fix(core): Incorrect arg type on Fn.eachMemberIn (#2958)

Changed the type of the second argument to `Fn.eachMemberIn` to an array
of `string`s, such that it can be used at all.

BREAKING CHANGE: All instance methods of `Fn` were made `static`, and
                 the `Fn` constructor was made private.

Fixes #2950

Author: RomainMuller

Diff for: packages/@aws-cdk/cdk/lib/fn.ts

@@ -240,7 +240,7 @@ export class Fn {
    * of strings.
    * @returns an FnCondition token
    */
-  public conditionEachMemberEquals(listOfStrings: string[], value: string): ICfnConditionExpression {
+  public static conditionEachMemberEquals(listOfStrings: string[], value: string): ICfnConditionExpression {
     return new FnEachMemberEquals(listOfStrings, value);
   }
 
@@ -255,7 +255,7 @@ export class Fn {
    * strings_to_check parameter.
    * @returns an FnCondition token
    */
-  public conditionEachMemberIn(stringsToCheck: string[], stringsToMatch: string): ICfnConditionExpression {
+  public static conditionEachMemberIn(stringsToCheck: string[], stringsToMatch: string[]): ICfnConditionExpression {
     return new FnEachMemberIn(stringsToCheck, stringsToMatch);
   }
 
@@ -266,7 +266,7 @@ export class Fn {
    * Parameters in the AWS CloudFormation User Guide.
    * @returns a token represented as a string array
    */
-  public refAll(parameterType: string): string[] {
+  public static refAll(parameterType: string): string[] {
     return Token.asList(new FnRefAll(parameterType));
   }
 
@@ -280,7 +280,7 @@ export class Fn {
    * value.
    * @returns a token represented as a string
    */
-  public valueOf(parameterOrLogicalId: string, attribute: string): string {
+  public static valueOf(parameterOrLogicalId: string, attribute: string): string {
     return new FnValueOf(parameterOrLogicalId, attribute).toString();
   }
 
@@ -294,9 +294,11 @@ export class Fn {
    * value. For more information about attributes, see Supported Attributes.
    * @returns a token represented as a string array
    */
-  public valueOfAll(parameterType: string, attribute: string): string[] {
+  public static valueOfAll(parameterType: string, attribute: string): string[] {
     return Token.asList(new FnValueOfAll(parameterType, attribute));
   }
+
+  private constructor() { }
 }
 
 /**
@@ -577,8 +579,8 @@ class FnEachMemberIn extends FnConditionBase {
    * @param stringsToCheck A list of strings, such as "A", "B", "C". AWS CloudFormation checks whether each member in the strings_to_check parameter is in the strings_to_match parameter.
    * @param stringsToMatch A list of strings, such as "A", "B", "C". Each member in the strings_to_match parameter is compared against the members of the strings_to_check parameter.
    */
-  constructor(stringsToCheck: any, stringsToMatch: any) {
-    super('Fn::EachMemberIn', [ [stringsToCheck], stringsToMatch ]);
+  constructor(stringsToCheck: string[], stringsToMatch: string[]) {
+    super('Fn::EachMemberIn', [stringsToCheck, stringsToMatch]);
   }
 }
 
@@ -685,4 +687,4 @@ class FnJoin implements IResolvable {
     const resolvedValues = this.listOfValues.map(context.resolve);
     return this._resolvedValues = minimalCloudFormationJoin(this.delimiter, resolvedValues);
   }
-}
+}

Diff for: packages/@aws-cdk/cdk/test/test.fn.ts

@@ -126,6 +126,19 @@ export = nodeunit.testCase({
         { verbose: true }
       );
     }),
+    'Fn::EachMemberIn': asyncTest(async (test) => {
+      const stack = new Stack();
+      const eachMemberIn = Fn.conditionEachMemberIn(
+        Fn.valueOfAll('AWS::EC2::Subnet::Id', 'VpcId'),
+        Fn.refAll('AWS::EC2::VPC::Id')
+      );
+      test.deepEqual(stack.resolve(eachMemberIn), {
+        'Fn::EachMemberIn': [
+          { 'Fn::ValueOfAll': ['AWS::EC2::Subnet::Id', 'VpcId'] },
+          { 'Fn::RefAll': 'AWS::EC2::VPC::Id'}
+        ]
+      });
+    }),
   },
 });