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};
 
@@ -144,6 +144,30 @@ impl<'a> Gap<'a> {
             prev_chunk,
         })
     }
+
+    fn contiguous_empty_lines(&self) -> Vec<Span> {
+        let mut spans = Vec::new();
+
+        let mut prev_span = *self.empty_lines.first().expect("at least one empty line");
+
+        // The BytePos subtraction here is safe, as before an empty line, there must be at least one
+        // attribute/comment.
+        prev_span = prev_span.with_lo(prev_span.lo() - BytePos(1));
+        for empty_line in self.empty_lines.iter().skip(1) {
+            if empty_line.lo() - prev_span.hi() > BytePos(1) {
+                // If the empty line doesn't immidiately follow the previous one, push the previous span...
+                spans.push(prev_span);
+                // ...and start a new one
+                prev_span = empty_line.with_lo(empty_line.lo() - BytePos(1));
+            } else {
+                // Otherwise, extend the previous span
+                prev_span = prev_span.with_hi(empty_line.hi());
+            }
+        }
+        spans.push(prev_span);
+
+        spans
+    }
 }
 
 /// If the node the attributes/docs apply to is the first in the module/crate suggest converting
@@ -192,6 +216,7 @@ 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().flat_map(|gap| gap.contiguous_empty_lines());
     let mut has_comment = false;
     let mut has_attr = false;
     for gap in gaps {
@@ -227,7 +252,9 @@ 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,
             );

tests/ui/empty_line_after/outer_attribute.1.fixed

@@ -51,6 +51,11 @@ mod foo {}
 // Still lint cases where the empty line does not immediately follow the attribute
 fn comment_before_empty_line() {}
 
+//~v empty_line_after_outer_attr
+#[allow(unused)]
+// This comment is isolated
+pub fn isolated_comment() {}
+
 #[doc = "
 Returns the escaped value of the textual representation of
 

tests/ui/empty_line_after/outer_attribute.2.fixed

@@ -54,6 +54,11 @@ mod foo {}
 // Still lint cases where the empty line does not immediately follow the attribute
 fn comment_before_empty_line() {}
 
+//~v empty_line_after_outer_attr
+#[allow(unused)]
+// This comment is isolated
+pub fn isolated_comment() {}
+
 #[doc = "
 Returns the escaped value of the textual representation of
 

tests/ui/empty_line_after/outer_attribute.rs

@@ -60,6 +60,13 @@ mod foo {}
 
 fn comment_before_empty_line() {}
 
+//~v empty_line_after_outer_attr
+#[allow(unused)]
+
+// This comment is isolated
+
+pub fn isolated_comment() {}
+
 #[doc = "
 Returns the escaped value of the textual representation of
 

tests/ui/empty_line_after/outer_attribute.stderr

@@ -99,5 +99,18 @@ LL |   fn comment_before_empty_line() {}
    |
    = help: if the empty line is unintentional remove it
 
-error: aborting due to 8 previous errors
+error: empty lines after outer attribute
+  --> tests/ui/empty_line_after/outer_attribute.rs:64:1
+   |
+LL | / #[allow(unused)]
+LL | |
+LL | | // This comment is isolated
+LL | |
+   | |_
+LL |   pub fn isolated_comment() {}
+   |   ------------------------- the attribute applies to this function
+   |
+   = help: if the empty lines are unintentional remove them
+
+error: aborting due to 9 previous errors