Also use control pictures for pager prefix

The test case shows that the pager rendering is not quite right.  It renders
'{\', leaving out the newline.  This rendering is ambiguous.

Let's fix it by rendering \n as control picture, like we do for other control
characters in the pager.

src/pager.rs

@@ -8,13 +8,12 @@ use crate::common::{
 };
 use crate::complete::Completion;
 use crate::editable_line::EditableLine;
-use crate::fallback::{fish_wcswidth, fish_wcwidth};
 #[allow(unused_imports)]
 use crate::future::IsSomeAnd;
 use crate::highlight::{highlight_shell, HighlightRole, HighlightSpec};
 use crate::libc::MB_CUR_MAX;
 use crate::operation_context::OperationContext;
-use crate::screen::{Line, ScreenData};
+use crate::screen::{wcswidth_rendered, wcwidth_rendered, Line, ScreenData};
 use crate::termsize::Termsize;
 use crate::wchar::prelude::*;
 use crate::wcstringutil::string_fuzzy_match_string;
@@ -344,7 +343,7 @@ impl Pager {
     }
 
     fn measure_completion_infos(&mut self) {
-        let prefix_len = usize::try_from(fish_wcswidth(&self.prefix));
+        let prefix_len = wcswidth_rendered(&self.prefix);
         for comp in &mut self.unfiltered_completion_infos {
             let comp_strings = &mut comp.comp;
 
@@ -354,14 +353,14 @@ impl Pager {
                     comp.comp_width += 2;
                 }
 
-                // fish_wcswidth() can return -1 if it can't calculate the width. So be cautious.
+                // This can return -1 if it can't calculate the width. So be cautious.
-                let comp_width = fish_wcswidth(comp_string);
+                let comp_width = wcswidth_rendered(comp_string);
-                comp.comp_width += prefix_len.unwrap_or_default();
+                comp.comp_width += usize::try_from(prefix_len).unwrap_or_default();
                 comp.comp_width += usize::try_from(comp_width).unwrap_or_default();
             }
 
-            // fish_wcswidth() can return -1 if it can't calculate the width. So be cautious.
+            // This can return -1 if it can't calculate the width. So be cautious.
-            let desc_width = fish_wcswidth(&comp.desc);
+            let desc_width = wcswidth_rendered(&comp.desc);
             comp.desc_width = usize::try_from(desc_width).unwrap_or_default();
         }
     }
@@ -1071,7 +1070,7 @@ fn print_max_impl(
 ) -> usize {
     let mut remaining = max;
     for (i, c) in s.chars().enumerate() {
-        let iwidth_c = fish_wcwidth(c);
+        let iwidth_c = wcwidth_rendered(c);
         let Ok(width_c) = usize::try_from(iwidth_c) else {
             // skip non-printable characters
             continue;
@@ -1084,7 +1083,7 @@ fn print_max_impl(
         let ellipsis = get_ellipsis_char();
         if (width_c == remaining) && (has_more || i + 1 < s.len()) {
             line.append(ellipsis, color(i));
-            let ellipsis_width = fish_wcwidth(ellipsis);
+            let ellipsis_width = wcwidth_rendered(ellipsis);
             remaining = remaining.saturating_sub(usize::try_from(ellipsis_width).unwrap());
             break;
         }

src/screen.rs

@@ -103,7 +103,7 @@ impl Line {
     pub fn wcswidth_min_0(&self, max: usize /* = usize::MAX */) -> usize {
         let mut result: usize = 0;
         for c in &self.text[..max.min(self.text.len())] {
-            result += wcwidth_rendered(c.character);
+            result += wcwidth_rendered_min_0(c.character);
         }
         result
     }
@@ -327,7 +327,7 @@ impl Screen {
                 colors[i],
                 usize::try_from(indent[i]).unwrap(),
                 first_line_prompt_space,
-                wcwidth_rendered(effective_commandline.as_char_slice()[i]),
+                wcwidth_rendered_min_0(effective_commandline.as_char_slice()[i]),
             );
             i += 1;
         }
@@ -925,7 +925,7 @@ impl Screen {
             // Skip over skip_remaining width worth of characters.
             let mut j = 0;
             while j < o_line(&zelf, i).len() {
-                let width = wcwidth_rendered(o_line(&zelf, i).char_at(j));
+                let width = wcwidth_rendered_min_0(o_line(&zelf, i).char_at(j));
                 if skip_remaining < width {
                     break;
                 }
@@ -936,7 +936,7 @@ impl Screen {
 
