Auto merge of #8905 - c410-f3r:arith, r=llogiq

[1/N] Implement Arithmetic lint

Assuming that https://github.com/rust-lang/rust-clippy/issues/8903 is OK, this PR starts the creation of the `Arithmetic` lint with configurable types.

My current struggle to get a rustc review inspired me to create smaller PRs in order to easy review and make merges as fast as possible. So the first step here only moves the `arithmetic.rs` file to `numeric_arithmetic.rs` to make room for the new lint.

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changelog: none

1 files changed, 170 insertions, 0 deletions

diff --git a/clippy_lints/src/numeric_arithmetic.rs b/clippy_lints/src/numeric_arithmetic.rs
new file mode 100644
index 00000000000..5c4de338149
--- /dev/null
+++ b/clippy_lints/src/numeric_arithmetic.rs
@@ -0,0 +1,170 @@
+use clippy_utils::consts::constant_simple;
+use clippy_utils::diagnostics::span_lint;
+use rustc_hir as hir;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::source_map::Span;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for integer arithmetic operations which could overflow or panic.
+    ///
+    /// Specifically, checks for any operators (`+`, `-`, `*`, `<<`, etc) which are capable
+    /// of overflowing according to the [Rust
+    /// Reference](https://doc.rust-lang.org/reference/expressions/operator-expr.html#overflow),
+    /// or which can panic (`/`, `%`). No bounds analysis or sophisticated reasoning is
+    /// attempted.
+    ///
+    /// ### Why is this bad?
+    /// Integer overflow will trigger a panic in debug builds or will wrap in
+    /// release mode. Division by zero will cause a panic in either mode. In some applications one
+    /// wants explicitly checked, wrapping or saturating arithmetic.
+    ///
+    /// ### Example
+    /// ```rust
+    /// # let a = 0;
+    /// a + 1;
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub INTEGER_ARITHMETIC,
+    restriction,
+    "any integer arithmetic expression which could overflow or panic"
+}
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for float arithmetic.
+    ///
+    /// ### Why is this bad?
+    /// For some embedded systems or kernel development, it
+    /// can be useful to rule out floating-point numbers.
+    ///
+    /// ### Example
+    /// ```rust
+    /// # let a = 0.0;
+    /// a + 1.0;
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub FLOAT_ARITHMETIC,
+    restriction,
+    "any floating-point arithmetic statement"
+}
+
+#[derive(Copy, Clone, Default)]
+pub struct NumericArithmetic {
+    expr_span: Option<Span>,
+    /// This field is used to check whether expressions are constants, such as in enum discriminants
+    /// and consts
+    const_span: Option<Span>,
+}
+
+impl_lint_pass!(NumericArithmetic => [INTEGER_ARITHMETIC, FLOAT_ARITHMETIC]);
+
+impl<'tcx> LateLintPass<'tcx> for NumericArithmetic {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
+        if self.expr_span.is_some() {
+            return;
+        }
+
+        if let Some(span) = self.const_span {
+            if span.contains(expr.span) {
+                return;
+            }
+        }
+        match &expr.kind {
+            hir::ExprKind::Binary(op, l, r) | hir::ExprKind::AssignOp(op, l, r) => {
+                match op.node {
+                    hir::BinOpKind::And
+                    | hir::BinOpKind::Or
+                    | hir::BinOpKind::BitAnd
+                    | hir::BinOpKind::BitOr
+                    | hir::BinOpKind::BitXor
+                    | hir::BinOpKind::Eq
+                    | hir::BinOpKind::Lt
+                    | hir::BinOpKind::Le
+                    | hir::BinOpKind::Ne
+                    | hir::BinOpKind::Ge
+                    | hir::BinOpKind::Gt => return,
+                    _ => (),
+                }
+
+                let (l_ty, r_ty) = (cx.typeck_results().expr_ty(l), cx.typeck_results().expr_ty(r));
+                if l_ty.peel_refs().is_integral() && r_ty.peel_refs().is_integral() {
+                    match op.node {
+                        hir::BinOpKind::Div | hir::BinOpKind::Rem => match &r.kind {
+                            hir::ExprKind::Lit(_lit) => (),
+                            hir::ExprKind::Unary(hir::UnOp::Neg, expr) => {
+                                if let hir::ExprKind::Lit(lit) = &expr.kind {
+                                    if let rustc_ast::ast::LitKind::Int(1, _) = lit.node {
+                                        span_lint(cx, INTEGER_ARITHMETIC, expr.span, "integer arithmetic detected");
+                                        self.expr_span = Some(expr.span);
+                                    }
+                                }
+                            },
+                            _ => {
+                                span_lint(cx, INTEGER_ARITHMETIC, expr.span, "integer arithmetic detected");
+                                self.expr_span = Some(expr.span);
+                            },
+                        },
+                        _ => {
+                            span_lint(cx, INTEGER_ARITHMETIC, expr.span, "integer arithmetic detected");
+                            self.expr_span = Some(expr.span);
+                        },
+                    }
+                } else if r_ty.peel_refs().is_floating_point() && r_ty.peel_refs().is_floating_point() {
+                    span_lint(cx, FLOAT_ARITHMETIC, expr.span, "floating-point arithmetic detected");
+                    self.expr_span = Some(expr.span);
+                }
+            },
+            hir::ExprKind::Unary(hir::UnOp::Neg, arg) => {
+                let ty = cx.typeck_results().expr_ty(arg);
+                if constant_simple(cx, cx.typeck_results(), expr).is_none() {
+                    if ty.is_integral() {
+                        span_lint(cx, INTEGER_ARITHMETIC, expr.span, "integer arithmetic detected");
+                        self.expr_span = Some(expr.span);
+                    } else if ty.is_floating_point() {
+                        span_lint(cx, FLOAT_ARITHMETIC, expr.span, "floating-point arithmetic detected");
+                        self.expr_span = Some(expr.span);
+                    }
+                }
+            },
+            _ => (),
+        }
+    }
+
+    fn check_expr_post(&mut self, _: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
+        if Some(expr.span) == self.expr_span {
+            self.expr_span = None;
+        }
+    }
+
+    fn check_body(&mut self, cx: &LateContext<'_>, body: &hir::Body<'_>) {
+        let body_owner = cx.tcx.hir().body_owner_def_id(body.id());
+
+        match cx.tcx.hir().body_owner_kind(body_owner) {
+            hir::BodyOwnerKind::Static(_) | hir::BodyOwnerKind::Const => {
+                let body_span = cx.tcx.def_span(body_owner);
+
+                if let Some(span) = self.const_span {
+                    if span.contains(body_span) {
+                        return;
+                    }
+                }
+                self.const_span = Some(body_span);
+            },
+            hir::BodyOwnerKind::Fn | hir::BodyOwnerKind::Closure => (),
+        }
+    }
+
+    fn check_body_post(&mut self, cx: &LateContext<'_>, body: &hir::Body<'_>) {
+        let body_owner = cx.tcx.hir().body_owner(body.id());
+        let body_span = cx.tcx.hir().span(body_owner);
+
+        if let Some(span) = self.const_span {
+            if span.contains(body_span) {
+                return;
+            }
+        }
+        self.const_span = None;
+    }
+}