feat: improve error reporting for bad/missing discriminator (#718)

Author: gward

openapi3/schema.go

@@ -922,16 +922,35 @@ func (schema *Schema) visitSetOperations(settings *schemaValidationSettings, val
 			if valuemap, okcheck := value.(map[string]interface{}); okcheck {
 				discriminatorVal, okcheck := valuemap[pn]
 				if !okcheck {
-					return errors.New("input does not contain the discriminator property")
+					return &SchemaError{
+						Schema:      schema,
+						SchemaField: "discriminator",
+						Reason:      fmt.Sprintf("input does not contain the discriminator property %q", pn),
+					}
 				}
 
 				discriminatorValString, okcheck := discriminatorVal.(string)
 				if !okcheck {
-					return errors.New("descriminator value is not a string")
+					valStr := "null"
+					if discriminatorVal != nil {
+						valStr = fmt.Sprintf("%v", discriminatorVal)
+					}
+
+					return &SchemaError{
+						Value:       discriminatorVal,
+						Schema:      schema,
+						SchemaField: "discriminator",
+						Reason:      fmt.Sprintf("value of discriminator property %q is not a string: %v", pn, valStr),
+					}
 				}
 
 				if discriminatorRef, okcheck = schema.Discriminator.Mapping[discriminatorValString]; len(schema.Discriminator.Mapping) > 0 && !okcheck {
-					return errors.New("input does not contain a valid discriminator value")
+					return &SchemaError{
+						Value:       discriminatorVal,
+						Schema:      schema,
+						SchemaField: "discriminator",
+						Reason:      fmt.Sprintf("discriminator property %q has invalid value: %q", pn, discriminatorVal),
+					}
 				}
 			}
 		}

openapi3/schema_oneOf_test.go

@@ -86,7 +86,7 @@ func TestVisitJSON_OneOf_MissingDiscriptorProperty(t *testing.T) {
 	err = s.Components.Schemas["Animal"].Value.VisitJSON(map[string]interface{}{
 		"name": "snoopy",
 	})
-	require.EqualError(t, err, "input does not contain the discriminator property")
+	require.ErrorContains(t, err, "input does not contain the discriminator property \"$type\"\n")
 }
 
 func TestVisitJSON_OneOf_MissingDiscriptorValue(t *testing.T) {
@@ -96,7 +96,7 @@ func TestVisitJSON_OneOf_MissingDiscriptorValue(t *testing.T) {
 		"name":  "snoopy",
 		"$type": "snake",
 	})
-	require.EqualError(t, err, "input does not contain a valid discriminator value")
+	require.ErrorContains(t, err, "discriminator property \"$type\" has invalid value: \"snake\"")
 }
 
 func TestVisitJSON_OneOf_MissingField(t *testing.T) {
@@ -126,14 +126,14 @@ func TestVisitJSON_OneOf_BadDescriminatorType(t *testing.T) {
 		"scratches": true,
 		"$type":     1,
 	})
-	require.EqualError(t, err, "descriminator value is not a string")
+	require.ErrorContains(t, err, "value of discriminator property \"$type\" is not a string: 1")
 
 	err = s.Components.Schemas["Animal"].Value.VisitJSON(map[string]interface{}{
 		"name":  "snoopy",
 		"barks": true,
 		"$type": nil,
 	})
-	require.EqualError(t, err, "descriminator value is not a string")
+	require.ErrorContains(t, err, "value of discriminator property \"$type\" is not a string: null")
 }
 
 func TestVisitJSON_OneOf_Path(t *testing.T) {