cast_abs_to_unsigned: do not remove cast if it's required

4 files changed, 157 insertions, 23 deletions

diff --git a/clippy_lints/src/casts/cast_abs_to_unsigned.rs b/clippy_lints/src/casts/cast_abs_to_unsigned.rs
index 6bac6bf83f8..64ea326b75a 100644
--- a/clippy_lints/src/casts/cast_abs_to_unsigned.rs
+++ b/clippy_lints/src/casts/cast_abs_to_unsigned.rs
@@ -1,11 +1,10 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{meets_msrv, msrvs};
-use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::LateContext;
-use rustc_middle::ty::Ty;
+use rustc_middle::ty::{self, Ty};
 use rustc_semver::RustcVersion;
 
 use super::CAST_ABS_TO_UNSIGNED;
@@ -18,25 +17,28 @@ pub(super) fn check(
     cast_to: Ty<'_>,
     msrv: Option<RustcVersion>,
 ) {
-    if_chain! {
-        if meets_msrv(msrv, msrvs::UNSIGNED_ABS);
-        if cast_from.is_integral();
-        if cast_to.is_integral();
-        if cast_from.is_signed();
-        if !cast_to.is_signed();
-        if let ExprKind::MethodCall(method_path, args, _) = cast_expr.kind;
-        if let method_name = method_path.ident.name.as_str();
-        if method_name == "abs";
-        then {
-            span_lint_and_sugg(
-                cx,
-                CAST_ABS_TO_UNSIGNED,
-                expr.span,
-                &format!("casting the result of `{}::{}()` to {}", cast_from, method_name, cast_to),
-                "replace with",
-                format!("{}.unsigned_abs()", Sugg::hir(cx, &args[0], "..")),
-                Applicability::MachineApplicable,
-            );
-        }
+    if meets_msrv(msrv, msrvs::UNSIGNED_ABS)
+        && let ty::Int(from) = cast_from.kind()
+        && let ty::Uint(to) = cast_to.kind()
+        && let ExprKind::MethodCall(method_path, args, _) = cast_expr.kind
+        && method_path.ident.name.as_str() == "abs"
+    {
+        let span = if from.bit_width() == to.bit_width() {
+            expr.span
+        } else {
+            // if the result of `.unsigned_abs` would be a different type, keep the cast
+            // e.g. `i64 -> usize`, `i16 -> u8`
+            cast_expr.span
+        };
+
+        span_lint_and_sugg(
+            cx,
+            CAST_ABS_TO_UNSIGNED,
+            span,
+            &format!("casting the result of `{cast_from}::abs()` to {cast_to}"),
+            "replace with",
+            format!("{}.unsigned_abs()", Sugg::hir(cx, &args[0], "..")),
+            Applicability::MachineApplicable,
+        );
     }
 }
diff --git a/tests/ui/cast_abs_to_unsigned.fixed b/tests/ui/cast_abs_to_unsigned.fixed
index 4ec2465be06..a68b32b097e 100644
--- a/tests/ui/cast_abs_to_unsigned.fixed
+++ b/tests/ui/cast_abs_to_unsigned.fixed
@@ -5,4 +5,25 @@ fn main() {
     let x: i32 = -42;
     let y: u32 = x.unsigned_abs();
     println!("The absolute value of {} is {}", x, y);
+
+    let a: i32 = -3;
+    let _: usize = a.unsigned_abs() as usize;
+    let _: usize = a.unsigned_abs() as _;
+    let _ = a.unsigned_abs() as usize;
+
+    let a: i64 = -3;
+    let _ = a.unsigned_abs() as usize;
+    let _ = a.unsigned_abs() as u8;
+    let _ = a.unsigned_abs() as u16;
+    let _ = a.unsigned_abs() as u32;
+    let _ = a.unsigned_abs();
+    let _ = a.unsigned_abs() as u128;
+
+    let a: isize = -3;
+    let _ = a.unsigned_abs();
+    let _ = a.unsigned_abs() as u8;
+    let _ = a.unsigned_abs() as u16;
+    let _ = a.unsigned_abs() as u32;
+    let _ = a.unsigned_abs() as u64;
+    let _ = a.unsigned_abs() as u128;
 }
diff --git a/tests/ui/cast_abs_to_unsigned.rs b/tests/ui/cast_abs_to_unsigned.rs
index 59b9c8c3678..110fbc6c2df 100644
--- a/tests/ui/cast_abs_to_unsigned.rs
+++ b/tests/ui/cast_abs_to_unsigned.rs
@@ -5,4 +5,25 @@ fn main() {
     let x: i32 = -42;
     let y: u32 = x.abs() as u32;
     println!("The absolute value of {} is {}", x, y);
+
+    let a: i32 = -3;
+    let _: usize = a.abs() as usize;
+    let _: usize = a.abs() as _;
+    let _ = a.abs() as usize;
+
+    let a: i64 = -3;
+    let _ = a.abs() as usize;
+    let _ = a.abs() as u8;
+    let _ = a.abs() as u16;
+    let _ = a.abs() as u32;
+    let _ = a.abs() as u64;
+    let _ = a.abs() as u128;
+
+    let a: isize = -3;
+    let _ = a.abs() as usize;
+    let _ = a.abs() as u8;
+    let _ = a.abs() as u16;
+    let _ = a.abs() as u32;
+    let _ = a.abs() as u64;
+    let _ = a.abs() as u128;
 }
diff --git a/tests/ui/cast_abs_to_unsigned.stderr b/tests/ui/cast_abs_to_unsigned.stderr
index eb12857357a..02c24e10659 100644
--- a/tests/ui/cast_abs_to_unsigned.stderr
+++ b/tests/ui/cast_abs_to_unsigned.stderr
@@ -6,5 +6,95 @@ LL |     let y: u32 = x.abs() as u32;
    |
    = note: `-D clippy::cast-abs-to-unsigned` implied by `-D warnings`
 
