifferenceRevset<'revset, 'repo: 'revset> {
     // The minuend (what to subtract from)
     set1: Box<dyn Revset<'repo> + 'revset>,
@@ -559,6 +612,11 @@ pub fn evaluate_expression<'revset, 'repo: 'revset>(
             let set2 = evaluate_expression(repo, expression2.as_ref())?;
             Ok(Box::new(UnionRevset { set1, set2 }))
         }
+        RevsetExpression::Intersection(expression1, expression2) => {
+            let set1 = evaluate_expression(repo, expression1.as_ref())?;
+            let set2 = evaluate_expression(repo, expression2.as_ref())?;
+            Ok(Box::new(IntersectionRevset { set1, set2 }))
+        }
         RevsetExpression::Difference(expression1, expression2) => {
             let set1 = evaluate_expression(repo, expression1.as_ref())?;
             let set2 = evaluate_expression(repo, expression2.as_ref())?;
diff --git a/lib/tests/test_revset.rs b/lib/tests/test_revset.rs
index 6c7b3cc4c..3e7869997 100644
--- a/lib/tests/test_revset.rs
+++ b/lib/tests/test_revset.rs
@@ -695,6 +695,55 @@ fn test_evaluate_expression_union(use_git: bool) {
     tx.discard();
 }
 
+#[test_case(false ; "local store")]
+#[test_case(true ; "git store")]
+fn test_evaluate_expression_intersection(use_git: bool) {
+    let settings = testutils::user_settings();
+    let (_temp_dir, repo) = testutils::init_repo(&settings, use_git);
+
+    let mut tx = repo.start_transaction("test");
+    let mut_repo = tx.mut_repo();
+
+    let root_commit = repo.store().root_commit();
+    let commit1 = testutils::create_random_commit(&settings, &repo).write_to_repo(mut_repo);
+    let commit2 = testutils::create_random_commit(&settings, &repo)
+        .set_parents(vec![commit1.id().clone()])
+        .write_to_repo(mut_repo);
+    let commit3 = testutils::create_random_commit(&settings, &repo)
+        .set_parents(vec![commit2.id().clone()])
+        .write_to_repo(mut_repo);
+    let commit4 = testutils::create_random_commit(&settings, &repo)
+        .set_parents(vec![commit3.id().clone()])
+        .write_to_repo(mut_repo);
+    let commit5 = testutils::create_random_commit(&settings, &repo)
+        .set_parents(vec![commit2.id().clone()])
+        .write_to_repo(mut_repo);
+
+    // Intersection between ancestors
+    assert_eq!(
+        resolve_commit_ids(
+            mut_repo.as_repo_ref(),
+            &format!("*:{} & *:{}", commit4.id().hex(), commit5.id().hex())
+        ),
+        vec![
+            commit2.id().clone(),
+            commit1.id().clone(),
+            root_commit.id().clone()
+        ]
+    );
+
+    // Intersection of disjoint sets
+    assert_eq!(
+        resolve_commit_ids(
+            mut_repo.as_repo_ref(),
+            &format!("{} & {}", commit4.id().hex(), commit2.id().hex())
+        ),
+        vec![]
+    );
+
+    tx.discard();
+}
+
 #[test_case(false ; "local store")]
 #[test_case(true ; "git store")]
 fn test_evaluate_expression_difference(use_git: bool) {