Rollup merge of #91273 - Badel2:ice-index-str, r=estebank

Fix ICE #91268 by checking that the snippet ends with a `)`

Fix #91268

Previously it was assumed that the last character of `snippet` will be a `)`, so using `snippet.len() - 1` as an index should be safe. However as we see in the test, it is possible to enter that branch without a closing `)`, and it will trigger the panic if the last character happens to be multibyte.

The fix is to ensure that the snippet ends with `)`, and skip the suggestion otherwise.

1 files changed, 13 insertions, 9 deletions

diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs
index cf0ee4fc28f..78afc339748 100644
--- a/compiler/rustc_ast_lowering/src/path.rs
+++ b/compiler/rustc_ast_lowering/src/path.rs
@@ -229,15 +229,19 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
                             // Do not suggest going from `Trait()` to `Trait<>`
                             if !data.inputs.is_empty() {
-                                if let Some(split) = snippet.find('(') {
-                                    let trait_name = &snippet[0..split];
-                                    let args = &snippet[split + 1..snippet.len() - 1];
-                                    err.span_suggestion(
-                                        data.span,
-                                        "use angle brackets instead",
-                                        format!("{}<{}>", trait_name, args),
-                                        Applicability::MaybeIncorrect,
-                                    );
+                                // Suggest replacing `(` and `)` with `<` and `>`
+                                // The snippet may be missing the closing `)`, skip that case
+                                if snippet.ends_with(')') {
+                                    if let Some(split) = snippet.find('(') {
+                                        let trait_name = &snippet[0..split];
+                                        let args = &snippet[split + 1..snippet.len() - 1];
+                                        err.span_suggestion(
+                                            data.span,
+                                            "use angle brackets instead",
+                                            format!("{}<{}>", trait_name, args),
+                                            Applicability::MaybeIncorrect,
+                                        );
+                                    }
                                 }
                             }
                         };