Use contiguous spans for empty_line_after_* suggestion

Replacing an empty span (which an empty line is) with an empty string triggers a
debug assertion in rustc. This fixes the debug assertion by using contiguous
spans, with the same resulting suggestion.

Author: flip1995

clippy_lints/src/doc/empty_line_after.rs

@@ -8,7 +8,7 @@ use rustc_errors::{Applicability, Diag, SuggestionStyle};
 use rustc_hir::{ItemKind, Node};
 use rustc_lexer::TokenKind;
 use rustc_lint::LateContext;
-use rustc_span::{ExpnKind, InnerSpan, Span, SpanData};
+use rustc_span::{BytePos, ExpnKind, InnerSpan, Span, SpanData};
 
 use super::{EMPTY_LINE_AFTER_DOC_COMMENTS, EMPTY_LINE_AFTER_OUTER_ATTR};
 
@@ -192,6 +192,16 @@ fn check_gaps(cx: &LateContext<'_>, gaps: &[Gap<'_>]) -> bool {
         return false;
     };
     let empty_lines = || gaps.iter().flat_map(|gap| gap.empty_lines.iter().copied());
+    let contiguous_empty_lines = || {
+        gaps.iter().map(|gap| {
+            let first_line = gap.empty_lines.first().unwrap();
+            let last_line = gap.empty_lines.last().unwrap();
+
+            // The BytePos subtraction here is save, as before an empty line, there must be at least one
+            // attribute/doc comment.
+            last_line.with_lo(first_line.lo() - BytePos(1))
+        })
+    };
     let mut has_comment = false;
     let mut has_attr = false;
     for gap in gaps {
@@ -230,7 +240,9 @@ fn check_gaps(cx: &LateContext<'_>, gaps: &[Gap<'_>]) -> bool {
 
             diag.multipart_suggestion_with_style(
                 format!("if the empty {lines} {are} unintentional remove {them}"),
-                empty_lines().map(|empty_line| (empty_line, String::new())).collect(),
+                contiguous_empty_lines()
+                    .map(|empty_lines| (empty_lines, String::new()))
+                    .collect(),
                 Applicability::MaybeIncorrect,
                 SuggestionStyle::HideCodeAlways,
             );