Replace uses of unsafe with safe alternatives (#1714)

* Replace unsafe blocks with safe alternatives

* Replace unsafe blocks with safe alternatives

* update to fix tests

* use split_at(0) for consistensy

* Update src/lib.rs

---------

Co-authored-by: Nabil Wadih <nwadih@google.com>
Co-authored-by: Geoffroy Couprie <contact@geoffroycouprie.com>

src/traits.rs

@@ -419,8 +419,11 @@ impl<'a> Input for &'a str {
     P: Fn(Self::Item) -> bool,
   {
     match self.find(predicate) {
-      // find() returns a byte index that is already in the slice at a char boundary
-      Some(i) => unsafe { Ok((self.get_unchecked(i..), self.get_unchecked(..i))) },
+      // The position i is returned from str::find() which means it is within the bounds of the string
+      Some(i) => {
+        let (str1, str2) = self.split_at(i);
+        Ok((str2, str1))
+      }
       None => Err(Err::Incomplete(Needed::new(1))),
     }
   }
@@ -436,8 +439,11 @@ impl<'a> Input for &'a str {
   {
     match self.find(predicate) {
       Some(0) => Err(Err::Error(E::from_error_kind(self, e))),
-      // find() returns a byte index that is already in the slice at a char boundary
-      Some(i) => unsafe { Ok((self.get_unchecked(i..), self.get_unchecked(..i))) },
+      // The position i is returned from str::find() which means it is within the bounds of the string
+      Some(i) => {
+        let (str1, str2) = self.split_at(i);
+        Ok((str2, str1))
+      }
       None => Err(Err::Incomplete(Needed::new(1))),
     }
   }
@@ -451,15 +457,12 @@ impl<'a> Input for &'a str {
     P: Fn(Self::Item) -> bool,
   {
     match self.find(predicate) {
-      // find() returns a byte index that is already in the slice at a char boundary
-      Some(i) => unsafe { Ok((self.get_unchecked(i..), self.get_unchecked(..i))) },
-      // the end of slice is a char boundary
-      None => unsafe {
-        Ok((
-          self.get_unchecked(self.len()..),
-          self.get_unchecked(..self.len()),
-        ))
-      },
+      // The position i is returned from str::find() which means it is within the bounds of the string
+      Some(i) => {
+        let (str1, str2) = self.split_at(i);
+        Ok((str2, str1))
+      }
+      None => Ok(self.split_at(0)),
     }
   }
 
@@ -474,19 +477,18 @@ impl<'a> Input for &'a str {
   {
     match self.find(predicate) {
       Some(0) => Err(Err::Error(E::from_error_kind(self, e))),
-      // find() returns a byte index that is already in the slice at a char boundary
-      Some(i) => unsafe { Ok((self.get_unchecked(i..), self.get_unchecked(..i))) },
+      // The position i is returned from str::find() which means it is within the bounds of the string
+      Some(i) => {
+        let (str1, str2) = self.split_at(i);
+        Ok((str2, str1))
+      }
       None => {
         if self.is_empty() {
           Err(Err::Error(E::from_error_kind(self, e)))
         } else {
           // the end of slice is a char boundary
-          unsafe {
-            Ok((
-              self.get_unchecked(self.len()..),
-              self.get_unchecked(..self.len()),
-            ))
-          }
+          let (str1, str2) = self.split_at(self.len());
+          Ok((str2, str1))
         }
       }
     }