Rollup merge of #134181 - estebank:trim-render, r=oli-obk

Tweak multispan rendering to reduce output length

Consider comments and bare delimiters the same as an "empty line" for purposes of hiding rendered code output of long multispans. This results in more aggressive shortening of rendered output without losing too much context, specially in `*.stderr` tests that have "hidden" comments. We do that check not only on the first 4 lines of the multispan, but now also on the previous to last line as well.

1 files changed, 12 insertions, 3 deletions

diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 1b6c6edcc61..ac2f91cdeb3 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -3048,11 +3048,19 @@ impl FileWithAnnotatedLines {
                 // working correctly.
                 let middle = min(ann.line_start + 4, ann.line_end);
                 // We'll show up to 4 lines past the beginning of the multispan start.
-                // We will *not* include the tail of lines that are only whitespace.
+                // We will *not* include the tail of lines that are only whitespace, a comment or
+                // a bare delimiter.
+                let filter = |s: &str| {
+                    let s = s.trim();
+                    // Consider comments as empty, but don't consider docstrings to be empty.
+                    !(s.starts_with("//") && !(s.starts_with("///") || s.starts_with("//!")))
+                        // Consider lines with nothing but whitespace, a single delimiter as empty.
+                        && !["", "{", "}", "(", ")", "[", "]"].contains(&s)
+                };
                 let until = (ann.line_start..middle)
                     .rev()
                     .filter_map(|line| file.get_line(line - 1).map(|s| (line + 1, s)))
-                    .find(|(_, s)| !s.trim().is_empty())
+                    .find(|(_, s)| filter(s))
                     .map(|(line, _)| line)
                     .unwrap_or(ann.line_start);
                 for line in ann.line_start + 1..until {
@@ -3060,7 +3068,8 @@ impl FileWithAnnotatedLines {
                     add_annotation_to_file(&mut output, Lrc::clone(&file), line, ann.as_line());
                 }
                 let line_end = ann.line_end - 1;
-                if middle < line_end {
+                let end_is_empty = file.get_line(line_end - 1).map_or(false, |s| !filter(&s));
+                if middle < line_end && !end_is_empty {
                     add_annotation_to_file(&mut output, Lrc::clone(&file), line_end, ann.as_line());
                 }
             } else {