Auto merge of #10023 - Jarcho:issue_10017, r=xFrednet

Fix `zero_ptr` suggestion for `no_std` crates

fixes #10017

---

changelog: Sugg: [`zero_ptr`]: Now suggests `core::` paths for `no_std` crates
[#10023](https://github.com/rust-lang/rust-clippy/pull/10023)

5 files changed, 111 insertions, 25 deletions

diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 3bcc2216f52..aa22d923f14 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -538,7 +538,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::new(needless_bool::NeedlessBool));
     store.register_late_pass(|_| Box::new(needless_bool::BoolComparison));
     store.register_late_pass(|_| Box::new(needless_for_each::NeedlessForEach));
-    store.register_late_pass(|_| Box::new(misc::MiscLints));
+    store.register_late_pass(|_| Box::<misc::LintPass>::default());
     store.register_late_pass(|_| Box::new(eta_reduction::EtaReduction));
     store.register_late_pass(|_| Box::new(mut_mut::MutMut));
     store.register_late_pass(|_| Box::new(mut_reference::UnnecessaryMutPassed));
diff --git a/clippy_lints/src/misc.rs b/clippy_lints/src/misc.rs
index 516dee20f8b..9f4beb92b9d 100644
--- a/clippy_lints/src/misc.rs
+++ b/clippy_lints/src/misc.rs
@@ -9,12 +9,14 @@ use rustc_hir::{
 };
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::lint::in_external_macro;
-use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::hygiene::DesugaringKind;
 use rustc_span::source_map::{ExpnKind, Span};
 
 use clippy_utils::sugg::Sugg;
-use clippy_utils::{get_parent_expr, in_constant, is_integer_literal, iter_input_pats, last_path_segment, SpanlessEq};
+use clippy_utils::{
+    get_parent_expr, in_constant, is_integer_literal, is_no_std_crate, iter_input_pats, last_path_segment, SpanlessEq,
+};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -120,14 +122,28 @@ declare_clippy_lint! {
     "using `0 as *{const, mut} T`"
 }
 
-declare_lint_pass!(MiscLints => [
+pub struct LintPass {
+    std_or_core: &'static str,
+}
+impl Default for LintPass {
+    fn default() -> Self {
+        Self { std_or_core: "std" }
+    }
+}
+impl_lint_pass!(LintPass => [
     TOPLEVEL_REF_ARG,
     USED_UNDERSCORE_BINDING,
     SHORT_CIRCUIT_STATEMENT,
     ZERO_PTR,
 ]);
 
-impl<'tcx> LateLintPass<'tcx> for MiscLints {
+impl<'tcx> LateLintPass<'tcx> for LintPass {
+    fn check_crate(&mut self, cx: &LateContext<'_>) {
+        if is_no_std_crate(cx) {
+            self.std_or_core = "core";
+        }
+    }
+
     fn check_fn(
         &mut self,
         cx: &LateContext<'tcx>,
@@ -231,7 +247,7 @@ impl<'tcx> LateLintPass<'tcx> for MiscLints {
 
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if let ExprKind::Cast(e, ty) = expr.kind {
-            check_cast(cx, expr.span, e, ty);
+            self.check_cast(cx, expr.span, e, ty);
             return;
         }
         if in_attributes_expansion(expr) || expr.span.is_desugaring(DesugaringKind::Await) {
@@ -310,26 +326,28 @@ fn non_macro_local(cx: &LateContext<'_>, res: def::Res) -> bool {
     }
 }
 
-fn check_cast(cx: &LateContext<'_>, span: Span, e: &Expr<'_>, ty: &hir::Ty<'_>) {
-    if_chain! {
-        if let TyKind::Ptr(ref mut_ty) = ty.kind;
-        if is_integer_literal(e, 0);
-        if !in_constant(cx, e.hir_id);
-        then {
-            let (msg, sugg_fn) = match mut_ty.mutbl {
-                Mutability::Mut => ("`0 as *mut _` detected", "std::ptr::null_mut"),
-                Mutability::Not => ("`0 as *const _` detected", "std::ptr::null"),
-            };
+impl LintPass {
+    fn check_cast(&self, cx: &LateContext<'_>, span: Span, e: &Expr<'_>, ty: &hir::Ty<'_>) {
+        if_chain! {
+            if let TyKind::Ptr(ref mut_ty) = ty.kind;
+            if is_integer_literal(e, 0);
+            if !in_constant(cx, e.hir_id);
+            then {
+                let (msg, sugg_fn) = match mut_ty.mutbl {
+                    Mutability::Mut => ("`0 as *mut _` detected", "ptr::null_mut"),
+                    Mutability::Not => ("`0 as *const _` detected", "ptr::null"),
+                };
 
