Fix bad layout computation with right prompt

Commit 1c4e5cadf2 (Autosuggestions in multi-line
command lines, 2024-12-15) accidentally passed an empty
"commandline_before_suggestion" to compute_layout() when there is
no autosuggestion.

Closes #10996

src/reader.rs

@@ -1545,7 +1545,7 @@ impl<'a> Reader<'a> {
                 Cow::Owned(
                     wstr::from_char_slice(&[get_obfuscation_read_char()]).repeat(cmd_line.len()),
                 ),
-                0..0,
+                None,
             )
         } else if self.is_at_line_with_autosuggestion() {
             // Combine the command and autosuggestion into one string.
@@ -1559,11 +1559,12 @@ impl<'a> Reader<'a> {
                     autosuggestion.search_string_range.clone(),
                     &autosuggestion.text,
                 )),
-                autosuggested_start..autosuggested_end,
+                Some(autosuggested_start..autosuggested_end),
             )
         } else {
-            (Cow::Borrowed(cmd_line.text()), 0..0)
+            (Cow::Borrowed(cmd_line.text()), None)
         };
+        let autosuggested_range = autosuggested_range.unwrap_or(full_line.len()..full_line.len());
 
         // Copy the colors and insert the autosuggestion color.
         let data = &self.data.rendered_layout;

tests/checks/tmux-commandline.fish

@@ -11,7 +11,7 @@ tmux-sleep
 isolated-tmux capture-pane -p
 # CHECK: prompt 1> echo foobar|cat
 
-isolated-tmux send-keys C-k C-u C-l 'commandline -i (seq $LINES) scroll_here' Enter
+isolated-tmux send-keys C-k C-u C-l 'commandline -i "\'$(seq $LINES)" scroll_here' Enter
 tmux-sleep
 isolated-tmux capture-pane -p
 # CHECK: 2
@@ -24,3 +24,19 @@ isolated-tmux capture-pane -p
 # CHECK: 9
 # CHECK: 10
 # CHECK: scroll_here
+
+# Soft-wrapped commandline with omitted right prompt.
+isolated-tmux send-keys C-c
+tmux-sleep
+isolated-tmux send-keys C-l '
+    function fish_right_prompt
+        echo right-prompt
+    end
+    commandline -i "echo $(printf %0"$COLUMNS"d)"
+' Enter
+tmux-sleep
+isolated-tmux capture-pane -p | sed 1,5d
+# CHECK: prompt 4> echo 00000000000000000000000000000000000000000000000000000000000000000
+# CHECK: 000000000000000
+# CHECK: 00000000000000000000000000000000000000000000000000000000000000000000000000000000
+# CHECK: prompt 5>                                                           right-prompt