use is_integer_const, add split_off on sym.rs

Author: sebhernandezr

clippy_lints/src/unnecessary_split_off.rs

@@ -1,5 +1,5 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::sym;
+use clippy_utils::{is_integer_const, sym, ty};
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
@@ -30,15 +30,14 @@ declare_lint_pass!(UnnecessarySplitOff => [UNNECESSARY_SPLIT_OFF]);
 impl<'tcx> LateLintPass<'tcx> for UnnecessarySplitOff {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
         if let ExprKind::MethodCall(path, value, args, span) = &expr.kind
-        // FIXME: sym::split_off does not exist, but this still triggers the lint to use it.
-            && path.ident.name.as_str() == "split_off"
+            && path.ident.name == sym::split_off
         {
             let ty = cx.typeck_results().expr_ty(value);
-            if clippy_utils::ty::is_type_diagnostic_item(cx, ty, sym::Vec) {
+            if ty::is_type_diagnostic_item(cx, ty, sym::Vec) {
                 let &[arg] = args else {
                     return;
                 };
-                if clippy_utils::is_integer_literal(arg, 0) || clippy_utils::is_integer_const(cx, arg, 0) {
+                if is_integer_const(cx, arg, 0) {
                     span_lint_and_sugg(
                         cx,
                         UNNECESSARY_SPLIT_OFF,

clippy_utils/src/sym.rs

@@ -307,6 +307,7 @@ generate! {
     split_at_mut,
     split_at_mut_checked,
     split_inclusive,
+    split_off,
     split_once,
     split_terminator,
     split_whitespace,

tests/ui/unnecessary_split_off.rs

@@ -7,8 +7,6 @@ impl A {
     fn split_off(&mut self, _: usize) {}
 }
 
-const ZERO: usize = 0;
-
 fn main() {
     let mut vec1 = vec![1, 2, 3];
 
@@ -17,12 +15,17 @@ fn main() {
 
     let vec3: Vec<_> = vec1.split_off(1);
 
+    const ZERO: usize = 0;
     let vec4: Vec<_> = vec1.split_off(ZERO);
     //~^ unnecessary_split_off
 
     let vec5: Vec<_> = vec1.split_off(const { 0 });
     //~^ unnecessary_split_off
 
+    let zero = 0;
+    let vec6: Vec<_> = vec1.split_off(zero);
+    //~^ unnecessary_split_off
+
     let mut a = A;
     a.split_off(0);
 }