Feature request: [no-shadow] It would really help, if the error message would show where the original identifier has been defined

[doberkofler]

What rule do you want to change?
no-shadow

Does this change cause the rule to produce more or fewer warnings?
The same

How will the change be implemented? (New option, new default behavior, etc.)?
Just a change in the error message

Please provide some example code that this change will affect:

In my experience, the no-shadow rule could greatly benefit from an error message that also describes where the identifier has already been defined and not only where the redefinition has occurred.

var a = 3;
function b() {
    var a = 10;
}

What does the rule currently do for this code?

The error 3:9 - 'a' is already declared in the upper scope. (no-shadow) explains that a has already be declared somewhere but not exactly where the original declaration has been made.

What will the rule do after it's changed?

An improved error like 3:9 - 'a' is already declared in the upper scope 1:5. (no-shadow) would additionally inform that the original definition is in line 1 column 5 and greatly improved the experience.

Are you willing to submit a pull request to implement this change?
Not sure if I have the required skills.

Versions

package	version
ESLint	7.8.0
node	14.8.0

[anikethsaha]

Thanks for the issue

Make sense to me.

[mdjermanovic]

Makes sense to me, too. I'll champion this.

[t-mangoe]

I have worked on this issue.
I will open pull request, if you like, please check and review my codes.

[btmills]

This is a nice improvement 👍 marking as accepted since this has support from three team members including a champion.