ruff_annotate_snippets: fix false positive line trimming

This fix was sent upstream and the PR description includes more details:
rust-lang/annotate-snippets-rs#170

Without this fix, there was an errant snapshot diff that looked like
this:

  |
1 |   version = "0.1.0"
2 |   # Ensure that the spans from toml handle utf-8 correctly
3 |   authors = [
  |  ___________^
4 | |     { name = "Z...ALGO", email = 1 }
5 | | ]
  | |_^ RUF200
  |

That ellipsis should _not_ be inserted since the line is not actually
truncated. The handling of line length (in bytes versus actual rendered
length) wasn't quite being handled correctly in all cases.

With this fix, there's (correctly) no snapshot diff.

Author: BurntSushi

crates/ruff_annotate_snippets/src/renderer/display_list.rs

@@ -331,28 +331,27 @@ impl DisplaySet<'_> {
 
                     // On long lines, we strip the source line, accounting for unicode.
                     let mut taken = 0;
-                    let code: String = text
-                        .chars()
-                        .skip(left)
-                        .take_while(|ch| {
-                            // Make sure that the trimming on the right will fall within the terminal width.
-                            // FIXME: `unicode_width` sometimes disagrees with terminals on how wide a `char`
-                            // is. For now, just accept that sometimes the code line will be longer than
-                            // desired.
-                            let next = unicode_width::UnicodeWidthChar::width(*ch).unwrap_or(1);
-                            if taken + next > right - left {
-                                return false;
-                            }
-                            taken += next;
-                            true
-                        })
-                        .collect();
+                    let mut was_cut_right = false;
+                    let mut code = String::new();
+                    for ch in text.chars().skip(left) {
+                        // Make sure that the trimming on the right will fall within the terminal width.
+                        // FIXME: `unicode_width` sometimes disagrees with terminals on how wide a `char`
+                        // is. For now, just accept that sometimes the code line will be longer than
+                        // desired.
+                        let next = unicode_width::UnicodeWidthChar::width(ch).unwrap_or(1);
+                        if taken + next > right - left {
+                            was_cut_right = true;
+                            break;
+                        }
+                        taken += next;
+                        code.push(ch);
+                    }
                     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);
                     }
-                    if self.margin.was_cut_right(line_len) {
+                    if was_cut_right {
                         buffer.puts(line_offset, code_offset + taken - 3, "...", *lineno_color);
                     }
 

crates/ruff_annotate_snippets/src/renderer/margin.rs

@@ -58,18 +58,6 @@ impl Margin {
         self.computed_left > 0
     }
 
-    pub(crate) fn was_cut_right(&self, line_len: usize) -> bool {
-        let right =
-            if self.computed_right == self.span_right || self.computed_right == self.label_right {
-                // Account for the "..." padding given above. Otherwise we end up with code lines that
-                // do fit but end in "..." as if they were trimmed.
-                self.computed_right - ELLIPSIS_PASSING
-            } else {
-                self.computed_right
-            };
-        right < line_len && self.computed_left + self.term_width < line_len
-    }
-
     fn compute(&mut self, max_line_len: usize) {
         // When there's a lot of whitespace (>20), we want to trim it as it is useless.
         self.computed_left = if self.whitespace_left > LONG_WHITESPACE {