Return None for optional primite field if its version is less than actingVersion.

build.gradle

@@ -677,6 +677,7 @@ tasks.register('generateRustTestCodecs', JavaExec) {
             'sbe-tool/src/test/resources/issue987.xml',
             'sbe-tool/src/test/resources/issue1028.xml',
             'sbe-tool/src/test/resources/issue1057.xml',
+            'sbe-tool/src/test/resources/issue1066.xml',
             'sbe-tool/src/test/resources/fixed-sized-primitive-array-types.xml',
             'sbe-tool/src/test/resources/example-bigendian-test-schema.xml',
             'sbe-tool/src/test/resources/nested-composite-name.xml',

rust/Cargo.toml

@@ -18,6 +18,7 @@ issue_984 = { path = "../generated/rust/issue984" }
 issue_987 = { path = "../generated/rust/issue987" }
 issue_1028 = { path = "../generated/rust/issue1028" }
 issue_1057 = { path = "../generated/rust/issue1057" }
+issue_1066 = { path = "../generated/rust/issue1066" }
 baseline_bigendian = { path = "../generated/rust/baseline-bigendian" }
 nested_composite_name = { path = "../generated/rust/nested-composite-name" }
 fixed_sized_primitive_array = { path = "../generated/rust/fixed_sized_primitive_array" }

rust/tests/issue_1066_test.rs

@@ -0,0 +1,40 @@
+use issue_1066::{
+    issue_1066_codec,
+    issue_1066_codec::{Issue1066Decoder, Issue1066Encoder},
+    *,
+};
+
+#[test]
+fn decode_optional_primitive_field() {
+    let mut buffer = vec![0u8; 256];
+
+    // Create a message with `field` set.
+    let mut encoder = Issue1066Encoder::default().wrap(
+        WriteBuf::new(&mut buffer),
+        message_header_codec::ENCODED_LENGTH,
+    );
+    encoder.field(10);
+
+    // Drop encoder to drop the mut reference for the buffer.
+    drop(encoder);
+
+    // Create a decoder for the message, but stating that the version is 1, instead of 2
+    // which is the acting version for `field`. Thus, `field()` must return `None`.
+    let decoder = Issue1066Decoder::default().wrap(
+        ReadBuf::new(&mut buffer),
+        message_header_codec::ENCODED_LENGTH,
+        issue_1066_codec::SBE_BLOCK_LENGTH,
+        1,
+    );
+    assert!(decoder.field().is_none());
+
+    // Create a decoder for the message, but stating that the version is 1, instead of 2
+    // which is the acting version for `field`. Thus, `field()` must return `None`.
+    let decoder = Issue1066Decoder::default().wrap(
+        ReadBuf::new(&mut buffer),
+        message_header_codec::ENCODED_LENGTH,
+        issue_1066_codec::SBE_BLOCK_LENGTH,
+        2,
+    );
+    assert_eq!(decoder.field(), Some(10));
+}

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/rust/RustGenerator.java

@@ -894,6 +894,13 @@ private static void generatePrimitiveOptionalDecoder(
             formatFunctionName(name),
             rustPrimitiveType);
 
+        if (fieldToken.version() > 0)
+        {
+            indent(sb, level + 1, "if self.acting_version() < %d {\n", fieldToken.version());
+            indent(sb, level + 2, "return None;\n");
+            indent(sb, level + 1, "}\n\n");
+        }
+
         indent(sb, level + 1, "let value = self.get_buf().get_%s_at(self.%s);\n",
             rustPrimitiveType,
             getBufOffset(fieldToken));

sbe-tool/src/test/resources/issue1066.xml

@@ -0,0 +1,18 @@
+<messageSchema xmlns:sbe="http://fixprotocol.io/2016/sbe" package="issue1066" id="1066" version="2"
+	semanticVersion="1.0.0" byteOrder="littleEndian">
+	<types>
+		<composite name="messageHeader">
+			<type name="blockLength" primitiveType="uint16"
+				description="Length of the root of the FIX message contained before repeating groups or variable/conditions fields." />
+			<type name="templateId" primitiveType="uint16"
+				description="Template ID used to encode the message." />
+			<type name="schemaId" primitiveType="uint16"
+				description="ID of the system publishing the message." />
+			<type name="version" primitiveType="uint16" description="Schema version." />
+		</composite>
+	</types>
+	<message name="issue1066" id="1">
+		<field name="field" id="1" type="uint16" semanticType="Int" sinceVersion="2"
+			presence="optional" />
+	</message>
+</messageSchema>