From e259955809dfee520ba0bcc71899be9c471616dd Mon Sep 17 00:00:00 2001
From: Graham Esau <gesau@hotmail.co.uk>
Date: Sun, 17 May 2020 16:41:19 +0100
Subject: [PATCH] Attribute for defining examples (#23)

---
 schemars/tests/examples.rs            | 25 +++++++++++++++++
 schemars/tests/expected/examples.json | 39 +++++++++++++++++++++++++++
 schemars_derive/src/attr/mod.rs       |  8 +++++-
 schemars_derive/src/metadata.rs       | 19 +++++++++++--
 4 files changed, 88 insertions(+), 3 deletions(-)
 create mode 100644 schemars/tests/examples.rs
 create mode 100644 schemars/tests/expected/examples.json

diff --git a/schemars/tests/examples.rs b/schemars/tests/examples.rs
new file mode 100644
index 0000000..7ebca58
--- /dev/null
+++ b/schemars/tests/examples.rs
@@ -0,0 +1,25 @@
+mod util;
+use schemars::JsonSchema;
+use serde::Serialize;
+use util::*;
+
+#[derive(Default, Debug, JsonSchema, Serialize)]
+#[schemars(example = "Struct::default", example = "null")]
+pub struct Struct {
+    #[schemars(example = "eight", example = "null")]
+    foo: i32,
+    bar: bool,
+    #[schemars(example = "null")]
+    baz: Option<&'static str>,
+}
+
+fn eight() -> i32 {
+    8
+}
+
+fn null() -> () {}
+
+#[test]
+fn examples() -> TestResult {
+    test_default_generated_schema::<Struct>("examples")
+}
diff --git a/schemars/tests/expected/examples.json b/schemars/tests/expected/examples.json
new file mode 100644
index 0000000..8df965d
--- /dev/null
+++ b/schemars/tests/expected/examples.json
@@ -0,0 +1,39 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Struct",
+  "examples": [
+    {
+      "bar": false,
+      "baz": null,
+      "foo": 0
+    },
+    null
+  ],
+  "type": "object",
+  "required": [
+    "bar",
+    "foo"
+  ],
+  "properties": {
+    "bar": {
+      "type": "boolean"
+    },
+    "baz": {
+      "examples": [
+        null
+      ],
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "foo": {
+      "examples": [
+        8,
+        null
+      ],
+      "type": "integer",
+      "format": "int32"
+    }
+  }
+}
\ No newline at end of file
diff --git a/schemars_derive/src/attr/mod.rs b/schemars_derive/src/attr/mod.rs
index 4957e1c..9bf221c 100644
--- a/schemars_derive/src/attr/mod.rs
+++ b/schemars_derive/src/attr/mod.rs
@@ -16,7 +16,7 @@ pub struct Attrs {
     pub title: Option<String>,
     pub description: Option<String>,
     pub deprecated: bool,
-    // TODO pub example: Option<syn::Path>,
+    pub examples: Vec<syn::Path>,
 }
 
 #[derive(Debug)]
@@ -111,6 +111,12 @@ impl Attrs {
                     }
                 }
 
+                Meta(NameValue(m)) if m.path.is_ident("example") => {
+                    if let Ok(fun) = parse_lit_into_path(errors, attr_type, "example", &m.lit) {
+                        self.examples.push(fun)
+                    }
+                }
+
                 Meta(_meta_item) => {
                     // TODO uncomment this for 0.8.0 (breaking change)
                     //  https://github.com/GREsau/schemars/issues/18
diff --git a/schemars_derive/src/metadata.rs b/schemars_derive/src/metadata.rs
index 4724223..3f616ee 100644
--- a/schemars_derive/src/metadata.rs
+++ b/schemars_derive/src/metadata.rs
@@ -3,13 +3,14 @@ use attr::Attrs;
 use proc_macro2::{Ident, Span, TokenStream};
 use quote::{ToTokens, TokenStreamExt};
 
-#[derive(Debug, Clone, Default)]
+#[derive(Debug, Clone)]
 pub struct SchemaMetadata<'a> {
     pub title: Option<&'a str>,
     pub description: Option<&'a str>,
     pub deprecated: bool,
     pub read_only: bool,
     pub write_only: bool,
+    pub examples: &'a [syn::Path],
     pub default: Option<TokenStream>,
 }
 
@@ -36,7 +37,10 @@ impl<'a> SchemaMetadata<'a> {
             title: attrs.title.as_ref().and_then(none_if_empty),
             description: attrs.description.as_ref().and_then(none_if_empty),
             deprecated: attrs.deprecated,
-            ..Default::default()
+            examples: &attrs.examples,
+            read_only: false,
+            write_only: false,
+            default: None,
         }
     }
 
@@ -80,6 +84,17 @@ impl<'a> SchemaMetadata<'a> {
             });
         }
 
+        if !self.examples.is_empty() {
+            let examples = self.examples.iter().map(|eg| {
+                quote! {
+                    schemars::_serde_json::value::to_value(#eg())
+                }
+            });
+            setters.push(quote! {
+                metadata.examples = vec![#(#examples),*].into_iter().flatten().collect();
+            });
+        }
+
         if let Some(default) = &self.default {
             setters.push(quote! {
                 metadata.default = #default.and_then(|d| schemars::_serde_json::value::to_value(d).ok());