-            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);
+                let (sugg, appl) = if let TyKind::Infer = mut_ty.ty.kind {
+                    (format!("{}::{sugg_fn}()", self.std_or_core), Applicability::MachineApplicable)
+                } else if let Some(mut_ty_snip) = snippet_opt(cx, mut_ty.ty.span) {
+                    (format!("{}::{sugg_fn}::<{mut_ty_snip}>()", self.std_or_core), Applicability::MachineApplicable)
+                } else {
+                    // `MaybeIncorrect` as type inference may not work with the suggested code
+                    (format!("{}::{sugg_fn}()", self.std_or_core), Applicability::MaybeIncorrect)
+                };
+                span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, appl);
+            }
         }
     }
 }
diff --git a/tests/ui/zero_ptr_no_std.fixed b/tests/ui/zero_ptr_no_std.fixed
new file mode 100644
index 00000000000..8906c776977
--- /dev/null
+++ b/tests/ui/zero_ptr_no_std.fixed
@@ -0,0 +1,21 @@
+// run-rustfix
+
+#![feature(lang_items, start, libc)]
+#![no_std]
+#![deny(clippy::zero_ptr)]
+
+#[start]
+fn main(_argc: isize, _argv: *const *const u8) -> isize {
+    let _ = core::ptr::null::<usize>();
+    let _ = core::ptr::null_mut::<f64>();
+    let _: *const u8 = core::ptr::null();
+    0
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"]
+extern "C" fn eh_personality() {}
diff --git a/tests/ui/zero_ptr_no_std.rs b/tests/ui/zero_ptr_no_std.rs
new file mode 100644
index 00000000000..379c1b18d29
--- /dev/null
+++ b/tests/ui/zero_ptr_no_std.rs
@@ -0,0 +1,21 @@
+// run-rustfix
+
+#![feature(lang_items, start, libc)]
+#![no_std]
+#![deny(clippy::zero_ptr)]
+
+#[start]
+fn main(_argc: isize, _argv: *const *const u8) -> isize {
+    let _ = 0 as *const usize;
+    let _ = 0 as *mut f64;
+    let _: *const u8 = 0 as *const _;
+    0
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"]
+extern "C" fn eh_personality() {}
diff --git a/tests/ui/zero_ptr_no_std.stderr b/tests/ui/zero_ptr_no_std.stderr
new file mode 100644
index 00000000000..d92bb4a6528
--- /dev/null
+++ b/tests/ui/zero_ptr_no_std.stderr
@@ -0,0 +1,26 @@
+error: `0 as *const _` detected
+  --> $DIR/zero_ptr_no_std.rs:9:13
+   |
+LL |     let _ = 0 as *const usize;
+   |             ^^^^^^^^^^^^^^^^^ help: try: `core::ptr::null::<usize>()`
+   |
+note: the lint level is defined here
+  --> $DIR/zero_ptr_no_std.rs:5:9
+   |
+LL | #![deny(clippy::zero_ptr)]
+   |         ^^^^^^^^^^^^^^^^
+
+error: `0 as *mut _` detected
+  --> $DIR/zero_ptr_no_std.rs:10:13
+   |
+LL |     let _ = 0 as *mut f64;
+   |             ^^^^^^^^^^^^^ help: try: `core::ptr::null_mut::<f64>()`
+
+error: `0 as *const _` detected
+  --> $DIR/zero_ptr_no_std.rs:11:24
+   |
+LL |     let _: *const u8 = 0 as *const _;
+   |                        ^^^^^^^^^^^^^ help: try: `core::ptr::null()`
+
+error: aborting due to 3 previous errors
+