encoding/jsonschema: better "type excluded" logic

Currently, the error "constraint not allowed because type xxx is
excluded" is produced when there is a constraint for a given kind and
the type is known to be disallowed. However, types are not exclusive in
this way in JSONSchema.

Instead, produce an error only when _all_ types are known to be excluded
which, although technically still not an error, is much less likely to
result in a real-world schema being rejected.

Fixes #393.

Signed-off-by: Roger Peppe <[email protected]>
Change-Id: I45b4a7fa540ba537f2e2dbfe973782474be280d5
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1199308
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>

Author: rogpeppe

encoding/jsonschema/decode.go

@@ -433,40 +433,62 @@ func (s *state) finalize() (e ast.Expr) {
 		return !ok
 	})
 
+	type excludeInfo struct {
+		pos      token.Pos
+		typIndex int
+	}
+	var excluded []excludeInfo
+	npossible := 0
+	nexcluded := 0
 	for i, t := range s.types {
 		k := coreToCUE[i]
 		isAllowed := s.allowedTypes&k != 0
 		if len(t.constraints) > 0 {
+			npossible++
 			if t.typ == nil && !isAllowed {
+				// TODO this implies a redundant constraint, which is technically allowed,
+				// but in practice probably represents a mistake. We could provide
+				// a mode that warns about such likely errors.
+				nexcluded++
 				for _, c := range t.constraints {
-					s.addErr(errors.Newf(c.Pos(),
-						"constraint not allowed because type %s is excluded",
-						coreTypeName[i],
-					))
+					excluded = append(excluded, excludeInfo{c.Pos(), i})
 				}
 				continue
 			}
 			x := ast.NewBinExpr(token.AND, t.constraints...)
 			disjuncts = append(disjuncts, x)
 		} else if s.usedTypes&k != 0 {
+			npossible++
 			continue
 		} else if t.typ != nil {
+			npossible++
 			if !isAllowed {
-				s.addErr(errors.Newf(t.typ.Pos(),
-					"constraint not allowed because type %s is excluded",
-					coreTypeName[i],
-				))
+				// TODO this implies a redundant type constraint, which is technically allowed,
+				// but in practice probably represents a mistake. We could provide
+				// a mode that warns about such likely errors.
+				nexcluded++
+				excluded = append(excluded, excludeInfo{t.typ.Pos(), i})
 				continue
 			}
 			disjuncts = append(disjuncts, t.typ)
 		} else if types&k != 0 {
+			npossible++
 			x := kindToAST(k)
 			if x != nil {
 				disjuncts = append(disjuncts, x)
 			}
 		}
 	}
-
+	if nexcluded == npossible {
+		// All possibilities have been excluded: this is an impossible
+		// schema.
+		for _, e := range excluded {
+			s.addErr(errors.Newf(e.pos,
+				"constraint not allowed because type %s is excluded",
+				coreTypeName[e.typIndex],
+			))
+		}
+	}
 	conjuncts = append(conjuncts, s.all.constraints...)
 
 	obj := s.obj

encoding/jsonschema/testdata/typeexcluded.txtar

@@ -103,26 +103,32 @@
     }
   }
 }
--- out/decode/err --
-constraint not allowed because type string is excluded:
-    type.json:10:7
-constraint not allowed because type array is excluded:
-    type.json:18:9
-constraint not allowed because type bool is excluded:
-    type.json:19:9
-constraint not allowed because type number is excluded:
-    type.json:20:9
-constraint not allowed because type object is excluded:
-    type.json:21:9
-constraint not allowed because type null is excluded:
-    type.json:23:9
-constraint not allowed because type object is excluded:
-    type.json:32:7
-constraint not allowed because type string is excluded:
-    type.json:44:7
-constraint not allowed because type array is excluded:
-    type.json:51:9
-constraint not allowed because type string is excluded:
-    type.json:64:7
-constraint not allowed because type bool is excluded:
-    type.json:68:9
+-- out/decode/cue --
+import (
+	"list"
+	"strings"
+)
+
+e0?: int & >=2 & <=3
+e1?: "cover" | "contain"
+
+// none
+e2?: "none"
+e3?: list.UniqueItems() & [_, ...] & [...strings.MinRunes(1)]
+
+// Main authors of the plugin
+e4?: [...string]
+e5?: int & >=0
+e6?: [...=~"^[A-Za-z0-9 _.-]+$"]
+e7?: (true | {
+	...
+} | {
+	disableFix?: bool
+	...
+} & {
+	ignoreMediaFeatureNames?: list.UniqueItems() & [_, ...] & [...string]
+	...
+}) & {
+	...
+}
+...