From 23fd95a5e99acf35b471ca9b01230d7578bfac5f Mon Sep 17 00:00:00 2001
From: max <36980911+pr2502@users.noreply.github.com>
Date: Sat, 8 Jan 2022 23:10:20 +0100
Subject: [PATCH] fix underflow in `check_manual_split_once` lint

---
 clippy_lints/src/methods/str_splitn.rs |  6 +++---
 tests/ui/crashes/ice-8250.rs           |  6 ++++++
 tests/ui/crashes/ice-8250.stderr       | 18 ++++++++++++++++++
 3 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 tests/ui/crashes/ice-8250.rs
 create mode 100644 tests/ui/crashes/ice-8250.stderr

diff --git a/clippy_lints/src/methods/str_splitn.rs b/clippy_lints/src/methods/str_splitn.rs
index 70f20da1d6d..e8a3562c393 100644
--- a/clippy_lints/src/methods/str_splitn.rs
+++ b/clippy_lints/src/methods/str_splitn.rs
@@ -45,16 +45,16 @@ pub(super) fn check_manual_split_once(
         IterUsageKind::Next | IterUsageKind::Second => {
             let self_deref = {
                 let adjust = cx.typeck_results().expr_adjustments(self_arg);
-                if adjust.is_empty() {
+                if adjust.len() < 2 {
                     String::new()
                 } else if cx.typeck_results().expr_ty(self_arg).is_box()
                     || adjust
                         .iter()
                         .any(|a| matches!(a.kind, Adjust::Deref(Some(_))) || a.target.is_box())
                 {
-                    format!("&{}", "*".repeat(adjust.len() - 1))
+                    format!("&{}", "*".repeat(adjust.len().saturating_sub(1)))
                 } else {
-                    "*".repeat(adjust.len() - 2)
+                    "*".repeat(adjust.len().saturating_sub(2))
                 }
             };
             if matches!(usage.kind, IterUsageKind::Next) {
diff --git a/tests/ui/crashes/ice-8250.rs b/tests/ui/crashes/ice-8250.rs
new file mode 100644
index 00000000000..d9a5ee1162a
--- /dev/null
+++ b/tests/ui/crashes/ice-8250.rs
@@ -0,0 +1,6 @@
+fn _f(s: &str) -> Option<()> {
+    let _ = s[1..].splitn(2, '.').next()?;
+    Some(())
+}
+
+fn main() {}
diff --git a/tests/ui/crashes/ice-8250.stderr b/tests/ui/crashes/ice-8250.stderr
new file mode 100644
index 00000000000..04ea4456656
--- /dev/null
+++ b/tests/ui/crashes/ice-8250.stderr
@@ -0,0 +1,18 @@
+error: manual implementation of `split_once`
+  --> $DIR/ice-8250.rs:2:13
+   |
+LL |     let _ = s[1..].splitn(2, '.').next()?;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `s[1..].split_once('.').map_or(s[1..], |x| x.0)`
+   |
+   = note: `-D clippy::manual-split-once` implied by `-D warnings`
+
+error: unnecessary use of `splitn`
+  --> $DIR/ice-8250.rs:2:13
+   |
+LL |     let _ = s[1..].splitn(2, '.').next()?;
+   |             ^^^^^^^^^^^^^^^^^^^^^ help: try this: `s[1..].split('.')`
+   |
+   = note: `-D clippy::needless-splitn` implied by `-D warnings`
+
+error: aborting due to 2 previous errors
+