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Uplift clippy::fn_null_check to rustc
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6 files changed

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‎compiler/rustc_lint/messages.ftl

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@@ -215,6 +215,9 @@ lint_expectation = this lint expectation is unfulfilled
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.note = the `unfulfilled_lint_expectations` lint can't be expected and will always produce this message
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.rationale = {$rationale}
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lint_fn_null_check = function pointers are not nullable, so checking them for null will always return false
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.help = wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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lint_for_loops_over_fallibles =
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for loop over {$article} `{$ty}`. This is more readably written as an `if let` statement
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.suggestion = consider using `if let` to clear intent

‎compiler/rustc_lint/src/fn_null_check.rs

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@@ -0,0 +1,112 @@
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use crate::{lints::FnNullCheckDiag, LateContext, LateLintPass, LintContext};
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use rustc_ast::LitKind;
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use rustc_hir::{BinOpKind, Expr, ExprKind, TyKind};
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use rustc_session::{declare_lint, declare_lint_pass};
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use rustc_span::sym;
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declare_lint! {
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/// The `incorrect_fn_null_checks` lint checks for expression that checks if a
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/// function pointer is null.
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///
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/// ### Example
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///
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/// ```rust
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/// # fn test() {}
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/// let fn_ptr: fn() = /* somehow obtained nullable function pointer */
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/// # test;
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///
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/// if (fn_ptr as *const ()).is_null() { /* ... */ }
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/// ```
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///
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/// {{produces}}
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///
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/// ### Explanation
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///
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/// Function pointers are assumed to be non-null, checking them for null will always
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/// return false.
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INCORRECT_FN_NULL_CHECKS,
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Warn,
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"incorrect checking of null function pointer"
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}
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declare_lint_pass!(IncorrectFnNullChecks => [INCORRECT_FN_NULL_CHECKS]);
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fn is_fn_ptr_cast(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
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let mut expr = expr.peel_blocks();
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let mut had_at_least_one_cast = false;
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while let ExprKind::Cast(cast_expr, cast_ty) = expr.kind
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&& let TyKind::Ptr(_) = cast_ty.kind {
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expr = cast_expr.peel_blocks();
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had_at_least_one_cast = true;
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}
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had_at_least_one_cast && cx.typeck_results().expr_ty_adjusted(expr).is_fn()
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}
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impl<'tcx> LateLintPass<'tcx> for IncorrectFnNullChecks {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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match expr.kind {
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// Catching:
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// <*<const/mut> <ty>>::is_null(fn_ptr as *<const/mut> <ty>)
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ExprKind::Call(path, [arg])
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if let ExprKind::Path(ref qpath) = path.kind
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&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
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&& matches!(
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cx.tcx.get_diagnostic_name(def_id),
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Some(sym::ptr_const_is_null | sym::ptr_is_null)
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)
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&& is_fn_ptr_cast(cx, arg) =>
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{
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cx.emit_spanned_lint(INCORRECT_FN_NULL_CHECKS, expr.span, FnNullCheckDiag)
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}
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// Catching:
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// (fn_ptr as *<const/mut> <ty>).is_null()
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ExprKind::MethodCall(_, receiver, _, _)
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if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
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&& matches!(
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cx.tcx.get_diagnostic_name(def_id),
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Some(sym::ptr_const_is_null | sym::ptr_is_null)
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)
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&& is_fn_ptr_cast(cx, receiver) =>
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{
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cx.emit_spanned_lint(INCORRECT_FN_NULL_CHECKS, expr.span, FnNullCheckDiag)
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}
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ExprKind::Binary(op, left, right) if matches!(op.node, BinOpKind::Eq) => {
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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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match to_check.kind {
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// Catching:
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// (fn_ptr as *<const/mut> <ty>) == (0 as <ty>)
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ExprKind::Cast(cast_expr, _)
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if let ExprKind::Lit(spanned) = cast_expr.kind
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&& let LitKind::Int(v, _) = spanned.node && v == 0 =>
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{
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cx.emit_spanned_lint(INCORRECT_FN_NULL_CHECKS, expr.span, FnNullCheckDiag)
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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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ExprKind::Call(path, [])
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if let ExprKind::Path(ref qpath) = path.kind
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&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
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&& let Some(diag_item) = cx.tcx.get_diagnostic_name(def_id)
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&& (diag_item == sym::ptr_null || diag_item == sym::ptr_null_mut) =>
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{
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cx.emit_spanned_lint(INCORRECT_FN_NULL_CHECKS, expr.span, FnNullCheckDiag)
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},
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_ => {},
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}
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}
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_ => {}
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}
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}
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}

