Add transform = ... attribute (#312)

This allows running arbitrary transforms on generated schemas when deriving `JsonSchema`

schemars/tests/expected/transform_enum_external.json

@@ -0,0 +1,25 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "title": "External",
+  "oneOf": [
+    {
+      "type": "string",
+      "const": "Unit",
+      "propertyCount": 0,
+      "upperType": "STRING"
+    },
+    {
+      "type": "object",
+      "properties": {
+        "NewType": true
+      },
+      "required": [
+        "NewType"
+      ],
+      "additionalProperties": false,
+      "propertyCount": 1,
+      "upperType": "OBJECT"
+    }
+  ],
+  "propertyCount": 0
+}

schemars/tests/expected/transform_struct.json

@@ -0,0 +1,20 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "title": "Struct",
+  "type": "object",
+  "properties": {
+    "value": true,
+    "int": {
+      "type": "integer",
+      "format": "int32",
+      "propertyCount": 0,
+      "upperType": "INTEGER"
+    }
+  },
+  "required": [
+    "value",
+    "int"
+  ],
+  "upperType": "OBJECT",
+  "propertyCount": 2
+}

schemars/tests/extend.rs

@@ -17,7 +17,7 @@ struct Struct {
 }
 
 #[test]
-fn doc_comments_struct() -> TestResult {
+fn extend_struct() -> TestResult {
     test_default_generated_schema::<Struct>("extend_struct")
 }
 
@@ -36,7 +36,7 @@ enum External {
 }
 
 #[test]
-fn doc_comments_enum_external() -> TestResult {
+fn extend_enum_external() -> TestResult {
     test_default_generated_schema::<External>("extend_enum_external")
 }
 
@@ -53,7 +53,7 @@ enum Internal {
 }
 
 #[test]
-fn doc_comments_enum_internal() -> TestResult {
+fn extend_enum_internal() -> TestResult {
     test_default_generated_schema::<Internal>("extend_enum_internal")
 }
 
@@ -72,7 +72,7 @@ enum Untagged {
 }
 
 #[test]
-fn doc_comments_enum_untagged() -> TestResult {
+fn extend_enum_untagged() -> TestResult {
     test_default_generated_schema::<Untagged>("extend_enum_untagged")
 }
 
@@ -91,6 +91,6 @@ enum Adjacent {
 }
 
 #[test]
-fn doc_comments_enum_adjacent() -> TestResult {
+fn extend_enum_adjacent() -> TestResult {
     test_default_generated_schema::<Adjacent>("extend_enum_adjacent")
 }

schemars/tests/transform.rs

@@ -0,0 +1,51 @@
+mod util;
+use schemars::{transform::RecursiveTransform, JsonSchema, Schema};
+use serde_json::Value;
+use util::*;
+
+fn capitalize_type(schema: &mut Schema) {
+    if let Some(obj) = schema.as_object_mut() {
+        if let Some(Value::String(ty)) = obj.get("type") {
+            obj.insert("upperType".to_owned(), ty.to_uppercase().into());
+        }
+    }
+}
+
+fn insert_property_count(schema: &mut Schema) {
+    if let Some(obj) = schema.as_object_mut() {
+        let count = obj
+            .get("properties")
+            .and_then(|p| p.as_object())
+            .map_or(0, |p| p.len());
+        obj.insert("propertyCount".to_owned(), count.into());
+    }
+}
+
+#[allow(dead_code)]
+#[derive(JsonSchema)]
+#[schemars(transform = RecursiveTransform(capitalize_type), transform = insert_property_count)]
+struct Struct {
+    value: Value,
+    #[schemars(transform = insert_property_count)]
+    int: i32,
+}
+
+#[test]
+fn transform_struct() -> TestResult {
+    test_default_generated_schema::<Struct>("transform_struct")
+}
+
+#[allow(dead_code)]
+#[derive(JsonSchema)]
+#[schemars(transform = RecursiveTransform(capitalize_type), transform = insert_property_count)]
+enum External {
+    #[schemars(transform = insert_property_count)]
+    Unit,
+    #[schemars(transform = insert_property_count)]
+    NewType(Value),
+}
+
+#[test]
+fn transform_enum_external() -> TestResult {
+    test_default_generated_schema::<External>("transform_enum_external")
+}

schemars/tests/ui/transform_str.rs

@@ -0,0 +1,7 @@
+use schemars::JsonSchema;
+
+#[derive(JsonSchema)]
+#[schemars(transform = "x")]
+pub struct Struct;
+
+fn main() {}

schemars/tests/ui/transform_str.stderr

@@ -0,0 +1,6 @@
+error: Expected a `fn(&mut Schema)` or other value implementing `schemars::transform::Transform`, found `&str`.
+       Did you mean `[schemars(transform = x)]`?
+ --> tests/ui/transform_str.rs:4:24
+  |
+4 | #[schemars(transform = "x")]
+  |                        ^^^