remove expect() in unnecessary_transmutes

compiler/rustc_mir_transform/src/check_unnecessary_transmutes.rs

@@ -87,11 +87,8 @@ impl<'tcx> Visitor<'tcx> for UnnecessaryTransmuteChecker<'_, 'tcx> {
             && let Some((func_def_id, _)) = func.const_fn_def()
             && self.tcx.is_intrinsic(func_def_id, sym::transmute)
             && let span = self.body.source_info(location).span
-            && let Some(lint) = self.is_unnecessary_transmute(
-                func,
-                self.tcx.sess.source_map().span_to_snippet(arg).expect("ok"),
-                span,
-            )
+            && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(arg)
+            && let Some(lint) = self.is_unnecessary_transmute(func, snippet, span)
             && let Some(hir_id) = terminator.source_info.scope.lint_root(&self.body.source_scopes)
         {
             self.tcx.emit_node_span_lint(UNNECESSARY_TRANSMUTES, hir_id, span, lint);

tests/ui/transmute/auxiliary/unnecessary-transmute-path-remap-ice-140277-trans.rs

@@ -0,0 +1,10 @@
+//@ compile-flags: --remap-path-prefix=/=/non-existent
+// helper for ../unnecessary-transmute-path-remap-ice-140277.rs
+
+#[macro_export]
+macro_rules! transmute {
+    ($e:expr) => {{
+        let e = $e;
+        std::mem::transmute(e)
+    }};
+}

tests/ui/transmute/unnecessary-transmute-path-remap-ice-140277.rs

@@ -0,0 +1,10 @@
+//@ aux-crate: zerocopy=unnecessary-transmute-path-remap-ice-140277-trans.rs
+//@ check-pass
+// tests for a regression in linting for unnecessary transmutes
+// where a span was inacessible for snippet procuring,
+// when remap-path-prefix was set, causing a panic.
+
+fn bytes_at_home(x: [u8; 4]) -> u32 {
+    unsafe { zerocopy::transmute!(x) }
+}
+fn main() {}