Avoid ICE if the Clone trait is not found while building error sugges…

…tions

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -739,13 +739,15 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let tcx = self.infcx.tcx;
         // Try to find predicates on *generic params* that would allow copying `ty`
         let infcx = tcx.infer_ctxt().build();
-        if infcx
-            .type_implements_trait(
-                tcx.lang_items().clone_trait().unwrap(),
-                [tcx.erase_regions(ty)],
-                self.param_env,
-            )
-            .must_apply_modulo_regions()
+
+        if let Some(clone_trait_def) = tcx.lang_items().clone_trait()
+            && infcx
+                .type_implements_trait(
+                    clone_trait_def,
+                    [tcx.erase_regions(ty)],
+                    self.param_env,
+                )
+                .must_apply_modulo_regions()
         {
             err.span_suggestion_verbose(
                 span.shrink_to_hi(),

src/test/ui/issues/issue-104870.rs

@@ -0,0 +1,19 @@
+// Avoid panicking if the Clone trait is not found while building error suggestions
+
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+
+#[lang = "copy"]
+trait Copy {}
+
+fn g<T>(x: T) {}
+
+fn f(x: *mut u8) {
+    g(x);
+    g(x); //~ ERROR use of moved value: `x`
+}
+
+fn main() {}

src/test/ui/issues/issue-104870.stderr

@@ -0,0 +1,21 @@
+error[E0382]: use of moved value: `x`
+  --> $DIR/issue-104870.rs:16:7
+   |
+LL | fn f(x: *mut u8) {
+   |      - move occurs because `x` has type `*mut u8`, which does not implement the `Copy` trait
+LL |     g(x);
+   |       - value moved here
+LL |     g(x);
+   |       ^ value used here after move
+   |
+note: consider changing this parameter type in function `g` to borrow instead if owning the value isn't necessary
+  --> $DIR/issue-104870.rs:12:12
+   |
+LL | fn g<T>(x: T) {}
+   |    -       ^ this parameter takes ownership of the value
+   |    |
+   |    in this function
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0382`.