Auto merge of #4599 - lzutao:zero-ptr-suggestion, r=flip1995

Add suggestion for zero-ptr lint

changelog: Improve suggestion of `zero_ptr` lint

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, snippet_opt, span_lint, span_lint_and_sugg,
+    span_lint_and_then, span_lint_hir_and_then, walk_ptrs_ty, SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -621,17 +621,25 @@ fn non_macro_local(cx: &LateContext<'_, '_>, res: def::Res) -> bool {
 
 fn check_cast(cx: &LateContext<'_, '_>, span: Span, e: &Expr, ty: &Ty) {
     if_chain! {
-        if let TyKind::Ptr(MutTy { mutbl, .. }) = ty.kind;
+        if let TyKind::Ptr(ref mut_ty) = 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_fn) = match mut_ty.mutbl {
+                Mutability::MutMutable => ("`0 as *mut _` detected", "std::ptr::null_mut"),
+                Mutability::MutImmutable => ("`0 as *const _` detected", "std::ptr::null"),
             };
-            span_lint(cx, ZERO_PTR, span, msg);
+
+            let (sugg, appl) = if let TyKind::Infer = mut_ty.ty.kind {
+                (format!("{}()", sugg_fn), Applicability::MachineApplicable)
+            } else if let Some(mut_ty_snip) = snippet_opt(cx, mut_ty.ty.span) {
+                (format!("{}::<{}>()", sugg_fn, mut_ty_snip), Applicability::MachineApplicable)
+            } else {
+                // `MaybeIncorrect` as type inference may not work with the suggested code
+                (format!("{}()", sugg_fn), Applicability::MaybeIncorrect)
+            };
+            span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, appl);
         }
     }
 }

clippy_lints/src/utils/mod.rs

@@ -61,7 +61,7 @@ pub fn differing_macro_contexts(lhs: Span, rhs: Span) -> bool {
 /// # Example
 ///
 /// ```rust,ignore
-/// if in_constant(cx, expr.id) {
+/// if in_constant(cx, expr.hir_id) {
 ///     // Do something
 /// }
 /// ```

tests/ui/zero_ptr.fixed

@@ -0,0 +1,14 @@
+// run-rustfix
+pub fn foo(_const: *const f32, _mut: *mut i64) {}
+
+fn main() {
+    let _ = std::ptr::null::<usize>();
+    let _ = std::ptr::null_mut::<f64>();
+    let _: *const u8 = std::ptr::null();
+
+    foo(0 as _, 0 as _);
+    foo(std::ptr::null(), std::ptr::null_mut());
+
+    let z = 0;
+    let _ = z as *const usize; // this is currently not caught
+}

tests/ui/zero_ptr.rs

@@ -1,8 +1,14 @@
-#[allow(unused_variables)]
+// run-rustfix
+pub fn foo(_const: *const f32, _mut: *mut i64) {}
+
 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 _: *const u8 = 0 as *const _;
+
+    foo(0 as _, 0 as _);
+    foo(0 as *const _, 0 as *mut _);
 
     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 +1,34 @@
-error: `0 as *const _` detected. Consider using `ptr::null()`
-  --> $DIR/zero_ptr.rs:3:13
+error: `0 as *const _` detected
+  --> $DIR/zero_ptr.rs:5:13
    |
-LL |     let x = 0 as *const usize;
-   |             ^^^^^^^^^^^^^^^^^
+LL |     let _ = 0 as *const usize;
+   |             ^^^^^^^^^^^^^^^^^ help: try: `std::ptr::null::<usize>()`
    |
    = 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
+error: `0 as *mut _` detected
+  --> $DIR/zero_ptr.rs:6:13
    |
-LL |     let y = 0 as *mut f64;
-   |             ^^^^^^^^^^^^^
+LL |     let _ = 0 as *mut f64;
+   |             ^^^^^^^^^^^^^ help: try: `std::ptr::null_mut::<f64>()`
 
-error: aborting due to 2 previous errors
+error: `0 as *const _` detected
+  --> $DIR/zero_ptr.rs:7:24
+   |
+LL |     let _: *const u8 = 0 as *const _;
+   |                        ^^^^^^^^^^^^^ help: try: `std::ptr::null()`
+
+error: `0 as *const _` detected
+  --> $DIR/zero_ptr.rs:10:9
+   |
+LL |     foo(0 as *const _, 0 as *mut _);
+   |         ^^^^^^^^^^^^^ help: try: `std::ptr::null()`
+
+error: `0 as *mut _` detected
+  --> $DIR/zero_ptr.rs:10:24
+   |
+LL |     foo(0 as *const _, 0 as *mut _);
+   |                        ^^^^^^^^^^^ help: try: `std::ptr::null_mut()`
+
+error: aborting due to 5 previous errors