feat(missing_asserts_for_indexing): support comparing to const values

andjsrk · andjsrk · commit 541f1f43712c · 2025-12-15T06:35:09.000+09:00
diff --git a/clippy_lints/src/missing_asserts_for_indexing.rs b/clippy_lints/src/missing_asserts_for_indexing.rs
@@ -2,6 +2,7 @@ use std::mem;
 use std::ops::ControlFlow;
 
 use clippy_utils::comparisons::{Rel, normalize_comparison};
+use clippy_utils::consts::{ConstEvalCtxt, Constant};
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::higher::{If, Range};
 use clippy_utils::macros::{find_assert_eq_args, first_node_macro_backtrace, root_macro_call};
@@ -91,35 +92,113 @@ enum LengthComparison {
     /// `v.len() == 5`
     LengthEqualInt,
 }
+#[derive(Copy, Clone, Debug)]
+struct EvaluatedIntExpr<'hir> {
+    expr: &'hir Expr<'hir>,
+    value: usize,
+}
+#[derive(Copy, Clone, Debug)]
+enum AssertionSide<'hir> {
+    /// `v.len()` in `v.len() > 5`
+    SliceLen {
+        /// `v` in `v.len()`
+        slice: &'hir Expr<'hir>,
+    },
+    /// `5` in `v.len() > 5`
+    AssertedLen(EvaluatedIntExpr<'hir>),
+}
+impl<'hir> AssertionSide<'hir> {
+    pub fn slice_len_from_expr(cx: &LateContext<'_>, expr: &'hir Expr<'hir>) -> Option<Self> {
+        if let ExprKind::MethodCall(method, recv, [], _) = expr.kind
+            // checking method name first rather than receiver's type could improve performance
+            && method.ident.name == sym::len
+            && cx.typeck_results().expr_ty_adjusted(recv).peel_refs().is_slice()
+        {
+            Some(Self::SliceLen { slice: recv })
+        } else {
+            None
+        }
+    }
+    pub fn asserted_len_from_expr(cx: &LateContext<'_>, expr: &'hir Expr<'hir>) -> Option<Self> {
+        if let ExprKind::Lit(Spanned { node, .. }) = expr.kind {
+            // cases like `b'A'` or `5.0` would be extremely rare so
+            // ignore those and consider only integers
+            if let LitKind::Int(Pu128(x), _) = node {
+                // integer literals
+                Some(Self::AssertedLen(EvaluatedIntExpr {
+                    expr,
+                    value: x as usize,
+                }))
+            } else {
+                None
+            }
+        } else if let Some(Constant::Int(x)) = ConstEvalCtxt::new(cx).eval(expr) {
+            Some(Self::AssertedLen(EvaluatedIntExpr {
+                expr,
+                value: x as usize,
+            }))
+        } else {
+            None
+        }
+    }
+}
 
 /// Extracts parts out of a length comparison expression.
 ///
 /// E.g. for `v.len() > 5` this returns `Some((LengthComparison::IntLessThanLength, 5, v.len()))`
 fn len_comparison<'hir>(
+    cx: &LateContext<'_>,
     bin_op: BinOpKind,
-    left: &'hir Expr<'hir>,
-    right: &'hir Expr<'hir>,
-) -> Option<(LengthComparison, usize, &'hir Expr<'hir>)> {
-    macro_rules! int_lit_pat {
-        ($id:ident) => {
-            ExprKind::Lit(Spanned {
-                node: LitKind::Int(Pu128($id), _),
-                ..
-            })
-        };
-    }
+    left_expr: &'hir Expr<'hir>,
+    right_expr: &'hir Expr<'hir>,
+) -> Option<(LengthComparison, EvaluatedIntExpr<'hir>, &'hir Expr<'hir>)> {
+    type Side<'hir> = AssertionSide<'hir>;
 
