chore: use multipart_suggestions for str_splitn (#13789)

This addresses #13099 for the manual_split_once test, using the
str_splitn lint.

changelog: [str_splitn]: Updated str_splitn to use multipart_suggestions
where appropriate

Author: Jarcho

clippy_lints/src/methods/str_splitn.rs

@@ -129,7 +129,7 @@ fn check_manual_split_once_indirect(
     let ctxt = expr.span.ctxt();
     let mut parents = cx.tcx.hir().parent_iter(expr.hir_id);
     if let (_, Node::LetStmt(local)) = parents.next()?
-        && let PatKind::Binding(BindingMode::MUT, iter_binding_id, iter_ident, None) = local.pat.kind
+        && let PatKind::Binding(BindingMode::MUT, iter_binding_id, _, None) = local.pat.kind
         && let (iter_stmt_id, Node::Stmt(_)) = parents.next()?
         && let (_, Node::Block(enclosing_block)) = parents.next()?
         && let mut stmts = enclosing_block
@@ -162,16 +162,20 @@ fn check_manual_split_once_indirect(
                 UnwrapKind::Unwrap => ".unwrap()",
                 UnwrapKind::QuestionMark => "?",
             };
-            diag.span_suggestion_verbose(
-                local.span,
-                format!("try `{r}split_once`"),
-                format!("let ({lhs}, {rhs}) = {self_snip}.{r}split_once({pat_snip}){unwrap};"),
+
+            // Add a multipart suggestion
+            diag.multipart_suggestion(
+                format!("replace with `{r}split_once`"),
+                vec![
+                    (
+                        local.span,
+                        format!("let ({lhs}, {rhs}) = {self_snip}.{r}split_once({pat_snip}){unwrap};"),
+                    ),
+                    (first.span, String::new()),  // Remove the first usage
+                    (second.span, String::new()), // Remove the second usage
+                ],
                 app,
             );
-
-            let remove_msg = format!("remove the `{iter_ident}` usages");
-            diag.span_suggestion(first.span, remove_msg.clone(), "", app);
-            diag.span_suggestion(second.span, remove_msg, "", app);
         });
     }
 

tests/ui/manual_split_once.fixed

@@ -0,0 +1,144 @@
+#![warn(clippy::manual_split_once)]
+#![allow(unused, clippy::iter_skip_next, clippy::iter_nth_zero)]
+
+extern crate itertools;
+
+#[allow(unused_imports)]
+use itertools::Itertools;
+
+fn main() {
+    let _ = "key=value".splitn(2, '=').nth(2);
+    let _ = "key=value".split_once('=').unwrap().1;
+    let _ = "key=value".split_once('=').unwrap().1;
+    let (_, _) = "key=value".split_once('=').unwrap();
+
+    let s = String::from("key=value");
+    let _ = s.split_once('=').unwrap().1;
+
+    let s = Box::<str>::from("key=value");
+    let _ = s.split_once('=').unwrap().1;
+
+    let s = &"key=value";
+    let _ = s.split_once('=').unwrap().1;
+
+    fn _f(s: &str) -> Option<&str> {
+        let _ = s.split_once('=')?.1;
+        let _ = s.split_once('=')?.1;
+        let _ = s.rsplit_once('=')?.0;
+        let _ = s.rsplit_once('=')?.0;
+        None
+    }
+
+    // Don't lint, slices don't have `split_once`
+    let _ = [0, 1, 2].splitn(2, |&x| x == 1).nth(1).unwrap();
+
+    // `rsplitn` gives the results in the reverse order of `rsplit_once`
+    let _ = "key=value".rsplit_once('=').unwrap().0;
+    let (_, _) = "key=value".rsplit_once('=').map(|(x, y)| (y, x)).unwrap();
+    let _ = s.rsplit_once('=').map(|x| x.0);
+}
+
+fn indirect() -> Option<()> {
+    let (l, r) = "a.b.c".split_once('.').unwrap();
+    
+    
+
+    let (l, r) = "a.b.c".split_once('.')?;
+    
+    
+
+    let (l, r) = "a.b.c".rsplit_once('.').unwrap();
+    
+    
+
+    let (l, r) = "a.b.c".rsplit_once('.')?;
+    
+    
+
+    // could lint, currently doesn't
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    let other = 1;
+    let l = iter.next()?;
+    let r = iter.next()?;
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    let mut mut_binding = iter.next()?;
+    let r = iter.next()?;
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    let tuple = (iter.next()?, iter.next()?);
+
+    // should not lint
+
+    let mut missing_unwrap = "a.b.c".splitn(2, '.');
+    let l = missing_unwrap.next();
+    let r = missing_unwrap.next();
+
+    let mut mixed_unrap = "a.b.c".splitn(2, '.');
+    let unwrap = mixed_unrap.next().unwrap();
+    let question_mark = mixed_unrap.next()?;
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    let same_name = iter.next()?;
+    let same_name = iter.next()?;
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    let shadows_existing = "d";
+    let shadows_existing = iter.next()?;
+    let r = iter.next()?;
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    let becomes_shadowed = iter.next()?;
+    let becomes_shadowed = "d";
+    let r = iter.next()?;
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    let l = iter.next()?;
+    let r = iter.next()?;
+    let third_usage = iter.next()?;
+
+    let mut n_three = "a.b.c".splitn(3, '.');
+    let l = n_three.next()?;
+    let r = n_three.next()?;
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    {
+        let in_block = iter.next()?;
+    }
+    let r = iter.next()?;
+
+    let mut lacks_binding = "a.b.c".splitn(2, '.');
+    let _ = lacks_binding.next()?;
+    let r = lacks_binding.next()?;
+
+    let mut mapped = "a.b.c".splitn(2, '.').map(|_| "~");
+    let l = iter.next()?;
+    let r = iter.next()?;
+
+    let mut assigned = "";
+    let mut iter = "a.b.c".splitn(2, '.');
+    let l = iter.next()?;
+    assigned = iter.next()?;
+
+    None
+}
+
+#[clippy::msrv = "1.51"]
+fn _msrv_1_51() {
+    // `str::split_once` was stabilized in 1.52. Do not lint this
+    let _ = "key=value".splitn(2, '=').nth(1).unwrap();
+
+    let mut iter = "a.b.c".splitn(2, '.');
+    let a = iter.next().unwrap();
+    let b = iter.next().unwrap();
+}
+
+#[clippy::msrv = "1.52"]
+fn _msrv_1_52() {
+    let _ = "key=value".split_once('=').unwrap().1;
+
+    let (a, b) = "a.b.c".split_once('.').unwrap();
+    
+    
+}

tests/ui/manual_split_once.rs

@@ -1,8 +1,6 @@
 #![warn(clippy::manual_split_once)]
 #![allow(unused, clippy::iter_skip_next, clippy::iter_nth_zero)]
 
-//@no-rustfix: need to change the suggestion to a multipart suggestion
-
 extern crate itertools;
 
 #[allow(unused_imports)]