Derive the class_name if missing

derive/Cargo.toml

@@ -12,6 +12,7 @@ proc-macro = true
 quote = "1.0"
 proc-macro2 = "1.0"
 proc-macro-crate = "1.2.1"
+str_inflector = "0.12.0"
 
 [dependencies.syn]
 version = "1.0.101"

derive/src/lib.rs

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use inflector::Inflector;
 use proc_macro::TokenStream;
 use proc_macro2::{Literal, Span};
 use proc_macro_crate::{crate_name, FoundCrate};
@@ -54,13 +55,20 @@ fn get_class_and_element_names(args: Vec<NestedMeta>) -> (Literal, Literal, Lite
             }
         }
     }
+    // TODO(jwall): it should be a compile error if this is missing.
     let class_name = class_name
         .map(|n| n.token())
         .unwrap_or_else(|| LitStr::new("", Span::call_site()).token());
 
-    let element_name = element_name
+    // TODO(jwall): if Missing we should derive this from the class name.
-        .map(|n| n.token())
+    let element_name = match element_name.map(|n| n.token()) {
-        .unwrap_or_else(|| LitStr::new("", Span::call_site()).token());
+        Some(n) => n,
+        None => {
+            let class_kebab = class_name.to_string().to_kebab_case();
+            LitStr::new(&class_kebab, Span::call_site()).token()
+        }
+    };
+
     let observed_attributes = observed_attributes
         .map(|n| n.token())
         .unwrap_or_else(|| LitStr::new("[]", Span::call_site()).token());

web-component/src/lib.rs

@@ -67,59 +67,6 @@ mod tests {
 
     wasm_bindgen_test::wasm_bindgen_test_configure!(run_in_browser);
 
-    #[web_component(
-        class_name = "MyElement",
-        element_name = "my-element",
-        observed_attrs = "['class']"
-    )]
-    pub struct MyElementImpl {}
-
-    impl WebComponentBinding for MyElementImpl {
-        fn connected(&self, element: &HtmlElement) {
-            log("Firing connected call back".to_owned());
-            let node = Text::new().unwrap();
-            node.set_text_content(Some("Added a text node on connect".into()));
-            element.append_child(&node).unwrap();
-            log(format!(
-                "element contents: {}",
-                &element.text_content().unwrap()
-            ));
-        }
-
-        fn disconnected(&self, element: &HtmlElement) {
-            log("Firing discconnected call back".to_owned());
-            let node = element.first_child().unwrap();
-            element.remove_child(&node).unwrap();
-        }
-
-        fn adopted(&self, element: &HtmlElement) {
-            log("Firing adopted call back".to_owned());
-            let node = Text::new().unwrap();
-            node.set_text_content(Some("Added a text node on adopt".into()));
-            element.append_child(&node).unwrap();
-            log_with_val("element: ".to_owned(), element);
-        }
-
-        fn attribute_changed(
-            &self,
-            element: &HtmlElement,
-            name: JsValue,
-            old_value: JsValue,
-            new_value: JsValue,
-        ) {
-            log("Firing attribute changed callback".to_owned());
-            let node = element.first_child().unwrap();
-            node.set_text_content(Some(&format!(
-                "Setting {} from {} to {}",
-                name.as_string().unwrap_or("None".to_owned()),
-                old_value.as_string().unwrap_or("None".to_owned()),
-                new_value.as_string().unwrap_or("None".to_owned()),
-            )));
-            element.append_child(&node).unwrap();
-            log_with_val("element: ".to_owned(), element);
-        }
-    }
-
     #[wasm_bindgen]
     extern "C" {
         #[wasm_bindgen(js_namespace = console, js_name = log)]
@@ -132,6 +79,58 @@ mod tests {
     // to the handle we run this all in one single function.
     #[wasm_bindgen_test]
     fn test_component() {
+        #[web_component(
+            class_name = "MyElement",
+            element_name = "my-element",
+            observed_attrs = "['class']"
+        )]
+        pub struct MyElementImpl {}
+
+        impl WebComponentBinding for MyElementImpl {
+            fn connected(&self, element: &HtmlElement) {
+                log("Firing connected call back".to_owned());
+                let node = Text::new().unwrap();
+                node.set_text_content(Some("Added a text node on connect".into()));
+                element.append_child(&node).unwrap();
+                log(format!(
+                    "element contents: {}",
+                    &element.text_content().unwrap()
+                ));
+            }
+
+            fn disconnected(&self, element: &HtmlElement) {
+                log("Firing discconnected call back".to_owned());
+                let node = element.first_child().unwrap();
+                element.remove_child(&node).unwrap();
+            }
+
+            fn adopted(&self, element: &HtmlElement) {
+                log("Firing adopted call back".to_owned());
+                let node = Text::new().unwrap();
+                node.set_text_content(Some("Added a text node on adopt".into()));
+                element.append_child(&node).unwrap();
+                log_with_val("element: ".to_owned(), element);
+            }
+
+            fn attribute_changed(
+                &self,
+                element: &HtmlElement,
+                name: JsValue,
+                old_value: JsValue,
+                new_value: JsValue,
+            ) {
+                log("Firing attribute changed callback".to_owned());
+                let node = element.first_child().unwrap();
+                node.set_text_content(Some(&format!(
+                    "Setting {} from {} to {}",
+                    name.as_string().unwrap_or("None".to_owned()),
+                    old_value.as_string().unwrap_or("None".to_owned()),
+                    new_value.as_string().unwrap_or("None".to_owned()),
+                )));
+                element.append_child(&node).unwrap();
+                log_with_val("element: ".to_owned(), element);
+            }
+        }
         let obj = MyElementImpl::define().expect("Failed to define web component");
         let fun = obj.element_constructor.dyn_ref::<Function>().unwrap();
         assert_eq!(fun.name(), MyElementImpl::class_name());
@@ -171,4 +170,13 @@ mod tests {
             "Added a text node on adopt"
         );
     }
+
+    #[wasm_bindgen_test]
+    fn test_component_no_element_name() {
+        #[web_component(class_name = "AnElement")]
+        pub struct AnElement {}
+        impl WebComponentBinding for AnElement {}
+
+        assert_eq!(AnElement::element_name(), "an-element");
+    }
 }