encoding/openapi: regression vs evalv2 where additionalProperties and defaults are no longer produced

[myitcv]

What version of CUE are you using (cue version)?

$ cue version
cue version v0.0.0-20250203094823-0265d7d62829

go version go1.23.5
      -buildmode exe
       -compiler gc
  DefaultGODEBUG asynctimerchan=1,gotypesalias=0,httpservecontentkeepheaders=1,tls3des=1,tlskyber=0,x509keypairleaf=0,x509negativeserial=1
     CGO_ENABLED 1
          GOARCH arm64
            GOOS linux
         GOARM64 v8.0
             vcs git
    vcs.revision 0265d7d62829c1002e3ea58dd6c5b992fea5f2e3
        vcs.time 2025-02-03T09:48:23Z
    vcs.modified false
cue.lang.version v0.13.0

Does this issue reproduce with the latest release?

Yes

What did you do?

go mod edit -replace=cuelang.org/go=/home/myitcv/dev/cuelang/cue
go mod tidy

# -- evalv2 --
env CUE_EXPERIMENT=evalv3=0

# Go API
exec go mod tidy
exec go run main.go
cmp stdout stdout.golden

# -- evalv3 --
env CUE_EXPERIMENT=evalv3=1

# Go API
exec go mod tidy
exec go run main.go
cmp stdout stdout.golden

-- go.mod --
module mod.example
-- deps.go --
package deps
import _ "cuelang.org/go/cmd/cue"
-- types.cue --
package openapi

#Tags: {
    owner: string | *"sre"
    role: string | *"control-plane"
    ...
}

#Spec: {
    name: string
    tags?: #Tags | *#Tags
}

-- go.mod --
module example.com/openapi

go 1.23

require cuelang.org/go v0.12.0

-- main.go --
package main

import (
	"bytes"
	"fmt"
	"log"
	"os"
	"encoding/json"

	"cuelang.org/go/cue/cuecontext"
	"cuelang.org/go/encoding/openapi"
)

func run() error {
	runtime := cuecontext.New()

	contents, err := os.ReadFile("types.cue")
	if err != nil {
	    return err
	}

	val := runtime.CompileString(string(contents))
	if val.Err() != nil {
		return val.Err()
	}

	b, err := openapi.Gen(val, &openapi.Config{
		Info: map[string]any{
			"title":       "XRD schemas",
			"description": "general",
			"version":     "0.1.0",
		},
		ExpandReferences: true,
	})
	if err != nil {
		return err
	}
	var res bytes.Buffer
	err = json.Indent(&res, b, "", "  ")
	if err != nil {
		return err
	}
	fmt.Println(res.String())
	return nil
}

func main() {
	if err := run(); err != nil {
		log.Fatalln(err)
	}
}
-- stdout.golden --
{
  "openapi": "3.0.0",
  "info": {
    "description": "general",
    "title": "XRD schemas",
    "version": "0.1.0"
  },
  "paths": {},
  "components": {
    "schemas": {
      "Spec": {
        "type": "object",
        "required": [
          "name"
        ],
        "properties": {
          "name": {
            "type": "string"
          },
          "tags": {
            "type": "object",
            "required": [
              "owner",
              "role"
            ],
            "properties": {
              "owner": {
                "type": "string",
                "default": "sre"
              },
              "role": {
                "type": "string",
                "default": "control-plane"
              }
            },
            "additionalProperties": {}
          }
        }
      },
      "Tags": {
        "type": "object",
        "required": [
          "owner",
          "role"
        ],
        "properties": {
          "owner": {
            "type": "string",
            "default": "sre"
          },
          "role": {
            "type": "string",
            "default": "control-plane"
          }
        },
        "additionalProperties": {}
      }
    }
  }
}

What did you expect to see?

Passing test.

What did you see instead?

# -- evalv2 -- (0.000s)
# Go API (0.319s)
# -- evalv3 -- (0.000s)
# Go API (0.305s)
> exec go mod tidy
> exec go run main.go
[stdout]
{
  "openapi": "3.0.0",
  "info": {
    "description": "general",
    "title": "XRD schemas",
    "version": "0.1.0"
  },
  "paths": {},
  "components": {
    "schemas": {
      "Spec": {
        "type": "object",
        "required": [
          "name"
        ],
        "properties": {
          "name": {
            "type": "string"
          },
          "tags": {
            "type": "object",
            "required": [
              "owner",
              "role"
            ],
            "properties": {
              "owner": {
                "type": "string",
                "default": "sre"
              },
              "role": {
                "type": "string",
                "default": "control-plane"
              }
            },
            "default": {
              "owner": "sre",
              "role": "control-plane"
            }
          }
        }
      },
      "Tags": {
        "type": "object",
        "required": [
          "owner",
          "role"
        ],
        "properties": {
          "owner": {
            "type": "string",
            "default": "sre"
          },
          "role": {
            "type": "string",
            "default": "control-plane"
          }
        }
      }
    }
  }
}
> cmp stdout stdout.golden
diff stdout stdout.golden
--- stdout
+++ stdout.golden
@@ -33,10 +33,7 @@
                 "default": "control-plane"
               }
             },
-            "default": {
-              "owner": "sre",
-              "role": "control-plane"
-            }
+            "additionalProperties": {}
           }
         }
       },
@@ -55,7 +52,8 @@
             "type": "string",
             "default": "control-plane"
           }
-        }
+        },
+        "additionalProperties": {}
       }
     }
   }

FAIL: /tmp/testscript515885163/repro.txtar/script.txtar:18: stdout and stdout.golden differ
error running repro.txtar in /tmp/testscript515885163/repro.txtar

It's highly likely that the missing additionalProperites is related to #3720.

The missing defaults could well be a function of the work that @rogpeppe did regarding defaults and JSON Schema.

[rogpeppe]

The missing defaults could well be a function of the work that @rogpeppe did regarding defaults and JSON Schema.

At first glance that seems unlikely, as the code above is generating OpenAPI from CUE but encoding/jsonschema is only concerned with generating CUE from JSON Schema/OpenAPI, at least for now.