Select with prop multiple=true is buggy when value is Arr<Obj>

If we pass value as Array of Objects to Select component when multiple=true, it tends to create duplicate entry for same MenuItem in the drop-down.

• This is not a v0.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior 🤔

Suppose if we pass initialise state as -

state= {
    value: [{name: 'Item1'}]
}

And suppose I click on the same item on the drop-down, the item should be unselected and the onChange method should receive an empty array instead.

Current Behavior 😯

I click on the same item on the drop-down, and the onChange method should receive an array of length 2, with the same object repeated twice.

Steps to Reproduce 🕹

I think I found the cause of the bug. Link to the function causing bug https://github.com/mui-org/material-ui/blob/master/packages/material-ui/src/Select/SelectInput.js#L125

The handleItemClick function implementation is as follows -

const handleItemClick = child => event => {
    if (!multiple) {
      update(false, event);
    }

    if (onChange) {
      let newValue;

      if (multiple) {
        newValue = Array.isArray(value) ? [...value] : [];
/*
Here, suppose newValue is [{name: 'Item1'}] and child.props.value is {name: 'Item1'}.
The itemIndex is computed as -1 and it results to insertion of duplicate element, rather than splicing it.
*/

        const itemIndex = value.indexOf(child.props.value);


        if (itemIndex === -1) {
          newValue.push(child.props.value);
        } else {
          newValue.splice(itemIndex, 1);
        }
      } else {
        newValue = child.props.value;
      }

      event.persist();
      event.target = { value: newValue, name };
      onChange(event, child);
    }
  };

Link:

1. Sandbox link - https://codesandbox.io/s/create-react-app-5grs7
2. Probable Issue in codebase - https://github.com/mui-org/material-ui/blob/master/packages/material-ui/src/Select/SelectInput.js#L125

Context 🔦

I was trying to use it for my Project

Your Environment 🌎

Tech	Version
Material-UI	v3.9.2
React	16.5.2
Browser	Chrome Version 75.0.3770.142 (Official Build) (64-bit)

[joshwooding]

This is related to https://github.com/mui-org/material-ui/issues/10845 and a lot of other issues. I’m tempted to close this as a duplicate. You can kind of fix this by using the reference of the object as the default value e.g. https://codesandbox.io/s/create-react-app-vgyz6

[joshwooding]

@akshatnitd I was just speaking about the code.