Fix deriving JsonSchema inside macro (#79)

schemars/tests/expected/macro_built_struct.json

@@ -0,0 +1,20 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "A",
+  "type": "object",
+  "required": [
+    "v",
+    "x"
+  ],
+  "properties": {
+    "x": {
+      "type": "integer",
+      "format": "uint8",
+      "minimum": 0.0
+    },
+    "v": {
+      "type": "integer",
+      "format": "int32"
+    }
+  }
+}

schemars/tests/macro.rs

@@ -0,0 +1,22 @@
+mod util;
+use schemars::JsonSchema;
+use util::*;
+
+macro_rules! build_struct {
+    (
+        $id:ident { $($t:tt)* }
+    ) => {
+        #[derive(Debug, JsonSchema)]
+        pub struct $id {
+            x: u8,
+            $($t)*
+        }
+    };
+}
+
+build_struct!(A { v: i32 });
+
+#[test]
+fn macro_built_struct() -> TestResult {
+    test_default_generated_schema::<A>("macro_built_struct")
+}