From 3ddd82582543a3ab0c6abc01580a0ccb887f97c1 Mon Sep 17 00:00:00 2001
From: Lzu Tao <taolzu@gmail.com>
Date: Sun, 29 Sep 2019 13:22:44 +0000
Subject: [PATCH] Add suggestion for zero-ptr lint

---
 clippy_lints/src/misc.rs      | 20 ++++++++++++--------
 clippy_lints/src/utils/mod.rs |  2 +-
 tests/ui/zero_ptr.rs          | 11 +++++++----
 tests/ui/zero_ptr.stderr      | 16 ++++++++--------
 4 files changed, 28 insertions(+), 21 deletions(-)

diff --git a/clippy_lints/src/misc.rs b/clippy_lints/src/misc.rs
index 437114066cdf..501c13e6b952 100644
--- a/clippy_lints/src/misc.rs
+++ b/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! {
@@ -623,15 +623,19 @@ 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_fn) = match 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);
+            if let Some(ty_snip) = snippet_opt(cx, ty.span) {
+                let sugg = format!("{}::<{}>()", sugg_fn, ty_snip);
+                span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, Applicability::MachineApplicable)
+            } else {
+                span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", String::from(sugg_fn) + "()", Applicability::MaybeIncorrect)
+            }
         }
     }
 }
diff --git a/clippy_lints/src/utils/mod.rs b/clippy_lints/src/utils/mod.rs
index 8fd84c07a7d2..27dad6322d88 100644
--- a/clippy_lints/src/utils/mod.rs
+++ b/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
 /// }
 /// ```
diff --git a/tests/ui/zero_ptr.rs b/tests/ui/zero_ptr.rs
index 2291c77d56e6..4b3d751ae846 100644
--- a/tests/ui/zero_ptr.rs
+++ b/tests/ui/zero_ptr.rs
@@ -1,8 +1,11 @@
-#[allow(unused_variables)]
+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;
+
+    foo(0 as _, 0 as _);
 
     let z = 0;
-    let z = z as *const usize; // this is currently not caught
+    let _ = z as *const usize; // this is currently not caught
 }
diff --git a/tests/ui/zero_ptr.stderr b/tests/ui/zero_ptr.stderr
index b79c3457b9b3..8c006233b8f0 100644
--- a/tests/ui/zero_ptr.stderr
+++ b/tests/ui/zero_ptr.stderr
@@ -1,16 +1,16 @@
-error: `0 as *const _` detected. Consider using `ptr::null()`
-  --> $DIR/zero_ptr.rs:3:13
+error: `0 as *const _` detected
+  --> $DIR/zero_ptr.rs:4:13
    |
-LL |     let x = 0 as *const usize;
-   |             ^^^^^^^^^^^^^^^^^
+LL |     let _ = 0 as *const usize;
+   |             ^^^^^^^^^^^^^^^^^ help: try: `std::ptr::null::<*const 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:5:13
    |
-LL |     let y = 0 as *mut f64;
-   |             ^^^^^^^^^^^^^
+LL |     let _ = 0 as *mut f64;
+   |             ^^^^^^^^^^^^^ help: try: `std::ptr::null_mut::<*mut f64>()`
 
 error: aborting due to 2 previous errors