fix(schema): honor single-entry patternProperties as additionalProperties

packages/quicktype-core/src/input/JSONSchemaInput.ts

@@ -1139,14 +1139,20 @@ async function addTypesInSchema(
             }
 
             let additionalProperties = schema.additionalProperties;
-            // This is an incorrect hack to fix an issue with a Go->Schema generator:
-            // https://github.com/quicktype/quicktype/issues/976
+            // Treat a single pattern property as additional properties since
+            // per-pattern typed properties aren't supported.
             if (
                 additionalProperties === undefined &&
                 typeof schema.patternProperties === "object" &&
-                hasOwnProperty(schema.patternProperties, ".*")
+                schema.patternProperties !== null
             ) {
-                additionalProperties = schema.patternProperties[".*"];
+                const patterns = Object.getOwnPropertyNames(
+                    schema.patternProperties,
+                );
+                if (patterns.length === 1) {
+                    additionalProperties =
+                        schema.patternProperties[patterns[0]];
+                }
             }
 
             // Handle unevaluatedProperties if additionalProperties is not defined

test/inputs/schema/pattern-properties.1.fail.json

@@ -0,0 +1,8 @@
+{
+  "alternators": {
+    "1": {
+      "voltage": "not a number",
+      "name": "Main alternator"
+    }
+  }
+}

test/inputs/schema/pattern-properties.1.json

@@ -0,0 +1,12 @@
+{
+  "alternators": {
+    "1": {
+      "voltage": 14.2,
+      "name": "Main alternator"
+    },
+    "backup": {
+      "voltage": 13.8,
+      "name": "Backup alternator"
+    }
+  }
+}

test/inputs/schema/pattern-properties.schema

@@ -0,0 +1,19 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Electrical",
+  "type": "object",
+  "properties": {
+    "alternators": {
+      "type": "object",
+      "patternProperties": {
+        "(^[A-Za-z0-9]+$)": {
+          "type": "object",
+          "properties": {
+            "voltage": { "type": "number" },
+            "name": { "type": "string" }
+          }
+        }
+      }
+    }
+  }
+}

test/languages.ts

@@ -55,6 +55,7 @@ const skipsUntypedUnions = [
 // schema whose fail sample relies on rejecting a mistyped map value.
 const skipsMapValueValidation = [
     "go-schema-pattern-properties.schema",
+    "pattern-properties.schema",
     "unevaluated-properties.schema",
 ];