Add suggestion for zero-ptr lint

Author: tesuji

clippy_lints/src/misc.rs

@@ -13,8 +13,8 @@ use crate::consts::{constant, Constant};
 use crate::utils::sugg::Sugg;
 use crate::utils::{
     get_item_name, get_parent_expr, implements_trait, in_constant, is_integer_const, iter_input_pats,
-    last_path_segment, match_qpath, match_trait_method, paths, snippet, span_lint, span_lint_and_then,
-    span_lint_hir_and_then, walk_ptrs_ty, SpanlessEq,
+    last_path_segment, match_qpath, match_trait_method, paths, snippet, span_lint, span_lint_and_sugg,
+    span_lint_and_then, span_lint_hir_and_then, walk_ptrs_ty, SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -623,15 +623,14 @@ fn check_cast(cx: &LateContext<'_, '_>, span: Span, e: &Expr, ty: &Ty) {
     if_chain! {
         if let TyKind::Ptr(MutTy { mutbl, .. }) = ty.kind;
         if let ExprKind::Lit(ref lit) = e.kind;
-        if let LitKind::Int(value, ..) = lit.node;
-        if value == 0;
+        if let LitKind::Int(0, _) = lit.node;
         if !in_constant(cx, e.hir_id);
         then {
-            let msg = match mutbl {
-                Mutability::MutMutable => "`0 as *mut _` detected. Consider using `ptr::null_mut()`",
-                Mutability::MutImmutable => "`0 as *const _` detected. Consider using `ptr::null()`",
+            let (msg, sugg) = match mutbl {
+                Mutability::MutMutable => ("`0 as *mut _` detected. Consider using `ptr::null_mut()`", "std::ptr::null_mut()"),
+                Mutability::MutImmutable => ("`0 as *const _` detected. Consider using `ptr::null()`", "std::ptr::null()"),
             };
-            span_lint(cx, ZERO_PTR, span, msg);
+            span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg.to_string(), Applicability::MaybeIncorrect);
         }
     }
 }

tests/ui/zero_ptr.rs

@@ -1,8 +1,7 @@
-#[allow(unused_variables)]
 fn main() {
-    let x = 0 as *const usize;
-    let y = 0 as *mut f64;
+    let _ = 0 as *const usize;
+    let _ = 0 as *mut f64;
 
     let z = 0;
-    let z = z as *const usize; // this is currently not caught
+    let _ = z as *const usize; // this is currently not caught
 }

tests/ui/zero_ptr.stderr

@@ -1,16 +1,16 @@
 error: `0 as *const _` detected. Consider using `ptr::null()`
-  --> $DIR/zero_ptr.rs:3:13
+  --> $DIR/zero_ptr.rs:2:13
    |
-LL |     let x = 0 as *const usize;
-   |             ^^^^^^^^^^^^^^^^^
+LL |     let _ = 0 as *const usize;
+   |             ^^^^^^^^^^^^^^^^^ help: try: `std::ptr::null()`
    |
    = note: `-D clippy::zero-ptr` implied by `-D warnings`
 
 error: `0 as *mut _` detected. Consider using `ptr::null_mut()`
-  --> $DIR/zero_ptr.rs:4:13
+  --> $DIR/zero_ptr.rs:3:13
    |
-LL |     let y = 0 as *mut f64;
-   |             ^^^^^^^^^^^^^
+LL |     let _ = 0 as *mut f64;
+   |             ^^^^^^^^^^^^^ help: try: `std::ptr::null_mut()`
 
 error: aborting due to 2 previous errors