From d4814aa84094d381728e32ec2d86cd9bd72ec0d2 Mon Sep 17 00:00:00 2001
From: Anton Geraschenko <geraschenko@gmail.com>
Date: Sun, 26 Apr 2026 14:13:38 -0700
Subject: [PATCH] renderdag: emit link_line for same-column named parents
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With `min_row_height(1)`, connected and disconnected same-column adjacent nodes render identically, with no `│` between connected nodes. See #1292.

Before / After (box_drawing, min_row_height=1) for new `BASIC_DISCONNECTED` fixture (`dag: "A B-C"`, heads `["A", "C"]`):
```
Before:
o  C
o  B
o  A

After:
o  C
│
o  B
o  A
```
---
 eden/scm/lib/renderdag/src/ascii.rs         | 29 +++++++++++++++++++++
 eden/scm/lib/renderdag/src/ascii_large.rs   | 15 +++++++++++
 eden/scm/lib/renderdag/src/box_drawing.rs   | 29 +++++++++++++++++++++
 eden/scm/lib/renderdag/src/render.rs        |  3 +++
 eden/scm/lib/renderdag/src/test_fixtures.rs | 12 +++++++++
 5 files changed, 88 insertions(+)

diff --git a/eden/scm/lib/renderdag/src/ascii.rs b/eden/scm/lib/renderdag/src/ascii.rs
index b67f374644537..c32f894ed3124 100644
--- a/eden/scm/lib/renderdag/src/ascii.rs
+++ b/eden/scm/lib/renderdag/src/ascii.rs
@@ -240,6 +240,35 @@ mod tests {
         );
     }
 
+    #[test]
+    fn basic_disconnected() {
+        assert_eq!(
+            render(&test_fixtures::BASIC_DISCONNECTED),
+            r#"
+            o  C
+            |
+            o  B
+            
+            o  A"#
+        );
+    }
+
+    #[test]
+    fn basic_disconnected_min_row_height_1() {
+        let mut renderer = GraphRowRenderer::new()
+            .output()
+            .with_min_row_height(1)
+            .build_ascii();
+        assert_eq!(
+            render_string(&test_fixtures::BASIC_DISCONNECTED, &mut renderer),
+            r#"
+            o  C
+            |
+            o  B
+            o  A"#
+        );
+    }
+
     #[test]
     fn branches_and_merges() {
         assert_eq!(
diff --git a/eden/scm/lib/renderdag/src/ascii_large.rs b/eden/scm/lib/renderdag/src/ascii_large.rs
index 3baa80ff961e9..5848b710ea445 100644
--- a/eden/scm/lib/renderdag/src/ascii_large.rs
+++ b/eden/scm/lib/renderdag/src/ascii_large.rs
@@ -296,6 +296,21 @@ mod tests {
         );
     }
 
+    #[test]
+    fn basic_disconnected() {
+        assert_eq!(
+            render(&test_fixtures::BASIC_DISCONNECTED),
+            r#"
+            o  C
+            |
+            |
+            o  B
+            
+            
+            o  A"#
+        );
+    }
+
     #[test]
     fn branches_and_merges() {
         assert_eq!(
diff --git a/eden/scm/lib/renderdag/src/box_drawing.rs b/eden/scm/lib/renderdag/src/box_drawing.rs
index 2401b9a19d5c8..ad12db952cf14 100644
--- a/eden/scm/lib/renderdag/src/box_drawing.rs
+++ b/eden/scm/lib/renderdag/src/box_drawing.rs
@@ -319,6 +319,35 @@ mod tests {
         );
     }
 
+    #[test]
+    fn basic_disconnected() {
+        assert_eq!(
+            render(&test_fixtures::BASIC_DISCONNECTED),
+            r#"
+            o  C
+            │
+            o  B
+            
+            o  A"#
+        );
+    }
+
+    #[test]
+    fn basic_disconnected_min_row_height_1() {
+        let mut renderer = GraphRowRenderer::new()
+            .output()
+            .with_min_row_height(1)
+            .build_box_drawing();
+        assert_eq!(
+            render_string(&test_fixtures::BASIC_DISCONNECTED, &mut renderer),
+            r#"
+            o  C
+            │
+            o  B
+            o  A"#
+        );
+    }
+
     #[test]
     fn branches_and_merges() {
         assert_eq!(
diff --git a/eden/scm/lib/renderdag/src/render.rs b/eden/scm/lib/renderdag/src/render.rs
index 78081c652233e..599b3142f7fa7 100644
--- a/eden/scm/lib/renderdag/src/render.rs
+++ b/eden/scm/lib/renderdag/src/render.rs
@@ -518,6 +518,9 @@ where
                 } else if i == column {
                     link_line[i] |= LinkLine::CHILD
                         | p.to_link_line(LinkLine::VERT_PARENT, LinkLine::VERT_ANCESTOR);
+                    if p.id().is_some() {
+                        need_link_line = true;
+                    }
                 } else {
                     link_line[i] |=
                         p.to_link_line(LinkLine::LEFT_FORK_PARENT, LinkLine::LEFT_FORK_ANCESTOR);
diff --git a/eden/scm/lib/renderdag/src/test_fixtures.rs b/eden/scm/lib/renderdag/src/test_fixtures.rs
index 4678151108ffd..46e24f52029d5 100644
--- a/eden/scm/lib/renderdag/src/test_fixtures.rs
+++ b/eden/scm/lib/renderdag/src/test_fixtures.rs
@@ -23,6 +23,18 @@ pub(crate) const BASIC: TestFixture = TestFixture {
     missing: &[],
 };
 
+// A-B is a connected pair; C is an isolated node that ends up in the same
+// column after A's column is freed. Used to verify that the renderer
+// visually distinguishes connected from unconnected adjacent nodes.
+pub(crate) const BASIC_DISCONNECTED: TestFixture = TestFixture {
+    dag: "A B-C",
+    messages: &[],
+    heads: &["A", "C"],
+    reserve: &[],
+    ancestors: &[],
+    missing: &[],
+};
+
 pub(crate) const BRANCHES_AND_MERGES: TestFixture = TestFixture {
     dag: r#"
                       T /---------------N--O---\           T