Add duplicate name error reproducer

[gabotechs]

Which issue does this PR close?

• Related to Duplicate unqualified name error on unions #20123

Rationale for this change

Reproduces a duplicate name issue introduced in #19019.

Reverting the following code:

datafusion/datafusion/expr/src/expr_rewriter/mod.rs

Line 263 in 2e02cc1

_ => {

From:

 _ => {// maintain the original name when castinglet name = dst_schema.field(idx).name();Ok(expr.cast_to(new_type, src_schema)?.alias(name))}

to

 _ => expr.cast_to(new_type, src_schema),

Seems to fix the issue.

TODO: actually fix the issue before merging

What changes are included in this PR?

For now, just a reproducer test

Are these changes tested?

yes, by a new test

Are there any user-facing changes?

no

[alamb]

Nice find @gabotechs

[gabotechs]

cc @dd-annarose, merged the reproducer, in case you have time to look into this.

[dd-annarose]

@gabotechs ah just saw the issue was taken already. Did not get a notification for this ping

[nuno-faria]

That's quite the bug!

Projection: foo AS col1, bar AS col2
Union
Projection: foo, bar
Values: (Int64(100), Int64(200))
Projection: x, foo
Values: (Int32(300), Int64(400))

Because x has a different type, it will be casted to Int64. In the cast, an alias is added to the original name. However, in this case dst_schema will not contain the original column names, but rather the names of the first relation, since this is an union. So the second projection is temporarily foo (casted and alised) and foo, hence the duplicate error.

I will try to push a fix soon.

[gabotechs]

@gabotechs ah just saw the issue was taken already. Did not get a notification for this ping

@dd-annarose It seems like people have been really fast on tackling this. Maybe you can help with a review on #20146?

Thanks @nuno-faria for jumping into this!