-error: aborting due to previous error
+error: casting the result of `i32::abs()` to usize
+  --> $DIR/cast_abs_to_unsigned.rs:10:20
+   |
+LL |     let _: usize = a.abs() as usize;
+   |                    ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `i32::abs()` to usize
+  --> $DIR/cast_abs_to_unsigned.rs:11:20
+   |
+LL |     let _: usize = a.abs() as _;
+   |                    ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `i32::abs()` to usize
+  --> $DIR/cast_abs_to_unsigned.rs:12:13
+   |
+LL |     let _ = a.abs() as usize;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `i64::abs()` to usize
+  --> $DIR/cast_abs_to_unsigned.rs:15:13
+   |
+LL |     let _ = a.abs() as usize;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `i64::abs()` to u8
+  --> $DIR/cast_abs_to_unsigned.rs:16:13
+   |
+LL |     let _ = a.abs() as u8;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `i64::abs()` to u16
+  --> $DIR/cast_abs_to_unsigned.rs:17:13
+   |
+LL |     let _ = a.abs() as u16;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `i64::abs()` to u32
+  --> $DIR/cast_abs_to_unsigned.rs:18:13
+   |
+LL |     let _ = a.abs() as u32;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `i64::abs()` to u64
+  --> $DIR/cast_abs_to_unsigned.rs:19:13
+   |
+LL |     let _ = a.abs() as u64;
+   |             ^^^^^^^^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `i64::abs()` to u128
+  --> $DIR/cast_abs_to_unsigned.rs:20:13
+   |
+LL |     let _ = a.abs() as u128;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `isize::abs()` to usize
+  --> $DIR/cast_abs_to_unsigned.rs:23:13
+   |
+LL |     let _ = a.abs() as usize;
+   |             ^^^^^^^^^^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `isize::abs()` to u8
+  --> $DIR/cast_abs_to_unsigned.rs:24:13
+   |
+LL |     let _ = a.abs() as u8;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `isize::abs()` to u16
+  --> $DIR/cast_abs_to_unsigned.rs:25:13
+   |
+LL |     let _ = a.abs() as u16;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `isize::abs()` to u32
+  --> $DIR/cast_abs_to_unsigned.rs:26:13
+   |
+LL |     let _ = a.abs() as u32;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `isize::abs()` to u64
+  --> $DIR/cast_abs_to_unsigned.rs:27:13
+   |
+LL |     let _ = a.abs() as u64;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: casting the result of `isize::abs()` to u128
+  --> $DIR/cast_abs_to_unsigned.rs:28:13
+   |
+LL |     let _ = a.abs() as u128;
+   |             ^^^^^^^ help: replace with: `a.unsigned_abs()`
+
+error: aborting due to 16 previous errors