Share the struct MAX_FIELDS constant

Extract the duplicated 10_000 struct field limit into a shared
StructType::MAX_FIELDS constant instead of mirroring it in rec_group.rs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: somdoron

crates/wasmtime/src/runtime/rec_group.rs

@@ -51,9 +51,6 @@ use wasmtime_environ::{
     WasmRefType, WasmStorageType, WasmStructType, WasmSubType, WasmValType,
 };
 
-/// Maximum number of fields in a struct, mirroring `StructType::from_wasm_struct_type`.
-const MAX_FIELDS: usize = 10_000;
-
 /// A process-global counter used to give each [`RecGroupBuilder`] a distinct id
 /// so that handles from one builder cannot be accidentally used with another.
 static NEXT_BUILDER_ID: AtomicUsize = AtomicUsize::new(0);
@@ -303,10 +300,11 @@ impl RecGroupBuilder {
         for (i, member) in members.iter().enumerate() {
             if let WasmCompositeInnerType::Struct(s) = &member.composite_type.inner {
                 ensure!(
-                    s.fields.len() <= MAX_FIELDS,
+                    s.fields.len() <= StructType::MAX_FIELDS,
                     "attempted to define struct type {i} with {} fields, but that is more than \
-                     the maximum supported number of fields ({MAX_FIELDS})",
+                     the maximum supported number of fields ({})",
                     s.fields.len(),
+                    StructType::MAX_FIELDS,
                 );
             }
         }

crates/wasmtime/src/runtime/types.rs

@@ -1853,6 +1853,9 @@ impl fmt::Display for StructType {
 }
 
 impl StructType {
+    /// Maximum number of fields supported in a struct type.
+    pub(crate) const MAX_FIELDS: usize = 10_000;
+
     /// Construct a new `StructType` with the given field types.
     ///
     /// This `StructType` will be final and without a supertype.
@@ -2058,13 +2061,13 @@ impl StructType {
         supertype: Option<EngineOrModuleTypeIndex>,
         ty: WasmStructType,
     ) -> Result<StructType> {
-        const MAX_FIELDS: usize = 10_000;
         let fields_len = ty.fields.len();
         ensure!(
-            fields_len <= MAX_FIELDS,
+            fields_len <= Self::MAX_FIELDS,
             "attempted to define a struct type with {fields_len} fields, but \
              that is more than the maximum supported number of fields \
-             ({MAX_FIELDS})",
+             ({})",
+            Self::MAX_FIELDS,
         );
 
         let ty = RegisteredType::new(