ruff_annotate_snippets: support overriding the "cut indicator"

We do this because `...` is valid Python, which makes it pretty likely
that some line trimming will lead to ambiguous output. So we add support
for overriding the cut indicator. This also requires changing some of
the alignment math, which was previously tightly coupled to `...`.

For Ruff, we go with `…` (`U+2026 HORIZONTAL ELLIPSIS`) for our cut
indicator.

For more details, see the patch sent to upstream:
https://github.com/rust-lang/annotate-snippets-rs/pull/172

crates/ruff_annotate_snippets/src/renderer/display_list.rs

@@ -38,6 +38,8 @@ use std::fmt::Display;
 use std::ops::Range;
 use std::{cmp, fmt};
 
+use unicode_width::UnicodeWidthStr;
+
 use crate::renderer::styled_buffer::StyledBuffer;
 use crate::renderer::{stylesheet::Stylesheet, Margin, Style, DEFAULT_TERM_WIDTH};
 
@@ -53,6 +55,7 @@ pub(crate) struct DisplayList<'a> {
     pub(crate) body: Vec<DisplaySet<'a>>,
     pub(crate) stylesheet: &'a Stylesheet,
     pub(crate) anonymized_line_numbers: bool,
+    pub(crate) cut_indicator: &'static str,
 }
 
 impl PartialEq for DisplayList<'_> {
@@ -119,13 +122,21 @@ impl<'a> DisplayList<'a> {
         stylesheet: &'a Stylesheet,
         anonymized_line_numbers: bool,
         term_width: usize,
+        cut_indicator: &'static str,
     ) -> DisplayList<'a> {
-        let body = format_message(message, term_width, anonymized_line_numbers, true);
+        let body = format_message(
+            message,
+            term_width,
+            anonymized_line_numbers,
+            cut_indicator,
+            true,
+        );
 
         Self {
             body,
             stylesheet,
             anonymized_line_numbers,
+            cut_indicator,
         }
     }
 
@@ -143,6 +154,7 @@ impl<'a> DisplayList<'a> {
                 multiline_depth,
                 self.stylesheet,
                 self.anonymized_line_numbers,
+                self.cut_indicator,
                 buffer,
             )?;
         }
@@ -270,6 +282,7 @@ impl DisplaySet<'_> {
     }
 
     // Adapted from https://github.com/rust-lang/rust/blob/d371d17496f2ce3a56da76aa083f4ef157572c20/compiler/rustc_errors/src/emitter.rs#L706-L1211
+    #[allow(clippy::too_many_arguments)]
     #[inline]
     fn format_line(
         &self,
@@ -278,6 +291,7 @@ impl DisplaySet<'_> {
         multiline_depth: usize,
         stylesheet: &Stylesheet,
         anonymized_line_numbers: bool,
+        cut_indicator: &'static str,
         buffer: &mut StyledBuffer,
     ) -> fmt::Result {
         let line_offset = buffer.num_lines();
@@ -349,10 +363,15 @@ impl DisplaySet<'_> {
                     buffer.puts(line_offset, code_offset, &code, Style::new());
                     if self.margin.was_cut_left() {
                         // We have stripped some code/whitespace from the beginning, make it clear.
-                        buffer.puts(line_offset, code_offset, "...", *lineno_color);
+                        buffer.puts(line_offset, code_offset, cut_indicator, *lineno_color);
                     }
                     if was_cut_right {
-                        buffer.puts(line_offset, code_offset + taken - 3, "...", *lineno_color);
+                        buffer.puts(
+                            line_offset,
+                            code_offset + taken - cut_indicator.width(),
+                            cut_indicator,
+                            *lineno_color,
+                        );
                     }
 
                     let left: usize = text
@@ -724,7 +743,7 @@ impl DisplaySet<'_> {
                 Ok(())
             }
             DisplayLine::Fold { inline_marks } => {
-                buffer.puts(line_offset, 0, "...", *stylesheet.line_no());
+                buffer.puts(line_offset, 0, cut_indicator, *stylesheet.line_no());
                 if !inline_marks.is_empty() || 0 < multiline_depth {
                     format_inline_marks(
                         line_offset,
@@ -987,12 +1006,13 @@ impl<'a> Iterator for CursorLines<'a> {
     }
 }
 
-fn format_message(
-    message: snippet::Message<'_>,
+fn format_message<'m>(
+    message: snippet::Message<'m>,
     term_width: usize,
     anonymized_line_numbers: bool,
+    cut_indicator: &'static str,
     primary: bool,
-) -> Vec<DisplaySet<'_>> {
+) -> Vec<DisplaySet<'m>> {
     let snippet::Message {
         level,
         id,
@@ -1016,6 +1036,7 @@ fn format_message(
             !footer.is_empty(),
             term_width,
             anonymized_line_numbers,
+            cut_indicator,
         ));
     }
 
@@ -1035,6 +1056,7 @@ fn format_message(
             annotation,
             term_width,
             anonymized_line_numbers,
+            cut_indicator,
             false,
         ));
     }
@@ -1089,13 +1111,14 @@ fn format_label(
     result
 }
 
