Don't treat optional, constant, body params as required (#981)

This makes the behavior consistent with how optional, constant header
and query parameters are handled.

packages/autorest.go/src/generator/fake/servers.ts

@@ -361,14 +361,14 @@ function dispatchForOperationBody(clientPkg: string, receiverName: string, op: O
     // nothing to do for binary media type
   } else if (mediaType === 'Text') {
     const bodyParam = values(aggregateParameters(op)).where((each: Parameter) => { return each.protocol.http?.in === 'body'; }).first();
-    if (bodyParam && bodyParam.schema.type !== SchemaType.Constant) {
+    if (bodyParam && !(bodyParam.required === true && bodyParam.schema.type === SchemaType.Constant)) {
       imports.add('github.com/Azure/azure-sdk-for-go/sdk/azcore/fake', 'azfake');
       content += '\tbody, err := server.UnmarshalRequestAsText(req)\n';
       content += '\tif err != nil {\n\t\treturn nil, err\n\t}\n';
     }
   } else if (mediaType === 'JSON' || mediaType === 'XML') {
     const bodyParam = values(aggregateParameters(op)).where((each: Parameter) => { return each.protocol.http?.in === 'body'; }).first();
-    if (bodyParam && bodyParam.schema.type !== SchemaType.Constant) {
+    if (bodyParam && !(bodyParam.required === true && bodyParam.schema.type === SchemaType.Constant)) {
       imports.add('github.com/Azure/azure-sdk-for-go/sdk/azcore/fake', 'azfake');
       if (bodyParam.schema.type === SchemaType.ByteArray) {
         let format = 'Std';

packages/autorest.go/src/generator/operations.ts

@@ -757,7 +757,7 @@ function createProtocolRequest(group: OperationGroup, op: Operation, imports: Im
       imports.add('github.com/Azure/azure-sdk-for-go/sdk/azcore/streaming');
       setBody = `req.SetBody(streaming.NopCloser(bytes.NewReader(${body})), "application/${mediaType.toLowerCase()}")`;
     }
-    if (bodyParam!.required || bodyParam!.schema.type === SchemaType.Constant) {
+    if (bodyParam!.required) {
       text += `\t${emitSetBodyWithErrCheck(setBody)}`;
       text += '\treturn req, nil\n';
     } else {

packages/autorest.go/src/transform/transform.ts

@@ -572,8 +572,8 @@ async function processOperationRequests(session: Session<CodeModel>) {
           } else if (dupe.schema !== param.schema) {
             throw new Error(`parameter group ${paramGroupName} contains overlapping parameters with different schemas`);
           }
-        } else if (param.implementation === ImplementationLocation.Method && param.required !== true && !(param.schema.type === SchemaType.Constant && param.protocol.http!.in === 'body')) {
-          // include non-required constants that aren't body params in the optional values struct.
+        } else if (param.implementation === ImplementationLocation.Method && param.required !== true) {
+          // include all non-required method params in the optional values struct.
           (<GroupProperty>op.language.go!.optionalParamGroup).originalParameter.push(param);
           // associate the group with the param
           param.language.go!.paramGroup = op.language.go!.optionalParamGroup;