             // Skip over zero-width characters (e.g. combining marks at the end of the prompt).
             while j < o_line(&zelf, i).len() {
-                let width = wcwidth_rendered(o_line(&zelf, i).char_at(j));
+                let width = wcwidth_rendered_min_0(o_line(&zelf, i).char_at(j));
                 if width > 0 {
                     break;
                 }
@@ -969,7 +969,7 @@ impl Screen {
                 let color = o_line(&zelf, i).color_at(j);
                 set_color(&mut zelf, color);
                 let ch = o_line(&zelf, i).char_at(j);
-                let width = wcwidth_rendered(ch);
+                let width = wcwidth_rendered_min_0(ch);
                 zelf.write_char(ch, isize::try_from(width).unwrap());
                 current_width += width;
                 j += 1;
@@ -1524,7 +1524,7 @@ fn measure_run_from(
             width = next_tab_stop(width);
         } else {
             // Ordinary char. Add its width with care to ignore control chars which have width -1.
-            width += wcwidth_rendered(input.char_at(idx));
+            width += wcwidth_rendered_min_0(input.char_at(idx));
         }
         idx += 1;
     }
@@ -1570,7 +1570,7 @@ fn truncate_run(
             curr_width = measure_run_from(run, 0, None, cache);
             idx = 0;
         } else {
-            let char_width = wcwidth_rendered(c);
+            let char_width = wcwidth_rendered_min_0(c);
             curr_width -= std::cmp::min(curr_width, char_width);
             run.remove(idx);
         }
@@ -1719,7 +1719,7 @@ fn compute_layout(
             multiline = true;
             break;
         } else {
-            first_line_width += wcwidth_rendered(c);
+            first_line_width += wcwidth_rendered_min_0(c);
         }
     }
     let first_command_line_width = first_line_width;
@@ -1734,7 +1734,7 @@ fn compute_layout(
         autosuggest_truncated_widths.reserve(1 + autosuggestion_str.len());
         for c in autosuggestion.chars() {
             autosuggest_truncated_widths.push(autosuggest_total_width);
-            autosuggest_total_width += wcwidth_rendered(c);
+            autosuggest_total_width += wcwidth_rendered_min_0(c);
         }
     }
 
@@ -1839,6 +1839,12 @@ fn rendered_character(c: char) -> char {
     }
 }
 
-fn wcwidth_rendered(c: char) -> usize {
+fn wcwidth_rendered_min_0(c: char) -> usize {
-    usize::try_from(fish_wcwidth(rendered_character(c))).unwrap_or_default()
+    usize::try_from(wcwidth_rendered(c)).unwrap()
+}
+pub fn wcwidth_rendered(c: char) -> isize {
+    fish_wcwidth(rendered_character(c))
+}
+pub fn wcswidth_rendered(s: &wstr) -> isize {
+    s.chars().map(|c| fish_wcwidth(rendered_character(c))).sum()
 }

src/tests/pager.rs

@@ -194,4 +194,15 @@ fn test_pager_layout() {
     validate!(&mut pager, 18, L!("abcdefghijklmnopq…"));
     validate!(&mut pager, 17, L!("abcdefghijklmnop…"));
     validate!(&mut pager, 16, L!("abcdefghijklmno…"));
+
+    // Newlines in prefix
+    let c4s = vec![Completion::new(
+        L!("Hello").to_owned(),
+        L!("").to_owned(),
+        StringFuzzyMatch::exact_match(),
+        CompleteFlags::default(),
+    )];
+    pager.set_prefix(L!("{\\\n"), false); // }
+    pager.set_completions(&c4s, true);
+    validate!(&mut pager, 30, L!("{\\␊Hello")); // }
 }