Breaking change in v0.20.0

Describe the bug

A breaking change was introduced here: https://github.com/axios/axios/pull/2844/files?file-filters[]=.js&hide-deleted-files=true#diff-597f69416721110963cbbdf72c6d4e6e30d77da5073041b4b10a702c0a7186f0R76

Previously a GET request would be able to include data, since before the change above util.merge would keep the data property passed in config. Now the mergeConfig function will ignore the data property in config, causing the request to be made without data.

Whether or not a GET request should be able to send a body is debatable I guess, but this change should probably be documented somewhere.

To Reproduce

var utils = require("./utils");
var mergeConfig = require("./core/mergeConfig");

console.log("--- mergeConfig --- ");
console.log(
  mergeConfig(
    { data: { hello: "world" } },
    {
      method: "get",
      url: "https://test.com",
    }
  )
);

console.log("--- utils.merge ---");
console.log(
  utils.merge(
    { data: { hello: "world" } },
    {
      method: "get",
      url: "https://test.com",
    }
  )
);

Result:

--- mergeConfig --- 
{ url: 'https://test.com', method: 'get' }
--- utils.merge ---
{ data: { hello: 'world' },
  method: 'get',
  url: 'https://test.com' }

Expected behavior

A clear and concise description of what you expected to happen.

Environment

• Axios Version [e.g. 0.18.0] 0.20.0
• Adapter [e.g. XHR/HTTP] HTTP
• Browser [e.g. Chrome, Safari] Node
• Browser Version [e.g. 22]
• Node.js Version [e.g. 13.0.1] v10.14.1
• OS: [e.g. iOS 12.1.0, OSX 10.13.4] OSX
• Additional Library Versions [e.g. React 16.7, React Native 0.58.0]

Additional context/Screenshots

Add any other context about the problem here. If applicable, add screenshots to help explain.

[nick-w-nick]

Just as a bump, this issue is impacting me as well. I just noticed it today after upgrading from 0.19.2 to 0.20.0.

I have several systems that interact with APIs that require a request body with certain GET requests, which are now not working after the upgrade since the data property in the config object is being ignored.

Behavior on 0.19.2

const config = {
    data: {
        prop1: 'prop1value',
        prop2: 'prop2value'
    }
}

Axios.get('https://website.com/api/endpoint', config);

Request being sent: GET https://website.com/api/endpoint Request Body:

{
    prop1: 'prop1value',
    prop2: 'prop2value'
}

Behavior on 0.20.0

const config = {
    data: {
        prop1: 'prop1value',
        prop2: 'prop2value'
    }
}

Axios.get('https://website.com/api/endpoint', config);

Request being sent: GET https://website.com/api/endpoint Request Body: (blank)

[ionTea]

I think so too, I’ll close this 👍