Set schema title and description from #[doc]s

Work in progress

schemars_derive/src/doc_attrs.rs

@@ -0,0 +1,63 @@
+use syn::{Attribute, Lit::Str, Meta::NameValue, MetaNameValue};
+
+pub fn get_title_and_desc_from_docs(attrs: &[Attribute]) -> (Option<String>, Option<String>) {
+    let docs = match get_docs(attrs) {
+        None => return (None, None),
+        Some(docs) => docs,
+    };
+
+    if docs.starts_with('#') {
+        let mut split = docs.splitn(2, '\n');
+        let title = split
+            .next()
+            .unwrap()
+            .trim_start_matches('#')
+            .trim()
+            .to_owned();
+        let maybe_desc = split.next().map(|s| s.trim().to_owned());
+        (none_if_empty(title), maybe_desc)
+    } else {
+        (None, none_if_empty(docs))
+    }
+}
+
+fn none_if_empty(s: String) -> Option<String> {
+    if s.is_empty() {
+        None
+    } else {
+        Some(s)
+    }
+}
+
+fn get_docs(attrs: &[Attribute]) -> Option<String> {
+    let doc_attrs = attrs
+        .iter()
+        .filter_map(|attr| {
+            if !attr.path.is_ident("doc") {
+                return None;
+            }
+
+            let meta = attr.parse_meta().ok()?;
+            if let NameValue(MetaNameValue { lit: Str(s), .. }) = meta {
+                return Some(s.value());
+            }
+
+            None
+        })
+        .collect::<Vec<_>>();
+
+    if doc_attrs.is_empty() {
+        return None;
+    }
+
+    let mut docs = doc_attrs
+        .iter()
+        .flat_map(|a| a.split('\n'))
+        .map(str::trim)
+        .skip_while(|s| *s == "")
+        .collect::<Vec<_>>()
+        .join("\n");
+
+    docs.truncate(docs.trim_end().len());
+    Some(docs)
+}