chore: yoink from #2437

libs/deer/json/src/lib.rs

@@ -7,6 +7,7 @@ mod deserializer;
 mod error;
 mod number;
 mod object;
+mod skip;
 mod token;
 
 extern crate alloc;

libs/deer/json/src/skip.rs

@@ -0,0 +1,45 @@
+use crate::{deserializer::Deserializer, Token};
+
+fn scan_object(deserializer: &Deserializer, stop: &Token) -> usize {
+    let mut objects: usize = 0;
+    let mut arrays: usize = 0;
+
+    let mut n = 0;
+
+    loop {
+        let Some(token) = deserializer.peek_n(n) else {
+            // we're at the end
+            return n;
+        };
+
+        if token == *stop && arrays == 0 && objects == 0 {
+            // we're at the outer layer, meaning we can know where we end
+            // need to increment by one as we want to also skip the ObjectEnd
+            return n + 1;
+        }
+
+        match token {
+            Token::Array { .. } => arrays += 1,
+            Token::ArrayEnd => arrays = arrays.saturating_sub(1),
+            Token::Object { .. } => objects += 1,
+            Token::ObjectEnd => objects = objects.saturating_sub(1),
+            _ => {}
+        }
+
+        n += 1;
+    }
+}
+
+/// Skips all tokens required for the start token, be aware that the start token should no longer be
+/// on the tape
+pub(crate) fn skip_tokens(deserializer: &mut Deserializer, start: &Token) {
+    let n = match start {
+        Token::Array { .. } => scan_object(&*deserializer, &Token::ArrayEnd),
+        Token::Object { .. } => scan_object(&*deserializer, &Token::ObjectEnd),
+        _ => 0,
+    };
+
+    if n > 0 {
+        deserializer.tape_mut().bump_n(n);
+    }
+}