Do not ICE with incorrect empty suggestion

compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs

@@ -1048,7 +1048,18 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
                 },
             );
 
-            err.span_suggestion(span, msg, "", Applicability::MaybeIncorrect);
+            if span.is_empty() {
+                // HACK: Avoid ICE when types with the same name with `derive`s are in the same scope:
+                //     struct NotSM;
+                //     #[derive(PartialEq, Eq)]
+                //     struct NotSM<T>(T);
+                // With the above code, the suggestion would be to remove the generics of the first
+                // `NotSM`, which doesn't *have* generics, so we would suggest to remove no code with
+                // no code, which would trigger an `assert!` later. Ideally, we would do something a
+                // bit more principled. See closed PR #109082.
+            } else {
+                err.span_suggestion(span, msg, "", Applicability::MaybeIncorrect);
+            }
         } else if redundant_lifetime_args && redundant_type_or_const_args {
             remove_lifetime_args(err);
             remove_type_or_const_args(err);

tests/ui/duplicate/multiple-types-with-same-name-and-derive.rs

@@ -0,0 +1,19 @@
+// Here, there are two types with the same name. One of these has a `derive` annotation, but in the
+// expansion these `impl`s are associated to the the *other* type. There is a suggestion to remove
+// unneded type parameters, but because we're now point at a type with no type parameters, the
+// suggestion would suggest removing code from an empty span, which would ICE in nightly.
+//
+// issue: rust-lang/rust#108748
+
+struct NotSM;
+
+#[derive(PartialEq, Eq)]
+//~^ ERROR struct takes 0 generic arguments
+//~| ERROR struct takes 0 generic arguments
+//~| ERROR struct takes 0 generic arguments
+//~| ERROR struct takes 0 generic arguments
+struct NotSM<T>(T);
+//~^ ERROR the name `NotSM` is defined multiple times
+//~| ERROR no field `0`
+
+fn main() {}

tests/ui/duplicate/multiple-types-with-same-name-and-derive.stderr

@@ -0,0 +1,71 @@
+error[E0428]: the name `NotSM` is defined multiple times
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:15:1
+   |
+LL | struct NotSM;
+   | ------------- previous definition of the type `NotSM` here
+...
+LL | struct NotSM<T>(T);
+   | ^^^^^^^^^^^^^^^^^^^ `NotSM` redefined here
+   |
+   = note: `NotSM` must be defined only once in the type namespace of this module
+
+error[E0107]: struct takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:10:10
+   |
+LL | #[derive(PartialEq, Eq)]
+   |          ^^^^^^^^^ expected 0 generic arguments
+   |
+note: struct defined here, with 0 generic parameters
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:8:8
+   |
+LL | struct NotSM;
+   |        ^^^^^
+
+error[E0107]: struct takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:10:10
+   |
+LL | #[derive(PartialEq, Eq)]
+   |          ^^^^^^^^^ expected 0 generic arguments
+   |
+note: struct defined here, with 0 generic parameters
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:8:8
+   |
+LL | struct NotSM;
+   |        ^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error[E0107]: struct takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:10:21
+   |
+LL | #[derive(PartialEq, Eq)]
+   |                     ^^ expected 0 generic arguments
+   |
+note: struct defined here, with 0 generic parameters
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:8:8
+   |
+LL | struct NotSM;
+   |        ^^^^^
+
+error[E0107]: struct takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:10:10
+   |
+LL | #[derive(PartialEq, Eq)]
+   |          ^^^^^^^^^ expected 0 generic arguments
+   |
+note: struct defined here, with 0 generic parameters
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:8:8
+   |
+LL | struct NotSM;
+   |        ^^^^^
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error[E0609]: no field `0` on type `&NotSM`
+  --> $DIR/multiple-types-with-same-name-and-derive.rs:15:17
+   |
+LL | struct NotSM<T>(T);
+   |                 ^ unknown field
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0107, E0428, E0609.
+For more information about an error, try `rustc --explain E0107`.