[golang] Add meta attribute PRESENCE to generated codecs. Issue real-…

…logic#483.

build.gradle

@@ -523,6 +523,7 @@ task(generateGolangCodecsWithXSD, type: JavaExec) {
             'sbe-tool/src/test/resources/FixBinary.xml',
             'sbe-tool/src/test/resources/issue435.xml',
             'sbe-tool/src/test/resources/issue472.xml',
+            'sbe-tool/src/test/resources/issue483.xml',
             'sbe-tool/src/test/resources/since-deprecated-test-schema.xml',
             'sbe-tool/src/test/resources/example-bigendian-test-schema.xml',
             'gocode/resources/example-composite.xml',

gocode/src/issue483/Issue483_test.go

@@ -0,0 +1,29 @@
+package issue483
+
+import (
+	"testing"
+)
+
+func TestPresence(t *testing.T) {
+	issue483 := new(Issue483)
+
+    if issue483.UnsetMetaAttribute(4) != "required" {
+        t.Log("Unset attribute's presence should be 'required'")
+        t.Fail()
+    }
+
+    if issue483.RequiredMetaAttribute(4) != "required" {
+        t.Log("Required attribute's presence should be 'required'")
+        t.Fail()
+    }
+
+    if issue483.ConstantMetaAttribute(4) != "constant" {
+        t.Log("Constant attribute's presence should be 'constant'")
+        t.Fail()
+    }
+
+    if issue483.OptionalMetaAttribute(4) != "optional" {
+        t.Log("Optional attribute's presence should be 'optional'")
+        t.Fail()
+    }
+}

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/golang/GolangGenerator.java

@@ -2142,6 +2142,8 @@ private static void generateFieldMetaAttributeMethod(
         final String epoch = encoding.epoch() == null ? "" : encoding.epoch();
         final String timeUnit = encoding.timeUnit() == null ? "" : encoding.timeUnit();
         final String semanticType = encoding.semanticType() == null ? "" : encoding.semanticType();
+        final String presence = encoding.presence() == null ? "" : encoding.presence().toString().toLowerCase();
+
         sb.append(String.format(
             "\nfunc (%1$s %2$s) %3$sMetaAttribute(meta int) string {\n" +
             "\tswitch meta {\n" +
@@ -2151,6 +2153,8 @@ private static void generateFieldMetaAttributeMethod(
             "\t\treturn \"%5$s\"\n" +
             "\tcase 3:\n" +
             "\t\treturn \"%6$s\"\n" +
+            "\tcase 4:\n" +
+            "\t\treturn \"%7$s\"\n" +
             "\t}\n" +
             "\treturn \"\"\n" +
             "}\n",
@@ -2159,7 +2163,8 @@ private static void generateFieldMetaAttributeMethod(
             toUpperFirstChar(token.name()),
             epoch,
             timeUnit,
-            semanticType));
+            semanticType,
+            presence));
     }
 
     private CharSequence generateMinValueLiteral(final PrimitiveType primitiveType, final Encoding encoding)