encoding/jsonschema: implement "not"

This change implements the "not" keyword using `matchN`.
No test regressions were encountered when updating the external test data.

One regression was encountered when updating the regular
test data, and filed as a comment under issue #3422.
This required updating the test data to get the test to pass.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: Ib2537af7424895843eebc1b915bc643894637afa

encoding/jsonschema/constraints.go

@@ -88,6 +88,7 @@ var constraints = []*constraint{
 	p2("minLength", constraintMinLength),
 	p3("minimum", constraintMinimum),
 	p2("multipleOf", constraintMultipleOf),
+	p3("not", constraintNot),
 	p3("oneOf", constraintOneOf),
 	p2("nullable", constraintNullable),
 	p2("pattern", constraintPattern),

encoding/jsonschema/constraints_combinator.go

@@ -140,3 +140,15 @@ func constraintOneOf(key string, n cue.Value, s *state) {
 	// TODO: oneOf({a:x}, {b:y}, ..., not(anyOf({a:x}, {b:y}, ...))),
 	// can be translated to {} | {a:x}, {b:y}, ...
 }
+
+func constraintNot(key string, n cue.Value, s *state) {
+	subSchema := s.schema(n)
+	s.all.add(n, ast.NewCall(
+		ast.NewIdent("matchN"),
+		&ast.BasicLit{
+			Kind:  token.INT,
+			Value: "0",
+		},
+		ast.NewList(subSchema),
+	))
+}

encoding/jsonschema/external_teststats.txt

@@ -1,10 +1,10 @@
 # Generated by teststats. DO NOT EDIT
 v2:
-	schema extract (pass / total): 975 / 1637 = 59.6%
-	tests (pass / total): 3140 / 7175 = 43.8%
-	tests on extracted schemas (pass / total): 3140 / 3546 = 88.6%
+	schema extract (pass / total): 1015 / 1637 = 62.0%
+	tests (pass / total): 3308 / 7175 = 46.1%
+	tests on extracted schemas (pass / total): 3308 / 3722 = 88.9%
 
 v3:
-	schema extract (pass / total): 967 / 1637 = 59.1%
-	tests (pass / total): 3074 / 7175 = 42.8%
-	tests on extracted schemas (pass / total): 3074 / 3538 = 86.9%
+	schema extract (pass / total): 1003 / 1637 = 61.3%
+	tests (pass / total): 3214 / 7175 = 44.8%
+	tests on extracted schemas (pass / total): 3214 / 3678 = 87.4%