make 'then' blocks transparent by default (#654)

docs/technical/web.md

@@ -85,9 +85,7 @@ Error messages may contain special tokens:
   The child errors themselves may be marked `$transparent`, etc. If an error has no child errors,
   this override is ignored.
 
-Caveats:
-* To override an error from a `then` block, the `@errorMessages` must be inside the `then` block
-  instead of adjacent.
+  Validation errors for `then` blocks are transparent by default, unless overridden.
 
 </dd>
 </dl>

src/SMAPI.Web/Controllers/JsonValidatorController.cs

@@ -213,7 +213,7 @@ namespace StardewModdingAPI.Web.Controllers
         private IEnumerable<JsonValidatorErrorModel> GetErrorModels(ValidationError error)
         {
             // skip through transparent errors
-            if (this.GetOverrideError(error) == this.TransparentToken && error.ChildErrors.Any())
+            if (this.IsTransparentError(error))
             {
                 foreach (var model in error.ChildErrors.SelectMany(this.GetErrorModels))
                     yield return model;
@@ -240,7 +240,7 @@ namespace StardewModdingAPI.Web.Controllers
                 return message;
 
             // skip through transparent errors
-            while (this.GetOverrideError(error) == this.TransparentToken && error.ChildErrors.Count == 1)
+            if (this.IsTransparentError(error))
                 error = error.ChildErrors[0];
 
             // get friendly representation of main error
@@ -266,6 +266,19 @@ namespace StardewModdingAPI.Web.Controllers
             return message;
         }
 
+        /// <summary>Get whether a validation error should be omitted in favor of its child errors in user-facing error messages.</summary>
+        /// <param name="error">The error to check.</param>
+        private bool IsTransparentError(ValidationError error)
+        {
+            if (!error.ChildErrors.Any())
+                return false;
+
+            string @override = this.GetOverrideError(error);
+            return
+                @override == this.TransparentToken
+                || (error.ErrorType == ErrorType.Then && @override == null);
+        }
+
         /// <summary>Get an override error from the JSON schema, if any.</summary>
         /// <param name="error">The schema validation error.</param>
         private string GetOverrideError(ValidationError error)

src/SMAPI.Web/wwwroot/schemas/content-patcher.json

@@ -273,9 +273,6 @@
                             "required": [ "FromFile" ],
                             "propertyNames": {
                                 "enum": [ "Action", "Target", "LogName", "Enabled", "When", "FromFile" ]
-                            },
-                            "@errorMessages": {
-                                "then": "$transparent"
                             }
                         }
                     },
@@ -289,9 +286,6 @@
                             "required": [ "FromFile" ],
                             "propertyNames": {
                                 "enum": [ "Action", "Target", "LogName", "Enabled", "When", "FromFile", "FromArea", "ToArea", "PatchMode" ]
-                            },
-                            "@errorMessages": {
-                                "then": "$transparent"
                             }
                         }
                     },
@@ -304,9 +298,6 @@
                         "then": {
                             "propertyNames": {
                                 "enum": [ "Action", "Target", "LogName", "Enabled", "When", "Fields", "Entries", "MoveEntries" ]
-                            },
-                            "@errorMessages": {
-                                "then": "$transparent"
                             }
                         }
                     },