-fn format_snippet(
-    snippet: snippet::Snippet<'_>,
+fn format_snippet<'m>(
+    snippet: snippet::Snippet<'m>,
     is_first: bool,
     has_footer: bool,
     term_width: usize,
     anonymized_line_numbers: bool,
-) -> DisplaySet<'_> {
+    cut_indicator: &'static str,
+) -> DisplaySet<'m> {
     let main_range = snippet.annotations.first().map(|x| x.range.start);
     let origin = snippet.origin;
     let need_empty_header = origin.is_some() || is_first;
@@ -1105,6 +1128,7 @@ fn format_snippet(
         has_footer,
         term_width,
         anonymized_line_numbers,
+        cut_indicator,
     );
     let header = format_header(origin, main_range, &body.display_lines, is_first);
 
@@ -1241,7 +1265,7 @@ fn fold_body(body: Vec<DisplayLine<'_>>) -> Vec<DisplayLine<'_>> {
                     match unhighlighed_lines.len() {
                         0 => {}
                         n if n <= INNER_UNFOLD_SIZE => {
-                            // Rather than render `...`, don't fold
+                            // Rather than render our cut indicator, don't fold
                             lines.append(&mut unhighlighed_lines);
                         }
                         _ => {
@@ -1280,13 +1304,14 @@ fn fold_body(body: Vec<DisplayLine<'_>>) -> Vec<DisplayLine<'_>> {
     lines
 }
 
-fn format_body(
-    snippet: snippet::Snippet<'_>,
+fn format_body<'m>(
+    snippet: snippet::Snippet<'m>,
     need_empty_header: bool,
     has_footer: bool,
     term_width: usize,
     anonymized_line_numbers: bool,
-) -> DisplaySet<'_> {
+    cut_indicator: &'static str,
+) -> DisplaySet<'m> {
     let source_len = snippet.source.len();
     if let Some(bigger) = snippet.annotations.iter().find_map(|x| {
         // Allow highlighting one past the last character in the source.
@@ -1617,7 +1642,7 @@ fn format_body(
         current_line.to_string().len()
     };
 
-    let width_offset = 3 + max_line_num_len;
+    let width_offset = cut_indicator.len() + max_line_num_len;
 
     if span_left_margin == usize::MAX {
         span_left_margin = 0;

crates/ruff_annotate_snippets/src/renderer/mod.rs

@@ -9,6 +9,7 @@
 //!
 //!  let renderer = Renderer::styled();
 //!  println!("{}", renderer.render(snippet));
+//! ```
 
 mod display_list;
 mod margin;
@@ -30,6 +31,7 @@ pub struct Renderer {
     anonymized_line_numbers: bool,
     term_width: usize,
     stylesheet: Stylesheet,
+    cut_indicator: &'static str,
 }
 
 impl Renderer {
@@ -39,6 +41,7 @@ impl Renderer {
             anonymized_line_numbers: false,
             term_width: DEFAULT_TERM_WIDTH,
             stylesheet: Stylesheet::plain(),
+            cut_indicator: "...",
         }
     }
 
@@ -151,6 +154,14 @@ impl Renderer {
         self
     }
 
+    /// Set the string used for when a long line is cut.
+    ///
+    /// The default is `...` (three `U+002E` characters).
+    pub const fn cut_indicator(mut self, string: &'static str) -> Self {
+        self.cut_indicator = string;
+        self
+    }
+
     /// Render a snippet into a `Display`able object
     pub fn render<'a>(&'a self, msg: Message<'a>) -> impl Display + 'a {
         DisplayList::new(
@@ -158,6 +169,7 @@ impl Renderer {
             &self.stylesheet,
             self.anonymized_line_numbers,
             self.term_width,
+            self.cut_indicator,
         )
     }
 }

crates/ruff_annotate_snippets/tests/formatter.rs

@@ -990,3 +990,42 @@ error: title
     let renderer = Renderer::plain();
     assert_data_eq!(renderer.render(input).to_string(), expected);
 }
+
+#[test]
+fn long_line_cut() {
+    let source = "abcd abcd abcd abcd abcd abcd abcd";
+    let input = Level::Error.title("").snippet(
+        Snippet::source(source)
+            .line_start(1)
+            .annotation(Level::Error.span(0..4)),
+    );
+    let expected = str![[r#"
+error
+  |
+1 | abcd abcd a...
+  | ^^^^
+  |
+"#]];
+    let renderer = Renderer::plain().term_width(18);
+    assert_data_eq!(renderer.render(input).to_string(), expected);
+}
+
+#[test]
+fn long_line_cut_custom() {
+    let source = "abcd abcd abcd abcd abcd abcd abcd";
+    let input = Level::Error.title("").snippet(
+        Snippet::source(source)
+            .line_start(1)
+            .annotation(Level::Error.span(0..4)),
+    );
+    // This trims a little less because `…` is visually smaller than `...`.
+    let expected = str![[r#"
+error
+  |
+1 | abcd abcd abc…
+  | ^^^^
+  |
+"#]];
+    let renderer = Renderer::plain().term_width(18).cut_indicator("…");
+    assert_data_eq!(renderer.render(input).to_string(), expected);
+}