encoding/jsonschema: do not generate defaults

The `default` keyword in JSON Schema should be an annotation,
not a constraint, and in general schemas in CUE should be pure,
so having the defaults in there seems wrong, especially as:

- it precludes people from adding their own defaults
- defaults don't work when they're inside `matchN` calls
- defaults will not work as expected inside optional or required fields,
which are the only kind of fields that encoding/jsonschema produces.

In the future, we might wish to provide template-like values
that do include defaults (that's issue #3473), but for now, this keeps things simple
and avoids issues with collisions with defaults in user code.

So we remove support for `default`, and also remove the unused code
for `examples`: we can add it back later in the same or another form
as desired.

Fixes #3472

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I544734d3361c7b2eff410dae8f27d831ec8c0e97
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1207146
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

encoding/jsonschema/constraints_generic.go

@@ -50,11 +50,8 @@ func constraintConst(key string, n cue.Value, s *state) {
 }
 
 func constraintDefault(key string, n cue.Value, s *state) {
-	sc := *s
-	s.default_ = sc.value(n)
-	// TODO: must validate that the default is subsumed by the normal value,
-	// as CUE will otherwise broaden the accepted values with the default.
-	s.examples = append(s.examples, s.default_)
+	// TODO make the default value available in a separate
+	// template-like CUE value outside of the usual schema output.
 }
 
 func constraintDeprecated(key string, n cue.Value, s *state) {
@@ -90,12 +87,6 @@ func constraintExamples(key string, n cue.Value, s *state) {
 	if n.Kind() != cue.ListKind {
 		s.errf(n, `value of "examples" must be an array, found %v`, n.Kind())
 	}
-	// TODO: implement examples properly.
-	// for _, n := range s.listItems("examples", n, true) {
-	// 	if ex := s.value(n); !isAny(ex) {
-	// 		s.examples = append(s.examples, ex)
-	// 	}
-	// }
 }
 
 func constraintNullable(key string, n cue.Value, s *state) {

encoding/jsonschema/decode.go

@@ -451,8 +451,6 @@ type state struct {
 	all      constraintInfo // values and oneOf etc.
 	nullable *ast.BasicLit  // nullable
 
-	default_     ast.Expr
-	examples     []ast.Expr
 	exclusiveMin bool // For OpenAPI and legacy support.
 	exclusiveMax bool // For OpenAPI and legacy support.
 
@@ -680,19 +678,6 @@ func (s *state) finalize() (e ast.Expr) {
 		a = []ast.Expr{s.nullable, e}
 	}
 
-outer:
-	switch {
-	case s.default_ != nil:
-		// check conditions where default can be skipped.
-		switch x := s.default_.(type) {
-		case *ast.ListLit:
-			if s.allowedTypes == cue.ListKind && len(x.Elts) == 0 {
-				break outer
-			}
-		}
-		a = append(a, &ast.UnaryExpr{Op: token.MUL, X: s.default_})
-	}
-
 	e = ast.NewBinExpr(token.OR, a...)
 
 	if len(s.definitions) > 0 {

encoding/jsonschema/external_teststats.txt

@@ -1,13 +1,13 @@
 # Generated by CUE_UPDATE=1 go test. DO NOT EDIT
 v2:
 	schema extract (pass / total): 1054 / 1363 = 77.3%
-	tests (pass / total): 3788 / 4803 = 78.9%
-	tests on extracted schemas (pass / total): 3788 / 3955 = 95.8%
+	tests (pass / total): 3793 / 4803 = 79.0%
+	tests on extracted schemas (pass / total): 3793 / 3955 = 95.9%
 
 v3:
 	schema extract (pass / total): 1054 / 1363 = 77.3%
-	tests (pass / total): 3778 / 4803 = 78.7%
-	tests on extracted schemas (pass / total): 3778 / 3955 = 95.5%
+	tests (pass / total): 3783 / 4803 = 78.8%
+	tests on extracted schemas (pass / total): 3783 / 3955 = 95.7%
 
 Optional tests
 

encoding/jsonschema/testdata/external/tests/draft2019-09/default.json

@@ -78,11 +78,7 @@
 				"data": {
 					"alpha": 5
 				},
-				"valid": false,
-				"skip": {
-					"v2": "unexpected success",
-					"v3": "unexpected success"
-				}
+				"valid": false
 			},
 			{
 				"description": "missing properties are not filled in with the default",

encoding/jsonschema/testdata/external/tests/draft2020-12/default.json

@@ -78,11 +78,7 @@
 				"data": {
 					"alpha": 5
 				},
-				"valid": false,
-				"skip": {
-					"v2": "unexpected success",
-					"v3": "unexpected success"
-				}
+				"valid": false
 			},
 			{
 				"description": "missing properties are not filled in with the default",

encoding/jsonschema/testdata/external/tests/draft4/default.json

@@ -75,11 +75,7 @@
 				"data": {
 					"alpha": 5
 				},
-				"valid": false,
-				"skip": {
-					"v2": "unexpected success",
-					"v3": "unexpected success"
-				}
+				"valid": false
 			},
 			{
 				"description": "missing properties are not filled in with the default",

encoding/jsonschema/testdata/external/tests/draft6/default.json

@@ -75,11 +75,7 @@
 				"data": {
 					"alpha": 5
 				},
-				"valid": false,
-				"skip": {
-					"v2": "unexpected success",
-					"v3": "unexpected success"
-				}
+				"valid": false
 			},
 			{
 				"description": "missing properties are not filled in with the default",

encoding/jsonschema/testdata/external/tests/draft7/default.json

@@ -75,11 +75,7 @@
 				"data": {
 					"alpha": 5
 				},
-				"valid": false,
-				"skip": {
-					"v2": "unexpected success",
-					"v3": "unexpected success"
-				}
+				"valid": false
 			},
 			{
 				"description": "missing properties are not filled in with the default",

encoding/jsonschema/testdata/txtar/type.txtar

@@ -37,9 +37,6 @@ close({
 	intString?: null | bool | int | string | [...]
 	object?: {
 		...
-	} | *{
-		foo: "bar"
-		baz: 1.3
 	}
-	numOrList?: matchN(1, [number, [...number]]) | *[1, 2, 3]
+	numOrList?: matchN(1, [number, [...number]])
 })