Clean up and comment EmitterWriter.draw_code_line

1 files changed, 32 insertions, 59 deletions

diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 61e1155a79f..9768526a2f4 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -1882,9 +1882,8 @@ impl EmitterWriter {
                             &mut buffer,
                             &mut row_num,
                             &Vec::new(),
-                            p,
+                            p + line_start,
                             l,
-                            line_start,
                             show_code_change,
                             max_line_num_len,
                             &file_lines,
@@ -1907,9 +1906,8 @@ impl EmitterWriter {
                                 &mut buffer,
                                 &mut row_num,
                                 &Vec::new(),
-                                p,
+                                p + line_start,
                                 l,
-                                line_start,
                                 show_code_change,
                                 max_line_num_len,
                                 &file_lines,
@@ -1925,9 +1923,8 @@ impl EmitterWriter {
                                 &mut buffer,
                                 &mut row_num,
                                 &Vec::new(),
-                                p,
+                                p + line_start,
                                 l,
-                                line_start,
                                 show_code_change,
                                 max_line_num_len,
                                 &file_lines,
@@ -1941,9 +1938,8 @@ impl EmitterWriter {
                     &mut buffer,
                     &mut row_num,
                     highlight_parts,
-                    line_pos,
+                    line_pos + line_start,
                     line,
-                    line_start,
                     show_code_change,
                     max_line_num_len,
                     &file_lines,
@@ -2167,49 +2163,44 @@ impl EmitterWriter {
         buffer: &mut StyledBuffer,
         row_num: &mut usize,
         highlight_parts: &Vec<SubstitutionHighlight>,
-        line_pos: usize,
-        line: &str,
-        line_start: usize,
+        line_num: usize,
+        line_to_add: &str,
         show_code_change: DisplaySuggestion,
         max_line_num_len: usize,
         file_lines: &FileLines,
         is_multiline: bool,
     ) {
         if let DisplaySuggestion::Diff = show_code_change {
-            // Add the line number for both addition and removal to drive the point home.
-            //
-            // N - fn foo<A: T>(bar: A) {
-            // N + fn foo(bar: impl T) {
-            let number_of_lines = file_lines.lines.len();
-            for (index, line_to_remove) in
-                file_lines.lines.iter().take(number_of_lines - 1).enumerate()
-            {
+            // We need to print more than one line if the span we need to remove is multiline.
+            // For more info: https://github.com/rust-lang/rust/issues/92741
+            let lines_to_remove = file_lines.lines.iter().take(file_lines.lines.len() - 1);
+            for (index, line_to_remove) in lines_to_remove.enumerate() {
                 buffer.puts(
                     *row_num - 1,
                     0,
-                    &self.maybe_anonymized(line_start + line_pos + index),
+                    &self.maybe_anonymized(line_num + index),
                     Style::LineNumber,
                 );
                 buffer.puts(*row_num - 1, max_line_num_len + 1, "- ", Style::Removal);
-                buffer.puts(
-                    *row_num - 1,
-                    max_line_num_len + 3,
-                    &normalize_whitespace(
-                        &file_lines.file.get_line(line_to_remove.line_index).unwrap(),
-                    ),
-                    Style::NoStyle,
+                let line = normalize_whitespace(
+                    &file_lines.file.get_line(line_to_remove.line_index).unwrap(),
                 );
+                buffer.puts(*row_num - 1, max_line_num_len + 3, &line, Style::NoStyle);
                 *row_num += 1;
             }
-            let last_line = &file_lines
-                .file
-                .get_line(file_lines.lines[number_of_lines - 1].line_index)
-                .unwrap();
-            if last_line != line {
+            // If the last line is exactly equal to the line we need to add, we can skip both of them.
+            // This allows us to avoid output like the following:
+            // 2 - &
+            // 2 + if true { true } else { false }
+            // 3 - if true { true } else { false }
+            // If those lines aren't equal, we print their diff
+            let last_line_index = file_lines.lines[file_lines.lines.len() - 1].line_index;
+            let last_line = &file_lines.file.get_line(last_line_index).unwrap();
+            if last_line != line_to_add {
                 buffer.puts(
                     *row_num - 1,
                     0,
-                    &self.maybe_anonymized(line_start + line_pos + number_of_lines - 1),
+                    &self.maybe_anonymized(line_num + file_lines.lines.len() - 1),
                     Style::LineNumber,
                 );
                 buffer.puts(*row_num - 1, max_line_num_len + 1, "- ", Style::Removal);
@@ -2219,27 +2210,16 @@ impl EmitterWriter {
                     &normalize_whitespace(last_line),
                     Style::NoStyle,
                 );
-                buffer.puts(
-                    *row_num,
-                    0,
-                    &self.maybe_anonymized(line_start + line_pos),
-                    Style::LineNumber,
-                );
+                buffer.puts(*row_num, 0, &self.maybe_anonymized(line_num), Style::LineNumber);
                 buffer.puts(*row_num, max_line_num_len + 1, "+ ", Style::Addition);
-                // print the suggestion
-                buffer.append(*row_num, &normalize_whitespace(line), Style::NoStyle);
+                buffer.append(*row_num, &normalize_whitespace(line_to_add), Style::NoStyle);
             } else {
                 *row_num -= 2;
             }
         } else if is_multiline {
-            buffer.puts(
-                *row_num,
-                0,
-                &self.maybe_anonymized(line_start + line_pos),
-                Style::LineNumber,
-            );
+            buffer.puts(*row_num, 0, &self.maybe_anonymized(line_num), Style::LineNumber);
             match &highlight_parts[..] {
-                [SubstitutionHighlight { start: 0, end }] if *end == line.len() => {
+                [SubstitutionHighlight { start: 0, end }] if *end == line_to_add.len() => {
                     buffer.puts(*row_num, max_line_num_len + 1, "+ ", Style::Addition);
                 }
                 [] => {
@@ -2249,24 +2229,17 @@ impl EmitterWriter {
                     buffer.puts(*row_num, max_line_num_len + 1, "~ ", Style::Addition);
                 }
             }
-            // print the suggestion
-            buffer.append(*row_num, &normalize_whitespace(line), Style::NoStyle);
+            buffer.append(*row_num, &normalize_whitespace(line_to_add), Style::NoStyle);
         } else {
-            buffer.puts(
-                *row_num,
-                0,
-                &self.maybe_anonymized(line_start + line_pos),
-                Style::LineNumber,
-            );
+            buffer.puts(*row_num, 0, &self.maybe_anonymized(line_num), Style::LineNumber);
             draw_col_separator(buffer, *row_num, max_line_num_len + 1);
-            // print the suggestion
-            buffer.append(*row_num, &normalize_whitespace(line), Style::NoStyle);
+            buffer.append(*row_num, &normalize_whitespace(line_to_add), Style::NoStyle);
         }
 
         // Colorize addition/replacements with green.
         for &SubstitutionHighlight { start, end } in highlight_parts {
             // Account for tabs when highlighting (#87972).
-            let tabs: usize = line
+            let tabs: usize = line_to_add
                 .chars()
                 .take(start)
                 .map(|ch| match ch {