Symbol Graphs Lack Operators

[SDGGiesbrecht]

Describe the bug

Generated symbol graphs do not contain information about operators.

Steps To Reproduce

Package source files:

// swift-tools-version: 5.6
// Package.swift

import PackageDescription

let package = Package(
  name: "Experiment",
  products: [
    .library(
      name: "Experiment",
      targets: ["Experiment"]
    ),
  ],
  targets: [
    .target(
      name: "Experiment"
    ),
  ]
)

// Sources/Experiment/Experiment.swift
precedencegroup CustomPrecedence {}
infix operator ≠: CustomPrecedence

Terminal command:

package dump-symbol-graph

Result:

{
  "metadata": {
    "formatVersion": {
      "major":0,
      "minor":5,
      "patch":3
    },
   "generator": "Apple Swift version 5.6.1 (swiftlang-5.6.0.323.66 clang-1316.0.20.12)"
  },
  "module": {
    "name": "Experiment",
    "platform": {
      "architecture":"x86_64","vendor":"apple",
      "operatingSystem": {
        "name": "macosx",
        "minimumVersion": {
          "major":10,
          "minor":10,
          "patch":0
        }
      }
    }
  },
  "symbols": [],
  "relationships":[]
}

Expected behavior

There ought to be some sort of entry for CustomPrecedence and ≠.

[franklinsch]

operator and precedencegroup declarations are implicitly public, so yes, I'd expect them to be in the symbol graph. cc @QuietMisdreavus

[QuietMisdreavus]

We currently don't emit symbols for operator declarations themselves, only their implementations on types. I would be curious how a declaration like this could be used in a dependent package. Can someone import Experiment and implement the ≠ operator on their own type with the infix/precedence declarations given in their dependency?

As far as the symbol graph is concerned, what kind of information is necessary to include about an operator/precedence-group declaration? I didn't know about custom precedence groups before.

[tayloraswift]

from tspl:

    precedencegroup precedence group name {
        higherThan: lower group names
        lowerThan: higher group names
        associativity: associativity
        assignment: assignment
    }

the higherThan/lowerThan fields are edge relations, which means we would probably need to emit the standard precedence groups as well.

i think to get started though, it should be enough to just emit a stub for each custom precedence group indicating its existence, which would allow us to attach documentation to it.

[SDGGiesbrecht]

Can someone import Experiment and implement the ≠ operator on their own type with the infix/precedence declarations given in their dependency?

Yes. A client can declare its own operators in an imported precedence group, and can declare its own functions for an imported operator.

I didn't know about custom precedence groups before.

For details, see here.

what kind of information is necessary to include about an operator/precedence-group declaration?

As a rough initial sketch... (and not necessarily implemented all at once)

The declaration used for SymbolGraph.Symbol.names.subHeading and so on should retain the following:

• fixity (prefix/infix/suffix)
• associativity (none, left, right)
• assignment (false/true)

The following should become new cases of SymbolGraph.Relationship.Kind:

• implementsOperator (func → operator)
• hasPrecedence (operator → precedencegroup)
• evaluatedBefore (higherThan/lowerThan; precedencegroup → precedencegroup)

Any documentation comments should also be gathered.