     // normalize comparison, `v.len() > 4` becomes `4 < v.len()`
     // this simplifies the logic a bit
-    let (op, left, right) = normalize_comparison(bin_op, left, right)?;
-    match (op, left.kind, right.kind) {
-        (Rel::Lt, int_lit_pat!(left), _) => Some((LengthComparison::IntLessThanLength, left as usize, right)),
-        (Rel::Lt, _, int_lit_pat!(right)) => Some((LengthComparison::LengthLessThanInt, right as usize, left)),
-        (Rel::Le, int_lit_pat!(left), _) => Some((LengthComparison::IntLessThanOrEqualLength, left as usize, right)),
-        (Rel::Le, _, int_lit_pat!(right)) => Some((LengthComparison::LengthLessThanOrEqualInt, right as usize, left)),
-        (Rel::Eq, int_lit_pat!(left), _) => Some((LengthComparison::LengthEqualInt, left as usize, right)),
-        (Rel::Eq, _, int_lit_pat!(right)) => Some((LengthComparison::LengthEqualInt, right as usize, left)),
-        _ => None,
+    let (op, left_expr, right_expr) = normalize_comparison(bin_op, left_expr, right_expr)?;
+
+    // sniff operands as cheap as possible
+    // eliminate possibility of both sides being `v.len()` variant
+    let (left, right) = match AssertionSide::slice_len_from_expr(cx, left_expr) {
+        Some(left) => (left, AssertionSide::asserted_len_from_expr(cx, right_expr)?),
+        None => (
+            AssertionSide::asserted_len_from_expr(cx, left_expr)?,
+            AssertionSide::slice_len_from_expr(cx, right_expr)?,
+        ),
+    };
+    let (swapped, asserted_len, slice) = match (left, right) {
+        // `A > B` (e.g. `5 > 4`)
+        | (Side::AssertedLen(_), Side::AssertedLen(_))
+        // `v.len() > w.len()`
+        | (Side::SliceLen { .. }, Side::SliceLen { .. }) => return None,
+        (Side::AssertedLen(asserted_len), Side::SliceLen { slice }) => {
+            (false, asserted_len, slice)
+        },
+        (Side::SliceLen { slice }, Side::AssertedLen(asserted_len)) => {
+            (true, asserted_len, slice)
+        },
+    };
+
+    match op {
+        Rel::Lt => {
+            let cmp = if swapped {
+                LengthComparison::LengthLessThanInt
+            } else {
+                LengthComparison::IntLessThanLength
+            };
+            Some((cmp, asserted_len, slice))
+        },
+        Rel::Le => {
+            let cmp = if swapped {
+                LengthComparison::LengthLessThanOrEqualInt
+            } else {
+                LengthComparison::IntLessThanOrEqualLength
+            };
+            Some((cmp, asserted_len, slice))
+        },
+        Rel::Eq => Some((LengthComparison::LengthEqualInt, asserted_len, slice)),
+        Rel::Ne => None,
     }
 }
 
@@ -132,15 +211,15 @@ fn len_comparison<'hir>(
 fn assert_len_expr<'hir>(
     cx: &LateContext<'_>,
     expr: &'hir Expr<'hir>,
-) -> Option<(LengthComparison, usize, &'hir Expr<'hir>, Symbol)> {
-    let ((cmp, asserted_len, slice_len), macro_call) = if let Some(If { cond, then, .. }) = If::hir(expr)
+) -> Option<(LengthComparison, EvaluatedIntExpr<'hir>, &'hir Expr<'hir>, Symbol)> {
+    let ((cmp, asserted_len, slice), macro_call) = if let Some(If { cond, then, .. }) = If::hir(expr)
         && let ExprKind::Unary(UnOp::Not, condition) = &cond.kind
         && let ExprKind::Binary(bin_op, left, right) = &condition.kind
         // check if `then` block has a never type expression
         && let ExprKind::Block(Block { expr: Some(then_expr), .. }, _) = then.kind
         && cx.typeck_results().expr_ty(then_expr).is_never()
     {
-        (len_comparison(bin_op.node, left, right)?, sym::assert_macro)
+        (len_comparison(cx, bin_op.node, left, right)?, sym::assert_macro)
     } else if let Some((macro_call, bin_op)) = first_node_macro_backtrace(cx, expr).find_map(|macro_call| {
         match cx.tcx.get_diagnostic_name(macro_call.def_id) {
             Some(sym::assert_eq_macro) => Some((macro_call, BinOpKind::Eq)),
@@ -150,7 +229,7 @@ fn assert_len_expr<'hir>(
     }) && let Some((left, right, _)) = find_assert_eq_args(cx, expr, macro_call.expn)
     {
         (
-            len_comparison(bin_op, left, right)?,
+            len_comparison(cx, bin_op, left, right)?,
             root_macro_call(expr.span)
                 .and_then(|macro_call| cx.tcx.get_diagnostic_name(macro_call.def_id))
                 .unwrap_or(sym::assert_macro),
@@ -159,21 +238,14 @@ fn assert_len_expr<'hir>(
         return None;
     };
 
