cue: Expr handles empty lists to or/and builtins

Reflect semantics of builtins, which translate empty lists
to an error or top, respectively.

Fixes #1234

Signed-off-by: Marcel van Lohuizen <mpvl@golang.org>

Change-Id: I9cb3fd242f9ccfa86213fee198125617c1d68dcf
Signed-off-by: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/527312
Unity-Result: CUEcueckoo <cueckoo@cuelang.org>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Paul Jolly <paul@myitcv.io>

Author: mpvl

cue/types.go

@@ -2370,6 +2370,20 @@ func (v Value) Expr() (Op, []Value) {
 			if fn.Name == "and" {
 				op = AndOp
 			}
+
+			if len(a) == 0 {
+				// Mimic semantics of builtin.
+				switch op {
+				case AndOp:
+					a = append(a, remakeValue(v, env, &adt.Top{}))
+				case OrOp:
+					a = append(a, remakeValue(v, env, &adt.Bottom{
+						Code: adt.IncompleteError,
+						Err:  errors.Newf(x.Src.Fun.Pos(), "empty list in call to or"),
+					}))
+				}
+				op = NoOp
+			}
 			break
 		}
 		a = append(a, remakeValue(v, env, x.Fun))

cue/types_test.go

@@ -3351,13 +3351,20 @@ func TestExpr(t *testing.T) {
 		want:  `&({c:a} {b:a})`,
 	}, {
 		input: `v: [...number] | *[1, 2, 3]`,
-		want:  `([...number]|*[1,2,3])`,
+		// Filter defaults that are subsumed by another value.
+		want: `[...number]`,
 	}, {
 		input: `v: or([1, 2, 3])`,
 		want:  `|(1 2 3)`,
+	}, {
+		input: `v: or([])`,
+		want:  `_|_(empty list in call to or)`,
 	}, {
 		input: `v: and([1, 2, 3])`,
 		want:  `&(1 2 3)`,
+	}, {
+		input: `v: and([])`,
+		want:  `_`,
 	}}
 	for _, tc := range testCases {
 		t.Run(tc.input, func(t *testing.T) {
@@ -3373,7 +3380,7 @@ func TestExpr(t *testing.T) {
 func exprStr(v Value) string {
 	op, operands := v.Expr()
 	if op == NoOp {
-		return compactRawStr(v)
+		return compactRawStr(operands[0])
 	}
 	s := op.String()
 	s += "("

encoding/openapi/openapi_test.go

@@ -217,20 +217,36 @@ func walk(om *openapi.OrderedMap) {
 	}
 }
 
+// TODO: move OpenAPI testing to txtar and allow errors.
+func TestIssue1234(t *testing.T) {
+	var r cue.Runtime
+	inst, err := r.Compile("test", `
+#Test: or([])
+
+	`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = openapi.Gen(inst, &openapi.Config{})
+	if err == nil {
+		t.Fatal("expected error")
+	}
+}
+
 // This is for debugging purposes. Do not remove.
 func TestX(t *testing.T) {
 	t.Skip()
 
 	var r cue.Runtime
 	inst, err := r.Compile("test", `
-	AnyField: "any value"
 	`)
 	if err != nil {
 		t.Fatal(err)
 	}
 
 	b, err := openapi.Gen(inst, &openapi.Config{
-		ExpandReferences: true,
+		// ExpandReferences: true,
 	})
 	if err != nil {
 		t.Fatal(errors.Details(err, nil))