Merge commit '0eff589afc83e21a03a168497bbab6b4dfbb4ef6' into clippyup

[rust.git] / clippy_lints / src / casts / cast_possible_truncation.rs

diff --git a/clippy_lints/src/casts/cast_possible_truncation.rs b/clippy_lints/src/casts/cast_possible_truncation.rs
index 833ad122e0d4e20c46ae07f32c94157a4120f218..4af412ccaf35d7d0946429c5b997f9ae7081792e 100644 (file)
--- a/clippy_lints/src/casts/cast_possible_truncation.rs
+++ b/clippy_lints/src/casts/cast_possible_truncation.rs
@@ -1,15 +1,88 @@
+use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::span_lint;
+use clippy_utils::expr_or_init;
 use clippy_utils::ty::is_isize_or_usize;
-use rustc_hir::Expr;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
 use rustc_lint::LateContext;
 use rustc_middle::ty::{self, FloatTy, Ty};
 
 use super::{utils, CAST_POSSIBLE_TRUNCATION};
 
-pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+fn constant_int(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
+    if let Some((Constant::Int(c), _)) = constant(cx, cx.typeck_results(), expr) {
+        Some(c)
+    } else {
+        None
+    }
+}
+
+fn get_constant_bits(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u64> {
+    constant_int(cx, expr).map(|c| u64::from(128 - c.leading_zeros()))
+}
+
+fn apply_reductions(cx: &LateContext<'_>, nbits: u64, expr: &Expr<'_>, signed: bool) -> u64 {
+    match expr_or_init(cx, expr).kind {
+        ExprKind::Cast(inner, _) => apply_reductions(cx, nbits, inner, signed),
+        ExprKind::Block(block, _) => block.expr.map_or(nbits, |e| apply_reductions(cx, nbits, e, signed)),
+        ExprKind::Binary(op, left, right) => match op.node {
+            BinOpKind::Div => {
+                apply_reductions(cx, nbits, left, signed)
+                    - (if signed {
+                        0 // let's be conservative here
+                    } else {
+                        // by dividing by 1, we remove 0 bits, etc.
+                        get_constant_bits(cx, right).map_or(0, |b| b.saturating_sub(1))
+                    })
+            },
+            BinOpKind::Rem | BinOpKind::BitAnd => get_constant_bits(cx, right)
+                .unwrap_or(u64::max_value())
+                .min(apply_reductions(cx, nbits, left, signed)),
+            BinOpKind::Shr => {
+                apply_reductions(cx, nbits, left, signed)
+                    - constant_int(cx, right).map_or(0, |s| u64::try_from(s).expect("shift too high"))
+            },
+            _ => nbits,
+        },
+        ExprKind::MethodCall(method, _, [left, right], _) => {
+            if signed {
+                return nbits;
+            }
+            let max_bits = if method.ident.as_str() == "min" {
+                get_constant_bits(cx, right)
+            } else {
+                None
+            };
+            apply_reductions(cx, nbits, left, signed).min(max_bits.unwrap_or(u64::max_value()))
+        },
+        ExprKind::MethodCall(method, _, [_, lo, hi], _) => {
+            if method.ident.as_str() == "clamp" {
+                //FIXME: make this a diagnostic item
+                if let (Some(lo_bits), Some(hi_bits)) = (get_constant_bits(cx, lo), get_constant_bits(cx, hi)) {
+                    return lo_bits.max(hi_bits);
+                }
+            }
+            nbits
+        },
+        ExprKind::MethodCall(method, _, [_value], _) => {
+            if method.ident.name.as_str() == "signum" {
+                0 // do not lint if cast comes from a `signum` function
+            } else {
+                nbits
+            }
+        },
+        _ => nbits,
+    }
+}
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
     let msg = match (cast_from.is_integral(), cast_to.is_integral()) {
         (true, true) => {
-            let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
+            let from_nbits = apply_reductions(
+                cx,
+                utils::int_ty_to_nbits(cast_from, cx.tcx),
+                cast_expr,
+                cast_from.is_signed(),
+            );
             let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
 
             let (should_lint, suffix) = match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {