Empty string in Enum got converted to '0'

[fhewitt]

When using empty string '' in string Enum used a input parameter, it got converted as '0'.

So imagine an enum like:

export enum MyThings {
    Undefined = '',
    Something = 'Something',
    Otherwise = 'Another Something',

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Expected Behavior

I would expect that the empty string is returned in the swagger doc.

    "MyThings ": {
        "enum": [
            "",
            "Something",
            "Another Something"
        ],
        "type": "string"
    },

And the '' value should be accepted during data validation.

Current Behavior

But I got that in swagger config and for validation:

    "MyThings ": {
        "enum": [
            "0",
            "Something",
            "Another Something"
        ],
        "type": "string"
    },

Well it's 0 because it's in first position, but moving it elsewhere, it will take the index of the position:

    "MyThings ": {
        "enum": [
            "Something",
            "Another Something",
            "2"
        ],
        "type": "string"
    },

Trying to pass empty string as the value to end point, I got the error "Should be one of [0, Something, Another Something]"

Workaround

You can change the empty string for something else, like a single space, dash or the word 'Undefined'. But this break Boolean conversion and seems counter-intuitive.

Context (Environment)

Version of the library: 2.3.8 & 2.4.11
Version of NodeJS: 10.14.1

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Detailed Description

Breaking change?

This change the current behaviour, so it's a breaking change in principle. But this seems unlikely that anyone have used empty string in enum as it is.

[fhewitt]

I'm not familiar enough with this code to propose a PR, but I suspect that the issue is around the typeResolver.ts line 286, where we do return getEnumValue(member) || String(index); Because '' is falsy, this defaults to the index. I would suggest to change for:

        const enumValue = getEnumValue(member);
        return !!enumValue || enumValue === '' ? enumValue : String(index);

It still pass the testing, seem to work with what I read of string enum in TypeScript doc. Unsure if this require additionnal testing (which would probably goes in unit/swagger/definitionsGeneration/definitions.spec.ts, but after that I'm a bit lost on the proper approach).

In fact, if this seems reasonable to maintainers, and with minimal direction for unit test if deemed necessary, I can propose a PR.

[dgreene1]

Before someone can take this on, can you confirm that an empty string is even a valid enum value in OpenAPI?

Because this seems strange:

MyEnum:
  type: string
    - 
    - Something
    - Another Something

Since this is a rare use case, I suspect that it won’t get picked up unless you or someone who needs the use case is willing to put in a PR. I apologize for being that direct, but I want to clarify that this is lower priority than some of the larger initiatives that are coming up. And since it seems important to you, I wanted to encourage you to take up the PR.

Note: the workaround is to use an abstraction enum that does not have an empty string value and but is instead a nullable enum.

[fhewitt]

My issue is that I have not full control over the data, I don't receive null, but empty string from the third party. But I can temper the value before I sent it back to our API.

Seem valid in OpenAPI, even if it could looks a bit weird in documentation.

I push the test further, but even by changing the model to add the empty string in allowed values, it still raise the error at runtime, I suspect that the validation run a "non falsy" check on the value. If I got some more time soon, I will continue the investigation and propose a PR.

[rgripper]

Validation also doesn't work properly with empty string enum value.
Could we have this check in validateEnum method:

tsoa/src/routeGeneration/templateHelpers.ts

Lines 237 to 240 in 28e599d

	const enumValue = members.find(member => {
	return member === String(value);
	});
	if (!enumValue) {

changed to:
if (enumValue === undefined) {

[dgreene1]

Sure as long as that doesn’t break the other unit tests. Please make a PR.

[dgreene1]

Released in 2.5.3