wasm: only returns first binding

[srenatus]

$ opa eval -t wasm 'xs := ["foo", "bar"]; xs[x]' --format=pretty
+---+---------------+-------+
| x |      xs       | xs[x] |
+---+---------------+-------+
| 1 | ["foo","bar"] | "bar" |
+---+---------------+-------+

$ opa eval -t rego 'xs := ["foo", "bar"]; xs[x]' --format=pretty
+---+---------------+-------+
| x |      xs       | xs[x] |
+---+---------------+-------+
| 0 | ["foo","bar"] | "foo" |
| 1 | ["foo","bar"] | "bar" |
+---+---------------+-------+

[tsandall]

Aha, here's the offending line:

https://github.com/open-policy-agent/opa/blob/master/rego/rego.go#L1927

[tsandall]

@srenatus for tomorrow...

Looks like there's another case that's not handled:

torin:~$ opa eval -t wasm 'x := [1,1]; x[_]'
{
  "result": [
    {
      "expressions": [
        {
          "value": true,
          "text": "x := [1,1]",
          "location": {
            "row": 1,
            "col": 1
          }
        },
        {
          "value": 1,
          "text": "x[_]",
          "location": {
            "row": 1,
            "col": 13
          }
        }
      ],
      "bindings": {
        "x": [
          1,
          1
        ]
      }
    }
  ]
}
torin:~$ opa eval -t rego 'x := [1,1]; x[_]'
{
  "result": [
    {
      "expressions": [
        {
          "value": true,
          "text": "x := [1,1]",
          "location": {
            "row": 1,
            "col": 1
          }
        },
        {
          "value": 1,
          "text": "x[_]",
          "location": {
            "row": 1,
            "col": 13
          }
        }
      ],
      "bindings": {
        "x": [
          1,
          1
        ]
      }
    },
    {
      "expressions": [
        {
          "value": true,
          "text": "x := [1,1]",
          "location": {
            "row": 1,
            "col": 1
          }
        },
        {
          "value": 1,
          "text": "x[_]",
          "location": {
            "row": 1,
            "col": 13
          }
        }
      ],
      "bindings": {
        "x": [
          1,
          1
        ]
      }
    }
  ]
}

OPA version:

$ opa version
Version: 0.28.0-dev
Build Commit: 1d747866
Build Timestamp: 2021-03-16T20:40:39Z
Build Hostname: bigbox.localdomain
Go Version: go1.15.2
WebAssembly: available

Not sure if this one can be traced back to the rego package or if it's happening deeper. E.g., I think we use the opa_set_t implementation from the C library for the results...are the results getting deduped? Technically the query results are sets though so perhaps we don't treat this as a bug...

EDIT: Didn't mean to re-open.

[srenatus]

💭 Hmm. So, we'll definitely call result set add, and that will call opa_set_add,

opa/internal/compiler/wasm/wasm.go

Lines 930 to 933 in 1d74786

	case *ir.ResultSetAdd:
	instrs = append(instrs, instruction.GetLocal{Index: c.lrs})
	instrs = append(instrs, instruction.GetLocal{Index: c.local(stmt.Value)})
	instrs = append(instrs, instruction.Call{Index: c.function(opaSetAdd)})

which then deduplicates:

opa/wasm/src/value.c

Lines 1477 to 1480 in bd5c572

	if (opa_value_compare(curr->v, v) == 0)
	{
	return;
	}

I suppose we could start a list of known differences that we're not going to address (at least not right away). This one and #3252 are on my radar so far...