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Add lint fn_null_check 
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‎CHANGELOG.md‎

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@@ -4203,6 +4203,7 @@ Released 2018-09-13
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[`float_cmp_const`]: https://rust-lang.github.io/rust-clippy/master/index.html#float_cmp_const
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[`float_equality_without_abs`]: https://rust-lang.github.io/rust-clippy/master/index.html#float_equality_without_abs
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[`fn_address_comparisons`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_address_comparisons
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[`fn_null_check`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_null_check
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[`fn_params_excessive_bools`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_params_excessive_bools
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[`fn_to_numeric_cast`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_to_numeric_cast
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[`fn_to_numeric_cast_any`]: https://rust-lang.github.io/rust-clippy/master/index.html#fn_to_numeric_cast_any

‎clippy_lints/src/declared_lints.rs‎

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@@ -161,6 +161,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
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crate::float_literal::LOSSY_FLOAT_LITERAL_INFO,
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crate::floating_point_arithmetic::IMPRECISE_FLOPS_INFO,
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crate::floating_point_arithmetic::SUBOPTIMAL_FLOPS_INFO,
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crate::fn_null_check::FN_NULL_CHECK_INFO,
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crate::format::USELESS_FORMAT_INFO,
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crate::format_args::FORMAT_IN_FORMAT_ARGS_INFO,
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crate::format_args::TO_STRING_IN_FORMAT_ARGS_INFO,

‎clippy_lints/src/fn_null_check.rs‎

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use clippy_utils::consts::{constant, Constant};
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use clippy_utils::diagnostics::span_lint_and_help;
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use clippy_utils::{is_integer_literal, is_path_diagnostic_item};
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use if_chain::if_chain;
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use rustc_hir::{BinOpKind, Expr, ExprKind, TyKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::sym;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for comparing a function pointer to null.
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///
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/// ### Why is this bad?
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/// Function pointers are assumed to not be null.
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///
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/// ### Example
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/// ```rust,ignore
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/// let fn_ptr: fn() = /* somehow obtained nullable function pointer */
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///
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/// if (fn_ptr as *const ()).is_null() { ... }
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/// ```
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/// Use instead:
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/// ```rust
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/// let fn_ptr: Option<fn()> = /* somehow obtained nullable function pointer */
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///
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/// if fn_ptr.is_none() { ... }
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/// ```
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#[clippy::version = "1.67.0"]
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pub FN_NULL_CHECK,
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correctness,
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"`fn()` type assumed to be nullable"
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}
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declare_lint_pass!(FnNullCheck => [FN_NULL_CHECK]);
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const LINT_MSG: &str = "function pointer assumed to be nullable, even though it isn't";
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const HELP_MSG: &str = "try wrapping your function pointer type in `Option<T>` instead, and using `is_none` to check for null pointer value";
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fn is_fn_ptr_cast(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
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if_chain! {
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if let ExprKind::Cast(cast_expr, cast_ty) = expr.kind;
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if let TyKind::Ptr(_) = cast_ty.kind;
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if cx.typeck_results().expr_ty_adjusted(cast_expr).is_fn();
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then {
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true
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} else {
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false
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}
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}
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}
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impl<'tcx> LateLintPass<'tcx> for FnNullCheck {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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// Catching:
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// (fn_ptr as *<const/mut> <ty>).is_null()
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if_chain! {
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if let ExprKind::MethodCall(method_name, receiver, _, _) = expr.kind;
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if method_name.ident.as_str() == "is_null";
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if is_fn_ptr_cast(cx, receiver);
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then {
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span_lint_and_help(
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cx,
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FN_NULL_CHECK,
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expr.span,
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LINT_MSG,
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None,
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HELP_MSG
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);
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}
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}
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if let ExprKind::Binary(op, left, right) = expr.kind
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&& let BinOpKind::Eq = op.node
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{
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let to_check: &Expr<'_>;
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if is_fn_ptr_cast(cx, left) {
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to_check = right;
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} else if is_fn_ptr_cast(cx, right) {
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to_check = left;
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} else {
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return;
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}
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// Catching:
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// (fn_ptr as *<const/mut> <ty>) == <const that evaluates to null_ptr>
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let c = constant(cx, cx.typeck_results(), to_check);
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if let Some((Constant::RawPtr(0), _)) = c {
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span_lint_and_help(
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cx,
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FN_NULL_CHECK,
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expr.span,
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LINT_MSG,
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None,
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HELP_MSG
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);
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return;
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}
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// Catching:
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// (fn_ptr as *<const/mut> <ty>) == (0 as <ty>)
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if let ExprKind::Cast(cast_expr, _) = to_check.kind && is_integer_literal(cast_expr, 0) {
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span_lint_and_help(
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cx,
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FN_NULL_CHECK,
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expr.span,
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LINT_MSG,
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None,
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HELP_MSG
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);
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return;
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}
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// Catching:
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// (fn_ptr as *<const/mut> <ty>) == std::ptr::null()
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if let ExprKind::Call(func, []) = to_check.kind &&
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is_path_diagnostic_item(cx, func, sym::ptr_null)
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{
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span_lint_and_help(
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cx,
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FN_NULL_CHECK,
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expr.span,
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LINT_MSG,
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None,
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HELP_MSG
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);
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}
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}
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}
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}

