Make size_hint private

serde_core/src/private/content.rs

@@ -1,7 +1,6 @@
-use crate::de::{
-    self, size_hint, Deserialize, Deserializer, EnumAccess, MapAccess, SeqAccess, Visitor,
-};
+use crate::de::{self, Deserialize, Deserializer, EnumAccess, MapAccess, SeqAccess, Visitor};
 use crate::lib::*;
+use crate::private::size_hint;
 
 // Used from generated code to buffer the contents of the Deserializer when
 // deserializing untagged enums and internally tagged enums.

serde_core/src/private/mod.rs

@@ -1,6 +1,9 @@
 #[cfg(all(not(no_serde_derive), any(feature = "std", feature = "alloc")))]
 mod content;
 
+#[doc(hidden)]
+pub mod size_hint;
+
 #[doc(hidden)]
 pub mod string;
 

serde_core/src/private/size_hint.rs

@@ -0,0 +1,30 @@
+#[cfg(any(feature = "std", feature = "alloc"))]
+use crate::lib::*;
+
+pub fn from_bounds<I>(iter: &I) -> Option<usize>
+where
+    I: Iterator,
+{
+    helper(iter.size_hint())
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub fn cautious<Element>(hint: Option<usize>) -> usize {
+    const MAX_PREALLOC_BYTES: usize = 1024 * 1024;
+
+    if mem::size_of::<Element>() == 0 {
+        0
+    } else {
+        cmp::min(
+            hint.unwrap_or(0),
+            MAX_PREALLOC_BYTES / mem::size_of::<Element>(),
+        )
+    }
+}
+
+fn helper(bounds: (usize, Option<usize>)) -> Option<usize> {
+    match bounds {
+        (lower, Some(upper)) if lower == upper => Some(upper),
+        _ => None,
+    }
+}