instantly_dangling_pointer: fix ICE

Turns out you cannot format Ty's you won't emit in unsuppressed diagnostics

Author: GrigorenkoPV

compiler/rustc_lint/src/dangling.rs

@@ -49,14 +49,19 @@ impl<'tcx> LateLintPass<'tcx> for DanglingPointers {
             && as_ptr_path.ident.name == sym::as_ptr
             && let ExprKind::MethodCall(unwrap_path, unwrap_receiver, ..) = as_ptr_receiver.kind
             && (unwrap_path.ident.name == sym::unwrap || unwrap_path.ident.name == sym::expect)
-            && lint_cstring_as_ptr(cx, unwrap_receiver)
+            && let source_type = cx.typeck_results().expr_ty(unwrap_receiver)
+            && let ty::Adt(def, args) = source_type.kind()
+            && cx.tcx.is_diagnostic_item(sym::Result, def.did())
+            && let ty = args.type_at(0)
+            && let ty::Adt(adt, _) = ty.kind()
+            && cx.tcx.is_diagnostic_item(sym::cstring_type, adt.did())
         {
             cx.emit_span_lint(
                 TEMPORARY_CSTRING_AS_PTR,
                 as_ptr_path.ident.span,
                 InstantlyDangling {
                     callee: as_ptr_path.ident.name,
-                    ty: "CString".into(),
+                    ty,
                     ptr_span: as_ptr_path.ident.span,
                     temporary_span: as_ptr_receiver.span,
                 },
@@ -75,7 +80,7 @@ impl<'tcx> LateLintPass<'tcx> for DanglingPointers {
                 method.ident.span,
                 InstantlyDangling {
                     callee: method.ident.name,
-                    ty: ty.to_string(),
+                    ty,
                     ptr_span: method.ident.span,
                     temporary_span: receiver.span,
                 },
@@ -84,20 +89,6 @@ impl<'tcx> LateLintPass<'tcx> for DanglingPointers {
     }
 }
 
-fn lint_cstring_as_ptr(cx: &LateContext<'_>, source: &rustc_hir::Expr<'_>) -> bool {
-    let source_type = cx.typeck_results().expr_ty(source);
-    if let ty::Adt(def, args) = source_type.kind() {
-        if cx.tcx.is_diagnostic_item(sym::Result, def.did()) {
-            if let ty::Adt(adt, _) = args.type_at(0).kind() {
-                if cx.tcx.is_diagnostic_item(sym::cstring_type, adt.did()) {
-                    return true;
-                }
-            }
-        }
-    }
-    false
-}
-
 fn is_temporary_rvalue(expr: &Expr<'_>) -> bool {
     match expr.kind {
         // Const is not temporary.

compiler/rustc_lint/src/lints.rs

@@ -1130,9 +1130,9 @@ pub struct IgnoredUnlessCrateSpecified<'a> {
 #[note]
 #[help]
 // FIXME: use #[primary_span]
-pub struct InstantlyDangling {
+pub struct InstantlyDangling<'tcx> {
     pub callee: Symbol,
-    pub ty: String,
+    pub ty: Ty<'tcx>,
     #[label(lint_label_ptr)]
     pub ptr_span: Span,
     #[label(lint_label_temporary)]

tests/ui/lint/dangling-ptr/instantly-dangling-pointer-allow.rs

@@ -0,0 +1,9 @@
+//@ check-pass
+
+// This should not ICE.
+
+#![allow(instantly_dangling_pointer)]
+
+fn main() {
+    dbg!(String::new().as_ptr());
+}