‎clippy_lints/src/transmute/transmute_null_to_fn.rs‎

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@@ -9,7 +9,7 @@ use rustc_span::symbol::sym;
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use super::TRANSMUTE_NULL_TO_FN;
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const LINT_MSG: &str = "transmuting a known null pointer into a function pointer";
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const NOTE_MSG: &str = "this transmute results in a null function pointer";
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const NOTE_MSG: &str = "this transmute results in undefined behavior";
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const HELP_MSG: &str =
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"try wrapping your function pointer type in `Option<T>` instead, and using `None` as a null pointer value";
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‎tests/ui/fn_null_check.rs‎

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#![allow(unused)]
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#![warn(clippy::fn_null_check)]
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#![allow(clippy::cmp_null)]
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#![allow(clippy::ptr_eq)]
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#![allow(clippy::zero_ptr)]
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pub const ZPTR: *const () = 0 as *const _;
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pub const NOT_ZPTR: *const () = 1 as *const _;
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fn main() {
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let fn_ptr = main;
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if (fn_ptr as *mut ()).is_null() {}
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if (fn_ptr as *const u8).is_null() {}
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if (fn_ptr as *const ()) == std::ptr::null() {}
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if (fn_ptr as *const ()) == (0 as *const ()) {}
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if (fn_ptr as *const ()) == ZPTR {}
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// no lint
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if (fn_ptr as *const ()) == NOT_ZPTR {}
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}

‎tests/ui/fn_null_check.stderr‎

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error: function pointer assumed to be nullable, even though it isn't
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--> $DIR/fn_null_check.rs:13:8
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|
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LL | if (fn_ptr as *mut ()).is_null() {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: try wrapping your function pointer type in `Option<T>` instead, and using `is_none` to check for null pointer value
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= note: `-D clippy::fn-null-check` implied by `-D warnings`
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error: function pointer assumed to be nullable, even though it isn't
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--> $DIR/fn_null_check.rs:14:8
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|
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LL | if (fn_ptr as *const u8).is_null() {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: try wrapping your function pointer type in `Option<T>` instead, and using `is_none` to check for null pointer value
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error: function pointer assumed to be nullable, even though it isn't
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--> $DIR/fn_null_check.rs:15:8
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|
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LL | if (fn_ptr as *const ()) == std::ptr::null() {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: try wrapping your function pointer type in `Option<T>` instead, and using `is_none` to check for null pointer value
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error: function pointer assumed to be nullable, even though it isn't
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--> $DIR/fn_null_check.rs:16:8
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|
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LL | if (fn_ptr as *const ()) == (0 as *const ()) {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: try wrapping your function pointer type in `Option<T>` instead, and using `is_none` to check for null pointer value
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error: function pointer assumed to be nullable, even though it isn't
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--> $DIR/fn_null_check.rs:17:8
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|
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LL | if (fn_ptr as *const ()) == ZPTR {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: try wrapping your function pointer type in `Option<T>` instead, and using `is_none` to check for null pointer value
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error: aborting due to 5 previous errors
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