emitter: current substitution can be multi-line

In `splice_lines`, there is some arithmetic to compute the required
alignment such that future substitutions in a suggestion are aligned
correctly. However, this assumed that the current substitution's span
was only on a single line. In circumstances where this was not true, it
could result in a arithmetic overflow when the substitution's end
column was less than the substitution's start column.

Signed-off-by: David Wood <david.wood@huawei.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 60a48b5a2d9..9b2094adb15 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -341,7 +341,7 @@ impl CodeSuggestion {
                     });
                     buf.push_str(&part.snippet);
                     let cur_hi = sm.lookup_char_pos(part.span.hi());
-                    if prev_hi.line == cur_lo.line {
+                    if prev_hi.line == cur_lo.line && cur_hi.line == cur_lo.line {
                         // Account for the difference between the width of the current code and the
                         // snippet being suggested, so that the *later* suggestions are correctly
                         // aligned on the screen.