extract each lint into its own module

Author: ada4a

clippy_lints/src/ptr/cmp_null.rs

@@ -0,0 +1,49 @@
+use super::CMP_NULL;
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::res::{MaybeDef, MaybeResPath};
+use clippy_utils::sugg::Sugg;
+use clippy_utils::{is_lint_allowed, sym};
+use rustc_errors::Applicability;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
+use rustc_lint::LateContext;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    op: BinOpKind,
+    l: &Expr<'_>,
+    r: &Expr<'_>,
+) -> bool {
+    let non_null_path_snippet = match (
+        is_lint_allowed(cx, CMP_NULL, expr.hir_id),
+        is_null_path(cx, l),
+        is_null_path(cx, r),
+    ) {
+        (false, true, false) if let Some(sugg) = Sugg::hir_opt(cx, r) => sugg.maybe_paren(),
+        (false, false, true) if let Some(sugg) = Sugg::hir_opt(cx, l) => sugg.maybe_paren(),
+        _ => return false,
+    };
+    let invert = if op == BinOpKind::Eq { "" } else { "!" };
+
+    span_lint_and_sugg(
+        cx,
+        CMP_NULL,
+        expr.span,
+        "comparing with null is better expressed by the `.is_null()` method",
+        "try",
+        format!("{invert}{non_null_path_snippet}.is_null()",),
+        Applicability::MachineApplicable,
+    );
+    true
+}
+
+fn is_null_path(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    if let ExprKind::Call(pathexp, []) = expr.kind {
+        matches!(
+            pathexp.basic_res().opt_diag_name(cx),
+            Some(sym::ptr_null | sym::ptr_null_mut)
+        )
+    } else {
+        false
+    }
+}