Auto merge of rust-lang#4883 - krishna-veerareddy:issue-4818-cast-sig…

…n-loss-false-positive, r=flip1995

Fix false positive with cast_sign_loss lint

`cast_sign_loss` lint incorrectly suggests that the result of `checked_abs`, `rem_euclid` and `checked_rem_euclid` cannot be casted to an unsigned integer without loss.

Fixes rust-lang#4818 rust-lang#4764 rust-lang#4743

changelog: Fix false positives in `cast_sign_loss` lint

clippy_lints/src/types.rs

@@ -26,8 +26,9 @@ use crate::consts::{constant, Constant};
 use crate::utils::paths;
 use crate::utils::{
     clip, comparisons, differing_macro_contexts, higher, in_constant, int_bits, last_path_segment, match_def_path,
-    match_path, multispan_sugg, qpath_res, same_tys, sext, snippet, snippet_opt, snippet_with_applicability,
-    snippet_with_macro_callsite, span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, unsext,
+    match_path, method_chain_args, multispan_sugg, qpath_res, same_tys, sext, snippet, snippet_opt,
+    snippet_with_applicability, snippet_with_macro_callsite, span_help_and_lint, span_lint, span_lint_and_sugg,
+    span_lint_and_then, unsext,
 };
 
 declare_clippy_lint! {
@@ -1021,14 +1022,22 @@ fn check_loss_of_sign(cx: &LateContext<'_, '_>, expr: &Expr, op: &Expr, cast_fro
         }
     }
 
-    // don't lint for the result of `abs`
-    // `abs` is an inherent impl of `i{N}`, so a method call with ident `abs` will always
-    // resolve to that spesific method
-    if_chain! {
-        if let ExprKind::MethodCall(ref path, _, _) = op.kind;
-        if path.ident.name.as_str() == "abs";
-        then {
-            return
+    // don't lint for the result of methods that always return non-negative values
+    if let ExprKind::MethodCall(ref path, _, _) = op.kind {
+        let mut method_name = path.ident.name.as_str();
+        let whitelisted_methods = ["abs", "checked_abs", "rem_euclid", "checked_rem_euclid"];
+
+        if_chain! {
+            if method_name == "unwrap";
+            if let Some(arglist) = method_chain_args(op, &["unwrap"]);
+            if let ExprKind::MethodCall(ref inner_path, _, _) = &arglist[0][0].kind;
+            then {
+                method_name = inner_path.ident.name.as_str();
+            }
+        }
+
+        if whitelisted_methods.iter().any(|&name| method_name == name) {
+            return;
         }
     }
 

tests/ui/cast.rs

@@ -42,9 +42,54 @@ fn main() {
     i32::max_value() as u32;
     i64::max_value() as u64;
     i128::max_value() as u128;
+
     (-1i8).abs() as u8;
     (-1i16).abs() as u16;
     (-1i32).abs() as u32;
     (-1i64).abs() as u64;
     (-1isize).abs() as usize;
+
+    (-1i8).checked_abs().unwrap() as u8;
+    (-1i16).checked_abs().unwrap() as u16;
+    (-1i32).checked_abs().unwrap() as u32;
+    (-1i64).checked_abs().unwrap() as u64;
+    (-1isize).checked_abs().unwrap() as usize;
+
+    (-1i8).rem_euclid(1i8) as u8;
+    (-1i8).rem_euclid(1i8) as u16;
+    (-1i16).rem_euclid(1i16) as u16;
+    (-1i16).rem_euclid(1i16) as u32;
+    (-1i32).rem_euclid(1i32) as u32;
+    (-1i32).rem_euclid(1i32) as u64;
+    (-1i64).rem_euclid(1i64) as u64;
+    (-1i64).rem_euclid(1i64) as u128;
+    (-1isize).rem_euclid(1isize) as usize;
+    (1i8).rem_euclid(-1i8) as u8;
+    (1i8).rem_euclid(-1i8) as u16;
+    (1i16).rem_euclid(-1i16) as u16;
+    (1i16).rem_euclid(-1i16) as u32;
+    (1i32).rem_euclid(-1i32) as u32;
+    (1i32).rem_euclid(-1i32) as u64;
+    (1i64).rem_euclid(-1i64) as u64;
+    (1i64).rem_euclid(-1i64) as u128;
+    (1isize).rem_euclid(-1isize) as usize;
+
+    (-1i8).checked_rem_euclid(1i8).unwrap() as u8;
+    (-1i8).checked_rem_euclid(1i8).unwrap() as u16;
+    (-1i16).checked_rem_euclid(1i16).unwrap() as u16;
+    (-1i16).checked_rem_euclid(1i16).unwrap() as u32;
+    (-1i32).checked_rem_euclid(1i32).unwrap() as u32;
+    (-1i32).checked_rem_euclid(1i32).unwrap() as u64;
+    (-1i64).checked_rem_euclid(1i64).unwrap() as u64;
+    (-1i64).checked_rem_euclid(1i64).unwrap() as u128;
+    (-1isize).checked_rem_euclid(1isize).unwrap() as usize;
+    (1i8).checked_rem_euclid(-1i8).unwrap() as u8;
+    (1i8).checked_rem_euclid(-1i8).unwrap() as u16;
+    (1i16).checked_rem_euclid(-1i16).unwrap() as u16;
+    (1i16).checked_rem_euclid(-1i16).unwrap() as u32;
+    (1i32).checked_rem_euclid(-1i32).unwrap() as u32;
+    (1i32).checked_rem_euclid(-1i32).unwrap() as u64;
+    (1i64).checked_rem_euclid(-1i64).unwrap() as u64;
+    (1i64).checked_rem_euclid(-1i64).unwrap() as u128;
+    (1isize).checked_rem_euclid(-1isize).unwrap() as usize;
 }