Add invalid null pointer usage lint.

Author: boxdot

CHANGELOG.md

@@ -2266,6 +2266,7 @@ Released 2018-09-13
 [`into_iter_on_array`]: https://rust-lang.github.io/rust-clippy/master/index.html#into_iter_on_array
 [`into_iter_on_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#into_iter_on_ref
 [`invalid_atomic_ordering`]: https://rust-lang.github.io/rust-clippy/master/index.html#invalid_atomic_ordering
+[`invalid_null_usage`]: https://rust-lang.github.io/rust-clippy/master/index.html#invalid_null_usage
 [`invalid_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#invalid_ref
 [`invalid_regex`]: https://rust-lang.github.io/rust-clippy/master/index.html#invalid_regex
 [`invalid_upcast_comparisons`]: https://rust-lang.github.io/rust-clippy/master/index.html#invalid_upcast_comparisons

clippy_lints/src/lib.rs

@@ -901,6 +901,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &pattern_type_mismatch::PATTERN_TYPE_MISMATCH,
         &precedence::PRECEDENCE,
         &ptr::CMP_NULL,
+        &ptr::INVALID_NULL_USAGE,
         &ptr::MUT_FROM_REF,
         &ptr::PTR_ARG,
         &ptr_eq::PTR_EQ,
@@ -1669,6 +1670,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&partialeq_ne_impl::PARTIALEQ_NE_IMPL),
         LintId::of(&precedence::PRECEDENCE),
         LintId::of(&ptr::CMP_NULL),
+        LintId::of(&ptr::INVALID_NULL_USAGE),
         LintId::of(&ptr::MUT_FROM_REF),
         LintId::of(&ptr::PTR_ARG),
         LintId::of(&ptr_eq::PTR_EQ),
@@ -2007,6 +2009,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&non_octal_unix_permissions::NON_OCTAL_UNIX_PERMISSIONS),
         LintId::of(&open_options::NONSENSICAL_OPEN_OPTIONS),
         LintId::of(&option_env_unwrap::OPTION_ENV_UNWRAP),
+        LintId::of(&ptr::INVALID_NULL_USAGE),
         LintId::of(&ptr::MUT_FROM_REF),
         LintId::of(&ranges::REVERSED_EMPTY_RANGES),
         LintId::of(&regex::INVALID_REGEX),

clippy_lints/src/ptr.rs

@@ -119,7 +119,28 @@ declare_clippy_lint! {
     "fns that create mutable refs from immutable ref args"
 }
 
-declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF]);
+declare_clippy_lint! {
+    /// **What it does:** This lint checks for invalid usages of `ptr::null`.
+    ///
+    /// **Why is this bad?** This causes undefined behavior.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```ignore
+    /// // Bad. Undefined behavior
+    /// unsafe { std::slice::from_raw_parts(ptr::null(), 0); }
+    /// ```
+    ///
+    /// // Good
+    /// unsafe { std::slice::from_raw_parts(NonNull::dangling().as_ptr(), 0); }
+    /// ```
+    pub INVALID_NULL_USAGE,
+    correctness,
+    "invalid usage of a null pointer, suggesting `NonNull::dangling()` instead."
+}
+
+declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF, INVALID_NULL_USAGE]);
 
 impl<'tcx> LateLintPass<'tcx> for Ptr {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
@@ -161,6 +182,20 @@ impl<'tcx> LateLintPass<'tcx> for Ptr {
                     "comparing with null is better expressed by the `.is_null()` method",
                 );
             }
+        } else if let Some(args) = match_function_call(cx, expr, &paths::SLICE_FROM_RAW_PARTS) {
+            if let Some(arg) = args.first() {
+                if is_null_path(arg) {
+                    span_lint_and_sugg(
+                        cx,
+                        INVALID_NULL_USAGE,
+                        arg.span,
+                        "pointer must be non-null",
+                        "change this to",
+                        "core::ptr::NonNull::dangling().as_ptr()".to_string(),
+                        Applicability::MachineApplicable,
+                    );
+                }
+            }
         }
     }
 }

tests/ui/invalid_null_usage.fixed

@@ -0,0 +1,6 @@
+// run-rustfix
+
+fn main() {
+    let _slice: &[usize] = unsafe { std::slice::from_raw_parts(core::ptr::NonNull::dangling().as_ptr(), 0) };
+    let _slice: &[usize] = unsafe { std::slice::from_raw_parts(core::ptr::NonNull::dangling().as_ptr(), 0) };
+}

tests/ui/invalid_null_usage.rs

@@ -0,0 +1,6 @@
+// run-rustfix
+
+fn main() {
+    let _slice: &[usize] = unsafe { std::slice::from_raw_parts(std::ptr::null(), 0) };
+    let _slice: &[usize] = unsafe { std::slice::from_raw_parts(core::ptr::null(), 0) };
+}

tests/ui/invalid_null_usage.stderr

@@ -0,0 +1,16 @@
+error: pointer must be non-null
+  --> $DIR/invalid_null_usage.rs:4:64
+   |
+LL |     let _slice: &[usize] = unsafe { std::slice::from_raw_parts(std::ptr::null(), 0) };
+   |                                                                ^^^^^^^^^^^^^^^^ help: change this to: `core::ptr::NonNull::dangling().as_ptr()`
+   |
+   = note: `#[deny(clippy::invalid_null_usage)]` on by default
+
+error: pointer must be non-null
+  --> $DIR/invalid_null_usage.rs:5:64
+   |
+LL |     let _slice: &[usize] = unsafe { std::slice::from_raw_parts(core::ptr::null(), 0) };
+   |                                                                ^^^^^^^^^^^^^^^^^ help: change this to: `core::ptr::NonNull::dangling().as_ptr()`
+
+error: aborting due to 2 previous errors
+