Rollup merge of rust-lang#89912 - davidtwco:issue-89280-split-lines-m…

…ultiple-lines, r=oli-obk

emitter: current substitution can be multi-line

Fixes rust-lang#89280.

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.

r? ```@oli-obk```

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.

src/test/ui/errors/issue-89280-emitter-overflow-splice-lines.rs

@@ -0,0 +1,10 @@
+// check-pass
+
+trait X {
+ fn test(x: u32, (
+//~^ WARN anonymous parameters are deprecated and will be removed in the next edition
+//~^^ WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
+ )) {}
+}
+
+fn main() {}

src/test/ui/errors/issue-89280-emitter-overflow-splice-lines.stderr

@@ -0,0 +1,23 @@
+warning: anonymous parameters are deprecated and will be removed in the next edition
+ --> $DIR/issue-89280-emitter-overflow-splice-lines.rs:4:21
+ |
+LL | fn test(x: u32, (
+ | _____________________^
+LL | |
+LL | |
+LL | | )) {}
+ | |_____^
+ |
+ = note: `#[warn(anonymous_parameters)]` on by default
+ = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
+ = note: for more information, see issue #41686 <https://github.com/rust-lang/rust/issues/41686>
+help: try naming the parameter or explicitly ignoring it
+ |
+LL ~ fn test(x: u32, _: (
+LL +
+LL +
+LL ~ )) {}
+ |
+
+warning: 1 warning emitted
+