Fix underline interruption with empty cells

Since completely empty cells are not reported by the renderable cells
iterator, the line renderer has incorrectly assumed that these cells did
not cause any change in cell state, leading to underlines spanning empty
cells.

Instead of assuming that the line state is unchanged, the line
calculation now correctly interprets a jump in the renderable cells
column as an interruption of the line.

This fixes #1960.

1 files changed, 17 insertions, 13 deletions

diff --git a/src/renderer/lines.rs b/src/renderer/lines.rs
index 130ffdda..99d1f28f 100644
--- a/src/renderer/lines.rs
+++ b/src/renderer/lines.rs
@@ -13,11 +13,11 @@
 // limitations under the License.
 use std::collections::HashMap;
 
-use crate::term::{ SizeInfo, RenderableCell};
-use crate::term::cell::Flags;
 use crate::renderer::Rect;
-use font::Metrics;
+use crate::term::cell::Flags;
+use crate::term::{RenderableCell, SizeInfo};
 use crate::Rgb;
+use font::Metrics;
 
 /// Lines for underline and strikeout.
 pub struct Lines<'a> {
@@ -70,20 +70,24 @@ impl<'a> Lines<'a> {
             *start_cell = match *start_cell {
                 // Check for end if line is present
                 Some(ref mut start) => {
+                    let last_cell = self.last_cell.unwrap();
+
                     // No change in line
-                    if cell.line == start.line && cell.flags.contains(flag) && cell.fg == start.fg {
+                    if cell.line == start.line
+                        && cell.flags.contains(flag)
+                        && cell.fg == start.fg
+                        && cell.column == last_cell.column + 1
+                    {
                         continue;
                     }
 
-                    self.inner.push(
-                        create_rect(
-                            &start,
-                            &self.last_cell.unwrap(),
-                            flag,
-                            &self.metrics,
-                            &self.size,
-                        )
-                    );
+                    self.inner.push(create_rect(
+                        &start,
+                        &last_cell,
+                        flag,
+                        &self.metrics,
+                        &self.size,
+                    ));
 
                     // Start a new line if the flag is present
                     if cell.flags.contains(flag) {