The default keyword should be honored on functions

[tsandall]

If you define a function with a default value, the default should be honored if all of the functions with the same name are undefined.

package test

default f(x) = 0

f(x) = x { x > 0 }

Today the default is ignored. Example:

$ opa eval -d x.rego 'data.test.f(1)'
{
  "result": [
    {
      "expressions": [
        {
          "value": 1,
          "text": "data.test.f(1)",
          "location": {
            "row": 1,
            "col": 1
          }
        }
      ]
    }
  ]
}

$ opa eval -d x.rego 'data.test.f(-1)'
{}

[srenatus]

Wasm does that already (see #3389).

[oren-zohar]

@tsandall any workaround for this?

[tsandall]

You can use else to define the default value:

package repl

f(x) = 1 {
        x > 1
}

else = 0 {
        true
}

> f(-1)
0

[oren-zohar]

@tsandall thanks for the quick response!
Small question, why do we need to add the:

else = 0 {
        true
}

inside the else clause? seems redundant no?

Wouldn't it be more elegant to have it like that:

package repl

f(x) = 1 {
        x > 1
} else = 0

I'm asking this since I noticed that opa fmt -w adds the same thing into the else clause if it's empty, even though it works the same.

[anderseknert]

Checking in from my vacation, and I'm happy that you went with the conservative approach here and made default functions similar to default rules @ashutosh-narkar 👍

Looking at the PR though, I don't see anything added to the documentation around this. Was that added elsewhere?

[ashutosh-narkar]

Hey @anderseknert good point. I'll update the docs to add a note about this.