When displaying multispans, ignore empty lines adjacent to ...

```
error[E0308]: `match` arms have incompatible types
   --> tests/ui/codemap_tests/huge_multispan_highlight.rs:98:18
    |
6   |       let _ = match true {
    |               ---------- `match` arms have incompatible types
7   |           true => (
    |  _________________-
8   | |             // last line shown in multispan header
...   |
96  | |
97  | |         ),
    | |_________- this is found to be of type `()`
98  |           false => "
    |  __________________^
...   |
119 | |
120 | |         ",
    | |_________^ expected `()`, found `&str`

error[E0308]: `match` arms have incompatible types
   --> tests/ui/codemap_tests/huge_multispan_highlight.rs:215:18
    |
122 |       let _ = match true {
    |               ---------- `match` arms have incompatible types
123 |           true => (
    |  _________________-
124 | |
125 | |         1 // last line shown in multispan header
...   |
213 | |
214 | |         ),
    | |_________- this is found to be of type `{integer}`
215 |           false => "
    |  __________________^
216 | |
217 | |
218 | |         1 last line shown in multispan
...   |
237 | |
238 | |         ",
    | |_________^ expected integer, found `&str`
```

Author: estebank

compiler/rustc_errors/src/emitter.rs

@@ -1638,6 +1638,27 @@ impl HumanEmitter {
                                     *style,
                                 );
                             }
+                            if let Some(line) = annotated_file.lines.get(line_idx) {
+                                for ann in &line.annotations {
+                                    if let AnnotationType::MultilineStart(pos) = ann.annotation_type
+                                    {
+                                        // In the case where we have elided the entire start of the
+                                        // multispan because those lines were empty, we still need
+                                        // to draw the `|`s across the `...`.
+                                        draw_multiline_line(
+                                            &mut buffer,
+                                            last_buffer_line_num,
+                                            width_offset,
+                                            pos,
+                                            if ann.is_primary {
+                                                Style::UnderlinePrimary
+                                            } else {
+                                                Style::UnderlineSecondary
+                                            },
+                                        );
+                                    }
+                                }
+                            }
                         } else if line_idx_delta == 2 {
                             let unannotated_line = annotated_file
                                 .file
@@ -1665,6 +1686,24 @@ impl HumanEmitter {
                                     *style,
                                 );
                             }
+                            if let Some(line) = annotated_file.lines.get(line_idx) {
+                                for ann in &line.annotations {
+                                    if let AnnotationType::MultilineStart(pos) = ann.annotation_type
+                                    {
+                                        draw_multiline_line(
+                                            &mut buffer,
+                                            last_buffer_line_num,
+                                            width_offset,
+                                            pos,
+                                            if ann.is_primary {
+                                                Style::UnderlinePrimary
+                                            } else {
+                                                Style::UnderlineSecondary
+                                            },
+                                        );
+                                    }
+                                }
+                            }
                         }
                     }
 
@@ -2417,7 +2456,15 @@ impl FileWithAnnotatedLines {
                 // the beginning doesn't have an underline, but the current logic seems to be
                 // working correctly.
                 let middle = min(ann.line_start + 4, ann.line_end);
-                for line in ann.line_start + 1..middle {
+                // 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.
+                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())
+                    .map(|(line, _)| line)
+                    .unwrap_or(ann.line_start);
+                for line in ann.line_start + 1..until {
                     // Every `|` that joins the beginning of the span (`___^`) to the end (`|__^`).
                     add_annotation_to_file(&mut output, file.clone(), line, ann.as_line());
                 }

compiler/rustc_expand/src/tests.rs

@@ -276,8 +276,7 @@ error: foo
   |
 2 |   fn foo() {
   |  __________^
-3 | |
-4 | |
+... |
 5 | |   }
   | |___^ test
 

src/tools/clippy/tests/ui/async_yields_async.stderr

@@ -81,8 +81,7 @@ LL |       let _m = async || {
    |  _______________________-
 LL | |         println!("I'm bored");
 LL | |         // Some more stuff
-LL | |
-LL | |         // Finally something to await
+...  |
 LL | |         CustomFutureType
    | |         ^^^^^^^^^^^^^^^^
    | |         |

src/tools/clippy/tests/ui/empty_line_after_outer_attribute.stderr

@@ -22,8 +22,7 @@ error: found an empty line after an outer attribute. Perhaps you forgot to add a
   --> tests/ui/empty_line_after_outer_attribute.rs:28:1
    |
 LL | / #[crate_type = "lib"]
-LL | |
-LL | |
+...  |
 LL | | fn with_two_newlines() { assert!(true) }
    | |_
 

tests/rustdoc-ui/lints/check.stderr

@@ -4,7 +4,6 @@ warning: missing documentation for the crate
 LL | / #![feature(rustdoc_missing_doc_code_examples)]
 LL | |
 LL | |
-LL | |
 ...  |
 LL | |
 LL | | pub fn foo() {}
@@ -39,7 +38,6 @@ warning: missing code example in this documentation
 LL | / #![feature(rustdoc_missing_doc_code_examples)]
 LL | |
 LL | |
-LL | |
 ...  |
 LL | |
 LL | | pub fn foo() {}

tests/ui/borrowck/issue-109271-pass-self-into-closure.stderr

@@ -42,8 +42,7 @@ LL |       v.call(|(), this: &mut S| {
    | |
 LL | |
 LL | |
-LL | |
-LL | |         _ = v;
+...  |
 LL | |         v.set();
    | |         - first borrow occurs due to use of `v` in closure
 ...  |

tests/ui/codemap_tests/huge_multispan_highlight.rs

@@ -5,6 +5,7 @@
 fn main() {
     let _ = match true {
         true => (
+            // last line shown in multispan header
 
 
 
@@ -95,27 +96,145 @@ fn main() {
 
         ),
         false => "
-        
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+
+        ",
+    };
+    let _ = match true {
+        true => (
+
+        1 // last line shown in multispan header
+
+
+
+
+
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+
+        ),
+        false => "
+
+
+        1 last line shown in multispan
+
+
+
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+
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+
         ",
     };
 }