Ensure we don't subtract with underflow getting enum names (#5246)

* Ensure we don't subtract with underflow getting enum names

* Yep - forgot to run this

src/idl_gen_rust.cpp

@@ -698,14 +698,14 @@ class RustGenerator : public BaseGenerator {
       code_ += "pub fn enum_name_{{ENUM_NAME_SNAKE}}(e: {{ENUM_NAME}}) -> "
                "&'static str {";
 
-      code_ += "  let index: usize = e as usize\\";
+      code_ += "  let index = e as {{BASE_TYPE}}\\";
       if (enum_def.vals.vec.front()->value) {
         auto vals = GetEnumValUse(enum_def, *enum_def.vals.vec.front());
-        code_ += " - " + vals + " as usize\\";
+        code_ += " - " + vals + " as {{BASE_TYPE}}\\";
       }
       code_ += ";";
 
-      code_ += "  ENUM_NAMES_{{ENUM_NAME_CAPS}}[index]";
+      code_ += "  ENUM_NAMES_{{ENUM_NAME_CAPS}}[index as usize]";
       code_ += "}";
       code_ += "";
     }

tests/monster_test_generated.rs

@@ -227,8 +227,8 @@ const ENUM_NAMES_COLOR:[&'static str; 8] = [
 ];
 
 pub fn enum_name_color(e: Color) -> &'static str {
-  let index: usize = e as usize - Color::Red as usize;
-  ENUM_NAMES_COLOR[index]
+  let index = e as i8 - Color::Red as i8;
+  ENUM_NAMES_COLOR[index as usize]
 }
 
 #[allow(non_camel_case_types)]
@@ -293,8 +293,8 @@ const ENUM_NAMES_ANY:[&'static str; 4] = [
 ];
 
 pub fn enum_name_any(e: Any) -> &'static str {
-  let index: usize = e as usize;
-  ENUM_NAMES_ANY[index]
+  let index = e as u8;
+  ENUM_NAMES_ANY[index as usize]
 }
 
 pub struct AnyUnionTableOffset {}
@@ -360,8 +360,8 @@ const ENUM_NAMES_ANY_UNIQUE_ALIASES:[&'static str; 4] = [
 ];
 
 pub fn enum_name_any_unique_aliases(e: AnyUniqueAliases) -> &'static str {
-  let index: usize = e as usize;
-  ENUM_NAMES_ANY_UNIQUE_ALIASES[index]
+  let index = e as u8;
+  ENUM_NAMES_ANY_UNIQUE_ALIASES[index as usize]
 }
 
 pub struct AnyUniqueAliasesUnionTableOffset {}
@@ -427,8 +427,8 @@ const ENUM_NAMES_ANY_AMBIGUOUS_ALIASES:[&'static str; 4] = [
 ];
 
 pub fn enum_name_any_ambiguous_aliases(e: AnyAmbiguousAliases) -> &'static str {
-  let index: usize = e as usize;
-  ENUM_NAMES_ANY_AMBIGUOUS_ALIASES[index]
+  let index = e as u8;
+  ENUM_NAMES_ANY_AMBIGUOUS_ALIASES[index as usize]
 }
 
 pub struct AnyAmbiguousAliasesUnionTableOffset {}

tests/namespace_test/namespace_test1_generated.rs

@@ -84,8 +84,8 @@ const ENUM_NAMES_ENUM_IN_NESTED_NS:[&'static str; 3] = [
 ];
 
 pub fn enum_name_enum_in_nested_ns(e: EnumInNestedNS) -> &'static str {
-  let index: usize = e as usize;
-  ENUM_NAMES_ENUM_IN_NESTED_NS[index]
+  let index = e as i8;
+  ENUM_NAMES_ENUM_IN_NESTED_NS[index as usize]
 }
 
 // struct StructInNestedNS, aligned to 4