Add overflow checking for str::get with inclusive ranges

Fixes #42401

Author: scottmcm

src/libcollections/tests/lib.rs

@@ -22,6 +22,7 @@
 #![feature(rand)]
 #![feature(slice_rotate)]
 #![feature(splice)]
+#![feature(str_checked_slicing)]
 #![feature(str_escape)]
 #![feature(test)]
 #![feature(unboxed_closures)]

src/libcollections/tests/str.rs

@@ -358,6 +358,48 @@ fn test_slice_fail() {
     &"中华Việt Nam"[0..2];
 }
 
+#[test]
+#[should_panic]
+fn test_str_slice_rangetoinclusive_max_panics() {
+    &"hello"[...usize::max_value()];
+}
+
+#[test]
+#[should_panic]
+fn test_str_slice_rangeinclusive_max_panics() {
+    &"hello"[1...usize::max_value()];
+}
+
+#[test]
+#[should_panic]
+fn test_str_slicemut_rangetoinclusive_max_panics() {
+    let mut s = "hello".to_owned();
+    let s: &mut str = &mut s;
+    &mut s[...usize::max_value()];
+}
+
+#[test]
+#[should_panic]
+fn test_str_slicemut_rangeinclusive_max_panics() {
+    let mut s = "hello".to_owned();
+    let s: &mut str = &mut s;
+    &mut s[1...usize::max_value()];
+}
+
+#[test]
+fn test_str_get_maxinclusive() {
+    let mut s = "hello".to_owned();
+    {
+        let s: &str = &s;
+        assert_eq!(s.get(...usize::max_value()), None);
+        assert_eq!(s.get(1...usize::max_value()), None);
+    }
+    {
+        let s: &mut str = &mut s;
+        assert_eq!(s.get(...usize::max_value()), None);
+        assert_eq!(s.get(1...usize::max_value()), None);
+    }
+}
 
 #[test]
 fn test_is_char_boundary() {

src/libcore/str/mod.rs

@@ -1918,11 +1918,19 @@ mod traits {
         type Output = str;
         #[inline]
         fn get(self, slice: &str) -> Option<&Self::Output> {
-            (self.start..self.end+1).get(slice)
+            if let Some(end) = self.end.checked_add(1) {
+                (self.start..end).get(slice)
+            } else {
+                None
+            }
         }
         #[inline]
         fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
-            (self.start..self.end+1).get_mut(slice)
+            if let Some(end) = self.end.checked_add(1) {
+                (self.start..end).get_mut(slice)
+            } else {
+                None
+            }
         }
         #[inline]
         unsafe fn get_unchecked(self, slice: &str) -> &Self::Output {
@@ -1953,15 +1961,15 @@ mod traits {
         type Output = str;
         #[inline]
         fn get(self, slice: &str) -> Option<&Self::Output> {
-            if slice.is_char_boundary(self.end + 1) {
+            if self.end < usize::max_value() && slice.is_char_boundary(self.end + 1) {
                 Some(unsafe { self.get_unchecked(slice) })
             } else {
                 None
             }
         }
         #[inline]
         fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
-            if slice.is_char_boundary(self.end + 1) {
+            if self.end < usize::max_value() && slice.is_char_boundary(self.end + 1) {
                 Some(unsafe { self.get_unchecked_mut(slice) })
             } else {
                 None