-    if let ExprKind::MethodCall(method, recv, [], _) = &slice_len.kind
-        && cx.typeck_results().expr_ty_adjusted(recv).peel_refs().is_slice()
-        && method.ident.name == sym::len
-    {
-        Some((cmp, asserted_len, recv, macro_call))
-    } else {
-        None
-    }
+    Some((cmp, asserted_len, slice, macro_call))
 }
 
 #[derive(Debug)]
 enum IndexEntry<'hir> {
     /// `assert!` without any indexing (so far)
     StrayAssert {
-        asserted_len: usize,
+        asserted_len: EvaluatedIntExpr<'hir>,
         comparison: LengthComparison,
         assert_span: Span,
         slice: &'hir Expr<'hir>,
@@ -186,7 +258,7 @@ enum IndexEntry<'hir> {
     AssertWithIndex {
         highest_index: usize,
         is_first_highest: bool,
-        asserted_len: usize,
+        asserted_len: EvaluatedIntExpr<'hir>,
         assert_span: Span,
         slice: &'hir Expr<'hir>,
         indexes: Vec<Span>,
@@ -367,22 +439,29 @@ fn report_indexes(cx: &LateContext<'_>, map: UnindexMap<u64, Vec<IndexEntry<'_>>
                             Some(format!("assert!({slice_str}.len() > {highest_index})",))
                         },
                         // `5 < v.len()` == `v.len() > 5`
-                        LengthComparison::IntLessThanLength if asserted_len < highest_index => {
+                        LengthComparison::IntLessThanLength if asserted_len.value < highest_index => {
                             Some(format!("assert!({slice_str}.len() > {highest_index})",))
                         },
                         // `5 <= v.len() == `v.len() >= 5`
-                        LengthComparison::IntLessThanOrEqualLength if asserted_len <= highest_index => {
-                            Some(format!("assert!({slice_str}.len() > {highest_index})",))
+                        LengthComparison::IntLessThanOrEqualLength if asserted_len.value == highest_index => {
+                            let asserted_len_str =
+                                snippet_with_applicability(cx, asserted_len.expr.span, "_", &mut app);
+                            Some(format!("assert!({slice_str}.len() > {asserted_len_str})",))
+                        },
+                        LengthComparison::IntLessThanOrEqualLength if asserted_len.value < highest_index => {
+                            Some(format!("assert!({slice_str}.len() >= {})", highest_index + 1))
                         },
                         // `highest_index` here is rather a length, so we need to add 1 to it
-                        LengthComparison::LengthEqualInt if asserted_len < highest_index + 1 => match macro_call {
-                            sym::assert_eq_macro => {
-                                Some(format!("assert_eq!({slice_str}.len(), {})", highest_index + 1))
-                            },
-                            sym::debug_assert_eq_macro => {
-                                Some(format!("debug_assert_eq!({slice_str}.len(), {})", highest_index + 1))
-                            },
-                            _ => Some(format!("assert!({slice_str}.len() == {})", highest_index + 1)),
+                        LengthComparison::LengthEqualInt if asserted_len.value < highest_index + 1 => {
+                            match macro_call {
+                                sym::assert_eq_macro => {
+                                    Some(format!("assert_eq!({slice_str}.len(), {})", highest_index + 1))
+                                },
+                                sym::debug_assert_eq_macro => {
+                                    Some(format!("debug_assert_eq!({slice_str}.len(), {})", highest_index + 1))
+                                },
+                                _ => Some(format!("assert!({slice_str}.len() == {})", highest_index + 1)),
+                            }
                         },
                         _ => None,
                     };
diff --git a/tests/ui/missing_asserts_for_indexing.fixed b/tests/ui/missing_asserts_for_indexing.fixed
@@ -180,4 +180,24 @@ mod issue15988 {
     }
 }
 