‎compiler/rustc_lint/src/lib.rs

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@@ -58,6 +58,7 @@ mod early;
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mod enum_intrinsics_non_enums;
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mod errors;
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mod expect;
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mod fn_null_check;
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mod for_loops_over_fallibles;
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pub mod hidden_unicode_codepoints;
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mod internal;
@@ -102,6 +103,7 @@ use cast_ref_to_mut::*;
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use deref_into_dyn_supertrait::*;
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use drop_forget_useless::*;
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use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
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use fn_null_check::*;
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use for_loops_over_fallibles::*;
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use hidden_unicode_codepoints::*;
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use internal::*;
@@ -225,6 +227,7 @@ late_lint_methods!(
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// Depends on types used in type definitions
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MissingCopyImplementations: MissingCopyImplementations,
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// Depends on referenced function signatures in expressions
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IncorrectFnNullChecks: IncorrectFnNullChecks,
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MutableTransmutes: MutableTransmutes,
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TypeAliasBounds: TypeAliasBounds,
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TrivialConstraints: TrivialConstraints,

‎compiler/rustc_lint/src/lints.rs

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@@ -613,6 +613,12 @@ pub struct ExpectationNote {
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pub rationale: Symbol,
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}
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// fn_null_check.rs
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#[derive(LintDiagnostic)]
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#[diag(lint_fn_null_check)]
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#[help]
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pub struct FnNullCheckDiag;
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// for_loops_over_fallibles.rs
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#[derive(LintDiagnostic)]
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#[diag(lint_for_loops_over_fallibles)]

‎tests/ui/lint/fn_null_check.rs

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@@ -0,0 +1,30 @@
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// check-pass
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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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//~^ WARN function pointers are not nullable
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if (fn_ptr as *const u8).is_null() {}
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//~^ WARN function pointers are not nullable
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if (fn_ptr as *const ()) == std::ptr::null() {}
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//~^ WARN function pointers are not nullable
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if (fn_ptr as *mut ()) == std::ptr::null_mut() {}
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//~^ WARN function pointers are not nullable
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if (fn_ptr as *const ()) == (0 as *const ()) {}
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//~^ WARN function pointers are not nullable
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if <*const _>::is_null(fn_ptr as *const ()) {}
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//~^ WARN function pointers are not nullable
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if (fn_ptr as *mut fn() as *const fn() as *const ()).is_null() {}
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//~^ WARN function pointers are not nullable
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if (fn_ptr as fn() as *const ()).is_null() {}
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//~^ WARN function pointers are not nullable
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const ZPTR: *const () = 0 as *const _;
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const NOT_ZPTR: *const () = 1 as *const _;
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// unlike the uplifted clippy::fn_null_check lint we do
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// not lint on them
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if (fn_ptr as *const ()) == ZPTR {}
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if (fn_ptr as *const ()) == NOT_ZPTR {}
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}

‎tests/ui/lint/fn_null_check.stderr

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warning: function pointers are not nullable, so checking them for null will always return false
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--> $DIR/fn_null_check.rs:6:8
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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: wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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= note: `#[warn(incorrect_fn_null_checks)]` on by default
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warning: function pointers are not nullable, so checking them for null will always return false
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--> $DIR/fn_null_check.rs:8:8
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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: wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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warning: function pointers are not nullable, so checking them for null will always return false
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--> $DIR/fn_null_check.rs:10:8
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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: wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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warning: function pointers are not nullable, so checking them for null will always return false
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--> $DIR/fn_null_check.rs:12:8
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|
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LL | if (fn_ptr as *mut ()) == std::ptr::null_mut() {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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warning: function pointers are not nullable, so checking them for null will always return false
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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 ()) == (0 as *const ()) {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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warning: function pointers are not nullable, so checking them for null will always return false
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--> $DIR/fn_null_check.rs:16:8
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|
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LL | if <*const _>::is_null(fn_ptr as *const ()) {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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warning: function pointers are not nullable, so checking them for null will always return false
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--> $DIR/fn_null_check.rs:18:8
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|
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LL | if (fn_ptr as *mut fn() as *const fn() as *const ()).is_null() {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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warning: function pointers are not nullable, so checking them for null will always return false
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--> $DIR/fn_null_check.rs:20:8
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|
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LL | if (fn_ptr as fn() as *const ()).is_null() {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= help: wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
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warning: 8 warnings emitted
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