Auto merge of #11395 - c410-f3r:let-chain, r=Manishearth

[`arithmetic_side_effects`] Fix #11393

Fix #11393

```
changelog: [`arithmetic_side_effects`]: Detect division by zero for `Wrapping` and `Saturating`
```

clippy_lints/src/operators/arithmetic_side_effects.rs

@@ -1,22 +1,18 @@
 use super::ARITHMETIC_SIDE_EFFECTS;
 use clippy_utils::consts::{constant, constant_simple, Constant};
 use clippy_utils::diagnostics::span_lint;
+use clippy_utils::ty::{match_type, type_diagnostic_name};
 use clippy_utils::{expr_or_init, is_from_proc_macro, is_lint_allowed, peel_hir_expr_refs, peel_hir_expr_unary};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::Ty;
 use rustc_session::impl_lint_pass;
 use rustc_span::source_map::{Span, Spanned};
+use rustc_span::symbol::sym;
 use rustc_span::Symbol;
 use {rustc_ast as ast, rustc_hir as hir};
 
-const HARD_CODED_ALLOWED_BINARY: &[[&str; 2]] = &[
+const HARD_CODED_ALLOWED_BINARY: &[[&str; 2]] = &[["f32", "f32"], ["f64", "f64"], ["std::string::String", "str"]];
-    ["f32", "f32"],
-    ["f64", "f64"],
-    ["std::num::Saturating", "*"],
-    ["std::num::Wrapping", "*"],
-    ["std::string::String", "str"],
-];
 const HARD_CODED_ALLOWED_UNARY: &[&str] = &["f32", "f64", "std::num::Saturating", "std::num::Wrapping"];
 const INTEGER_METHODS: &[&str] = &["saturating_div", "wrapping_div", "wrapping_rem", "wrapping_rem_euclid"];
 
@@ -86,6 +82,48 @@ impl ArithmeticSideEffects {
         self.allowed_unary.contains(ty_string_elem)
     }
 
+    /// Verifies built-in types that have specific allowed operations
+    fn has_specific_allowed_type_and_operation(
+        cx: &LateContext<'_>,
+        lhs_ty: Ty<'_>,
+        op: &Spanned<hir::BinOpKind>,
+        rhs_ty: Ty<'_>,
+    ) -> bool {
+        const SATURATING: &[&str] = &["core", "num", "saturating", "Saturating"];
+        const WRAPPING: &[&str] = &["core", "num", "wrapping", "Wrapping"];
+        let is_non_zero = |symbol: Option<Symbol>| {
+            matches!(
+                symbol,
+                Some(
+                    sym::NonZeroI128
+                        | sym::NonZeroI16
+                        | sym::NonZeroI32
+                        | sym::NonZeroI64
+                        | sym::NonZeroI8
+                        | sym::NonZeroU128
+                        | sym::NonZeroU16
+                        | sym::NonZeroU32
+                        | sym::NonZeroU64
+                        | sym::NonZeroU8
+                )
+            )
+        };
+        // If the RHS is NonZero*, then division or module by zero will never occur
+        if is_non_zero(type_diagnostic_name(cx, rhs_ty)) && let hir::BinOpKind::Div | hir::BinOpKind::Rem = op.node {
+            return true;
+        }
+        // For `Saturation` or `Wrapping` (RHS), all but division and module are allowed.
+        let is_div_or_rem = matches!(op.node, hir::BinOpKind::Div | hir::BinOpKind::Rem);
+        if (match_type(cx, rhs_ty, SATURATING) || match_type(cx, rhs_ty, WRAPPING)) && !is_div_or_rem {
+            return true;
+        }
+        // For `Saturation` or `Wrapping` (LHS), everything is allowed
+        if match_type(cx, lhs_ty, SATURATING) || match_type(cx, lhs_ty, WRAPPING) {
+            return true;
+        }
+        false
+    }
+
     // For example, 8i32 or &i64::MAX.
     fn is_integral(ty: Ty<'_>) -> bool {
         ty.peel_refs().is_integral()
@@ -147,6 +185,9 @@ impl ArithmeticSideEffects {
         if self.has_allowed_binary(lhs_ty, rhs_ty) {
             return;
         }
+        if Self::has_specific_allowed_type_and_operation(cx, lhs_ty, op, rhs_ty) {
+            return;
+        }
         let has_valid_op = if Self::is_integral(lhs_ty) && Self::is_integral(rhs_ty) {
             if let hir::BinOpKind::Shl | hir::BinOpKind::Shr = op.node {
                 // At least for integers, shifts are already handled by the CTFE

tests/ui/arithmetic_side_effects.rs

@@ -15,7 +15,7 @@
 
 extern crate proc_macro_derive;
 
-use core::num::{Saturating, Wrapping};
+use core::num::{NonZeroUsize, Saturating, Wrapping};
 
 const ONE: i32 = 1;
 const ZERO: i32 = 0;
@@ -493,4 +493,32 @@ pub fn issue_11262() {
     let _ = 2 / zero;
 }
 
+pub fn issue_11392() {
+    fn example_div(unsigned: usize, nonzero_unsigned: NonZeroUsize) -> usize {
+        unsigned / nonzero_unsigned
+    }
+
+    fn example_rem(unsigned: usize, nonzero_unsigned: NonZeroUsize) -> usize {
+        unsigned % nonzero_unsigned
+    }
+
+    let (unsigned, nonzero_unsigned) = (0, NonZeroUsize::new(1).unwrap());
+    example_div(unsigned, nonzero_unsigned);
+    example_rem(unsigned, nonzero_unsigned);
+}
+
+pub fn issue_11393() {
+    fn example_div(x: Wrapping<i32>, maybe_zero: Wrapping<i32>) -> Wrapping<i32> {
+        x / maybe_zero
+    }
+
+    fn example_rem(x: Wrapping<i32>, maybe_zero: Wrapping<i32>) -> Wrapping<i32> {
+        x % maybe_zero
+    }
+
+    let [x, maybe_zero] = [1, 0].map(Wrapping);
+    example_div(x, maybe_zero);
+    example_rem(x, maybe_zero);
+}
+
 fn main() {}

tests/ui/arithmetic_side_effects.stderr

@@ -702,5 +702,17 @@ error: arithmetic operation that can potentially result in unexpected side-effec
 LL |     10 / a
    |     ^^^^^^
 
-error: aborting due to 117 previous errors
+error: arithmetic operation that can potentially result in unexpected side-effects
+  --> $DIR/arithmetic_side_effects.rs:498:9
+   |
+LL |         unsigned / nonzero_unsigned
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: arithmetic operation that can potentially result in unexpected side-effects
+  --> $DIR/arithmetic_side_effects.rs:502:9
+   |
+LL |         unsigned % nonzero_unsigned
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 119 previous errors