+fn assert_cmp_to_const(v1: &[u8], v2: &[u8], v3: &[u8], v4: &[u8]) {
+    const N: usize = 2;
+
+    assert!(v1.len() >= N);
+    assert!(v2.len() > N);
+    assert!(v3.len() >= 4);
+    assert!(v4.len() > 3);
+
+    let _ = v1[0] + v1[1];
+
+    let _ = v2[0] + v2[1] + v2[2];
+    //~^ missing_asserts_for_indexing
+
+    let _ = v3[0] + v3[1] + v3[2] + v3[3];
+    //~^ missing_asserts_for_indexing
+
+    let _ = v4[0] + v4[1] + v4[2] + v4[3];
+    //~^ missing_asserts_for_indexing
+}
+
 fn main() {}
diff --git a/tests/ui/missing_asserts_for_indexing.rs b/tests/ui/missing_asserts_for_indexing.rs
@@ -180,4 +180,24 @@ mod issue15988 {
     }
 }
 
+fn assert_cmp_to_const(v1: &[u8], v2: &[u8], v3: &[u8], v4: &[u8]) {
+    const N: usize = 2;
+
+    assert!(v1.len() >= N);
+    assert!(v2.len() >= N);
+    assert!(v3.len() >= N);
+    assert!(v4.len() > N);
+
+    let _ = v1[0] + v1[1];
+
+    let _ = v2[0] + v2[1] + v2[2];
+    //~^ missing_asserts_for_indexing
+
+    let _ = v3[0] + v3[1] + v3[2] + v3[3];
+    //~^ missing_asserts_for_indexing
+
+    let _ = v4[0] + v4[1] + v4[2] + v4[3];
+    //~^ missing_asserts_for_indexing
+}
+
 fn main() {}
diff --git a/tests/ui/missing_asserts_for_indexing.stderr b/tests/ui/missing_asserts_for_indexing.stderr
@@ -187,5 +187,41 @@ LL -         debug_assert_eq!(v.len(), 2);
 LL +         debug_assert_eq!(v.len(), 3);
    |
 
-error: aborting due to 15 previous errors
+error: indexing into a slice multiple times with an `assert` that does not cover the highest index
+  --> tests/ui/missing_asserts_for_indexing.rs:193:13
+   |
+LL |     let _ = v2[0] + v2[1] + v2[2];
+   |             ^^^^^   ^^^^^   ^^^^^
+   |
+help: provide the highest index that is indexed with
+   |
+LL -     assert!(v2.len() >= N);
+LL +     assert!(v2.len() > N);
+   |
+
+error: indexing into a slice multiple times with an `assert` that does not cover the highest index
+  --> tests/ui/missing_asserts_for_indexing.rs:196:13
+   |
+LL |     let _ = v3[0] + v3[1] + v3[2] + v3[3];
+   |             ^^^^^   ^^^^^   ^^^^^   ^^^^^
+   |
+help: provide the highest index that is indexed with
+   |
+LL -     assert!(v3.len() >= N);
+LL +     assert!(v3.len() >= 4);
+   |
+
+error: indexing into a slice multiple times with an `assert` that does not cover the highest index
+  --> tests/ui/missing_asserts_for_indexing.rs:199:13
+   |
+LL |     let _ = v4[0] + v4[1] + v4[2] + v4[3];
+   |             ^^^^^   ^^^^^   ^^^^^   ^^^^^
+   |
+help: provide the highest index that is indexed with
+   |
+LL -     assert!(v4.len() > N);
+LL +     assert!(v4.len() > 3);
+   |
+
+error: aborting due to 18 previous errors
 
