Add support for function paramets without names

Add support for flow functions with parameters that doesn't have a name.
Eg. `value: string => void`. It gives the argument a name equal to an
empty string: ''

Author: odinuge

README.md

@@ -224,6 +224,7 @@ type Props = {
   literalsAndUnion: 'string' | 'otherstring' | number,
   arr: Array<any>,
   func?: (value: string) => void,
+  noParameterName?: string => void,
   obj?: { subvalue: ?boolean },
 };
 
@@ -288,6 +289,20 @@ we are getting this output:
       },
       "required":false
     },
+    "noParameterName":{
+      "flowType":{
+        "name":"signature",
+        "type":"function",
+        "raw":"string => void",
+        "signature":{
+          "arguments":[
+            { "name":"", "type":{ "name":"string" } }
+          ],
+          "return":{ "name":"void" }
+        }
+      },
+      "required":false
+    },
     "obj":{
       "flowType":{
         "name":"signature",

src/utils/__tests__/getFlowType-test.js

@@ -139,6 +139,27 @@ describe('getFlowType', () => {
     }, raw: '(p1: number, p2: ?string) => boolean'});
   });
 
+
+  it('detects function signature types without parameter names', () => {
+    var typePath = expression('x: (number, ?string) => boolean').get('typeAnnotation').get('typeAnnotation');
+    expect(getFlowType(typePath)).toEqual({name: 'signature', type: 'function', signature: {
+      arguments: [
+        { name: '', type: { name: 'number' }},
+        { name: '', type: { name: 'string', nullable: true }},
+      ],
+      return: { name: 'boolean' },
+    }, raw: '(number, ?string) => boolean'});
+  });
+
+  it('detects function signature type with single parmeter without name', () => {
+    var typePath = expression('x: string => boolean').get('typeAnnotation').get('typeAnnotation');
+    expect(getFlowType(typePath)).toEqual({name: 'signature', type: 'function', signature: {
+      arguments: [
+        { name: '', type: { name: 'string' }},
+      ],
+      return: { name: 'boolean' },
+    }, raw: 'string => boolean'});
+  });
   it('detects callable signature type', () => {
     var typePath = expression('x: { (str: string): string, token: string }').get('typeAnnotation').get('typeAnnotation');
     expect(getFlowType(typePath)).toEqual({name: 'signature', type: 'object', signature: {

src/utils/getNameOrValue.js

@@ -25,6 +25,8 @@ export default function getNameOrValue(path: NodePath, raw?: boolean): string {
       return node.name;
     case types.Literal.name:
       return raw ? node.raw : node.value;
+    case types.FunctionTypeParam.name:
+      return '';
     default:
       throw new TypeError('Argument must be an Identifier or a Literal');
   }