Clean up Some Clippy Warnings (#478)

* clippy: it is more idiomatic to loop over references to containers instead of using explicit iteration methods

* clippy: useless use of `format!`

* clippy: if/else is an expression

* clippy: use of  followed by a function call

* clippy: large size difference between variants

* clippy: redundant closure

* Revert "clippy: large size difference between variants"

This reverts commit 7e2e660dd47c9718126d1c45ae1caa632e287a14.

* Revert "clippy: it is more idiomatic to loop over references to containers instead of using explicit iteration methods"

This reverts commit 5c4804f790fc6a33a7a0f0d2aacdc4b98529b978.

crates/backend/src/ast.rs

@@ -217,7 +217,7 @@ impl Function {
 
 impl Export {
     pub(crate) fn rust_symbol(&self) -> Ident {
-        let mut generated_name = format!("__wasm_bindgen_generated");
+        let mut generated_name = String::from("__wasm_bindgen_generated");
         if let Some(class) = &self.class {
             generated_name.push_str("_");
             generated_name.push_str(&class.to_string());

crates/backend/src/codegen.rs

@@ -314,11 +314,12 @@ impl ToTokens for ast::Export {
         let mut converted_arguments = vec![];
         let ret = Ident::new("_ret", Span::call_site());
 
-        let mut offset = 0;
-        if self.method_self.is_some() {
+        let offset = if self.method_self.is_some() {
             args.push(quote! { me: u32 });
-            offset = 1;
-        }
+            1
+        } else {
+            0
+        };
 
         let name = &self.function.name;
         let receiver = match self.method_self {

crates/webidl/src/first_pass.rs

@@ -125,7 +125,7 @@ impl FirstPass for webidl::ast::NonPartialMixin {
         let entry = record
             .mixins
             .entry(self.name.clone())
-            .or_insert(Default::default());
+            .or_insert_with(Default::default);
         if mem::replace(&mut entry.non_partial, Some(self)).is_some() {
             warn!(
                 "Encounterd multiple declarations of {}, using last encountered",
@@ -142,7 +142,7 @@ impl FirstPass for webidl::ast::PartialMixin {
         let entry = record
             .mixins
             .entry(self.name.clone())
-            .or_insert(Default::default());
+            .or_insert_with(Default::default);
         entry.partials.push(self);
 
         Ok(())

crates/webidl/src/util.rs

@@ -247,7 +247,7 @@ impl<'a> FirstPassRecord<'a> {
         let js_ret = ret.clone();
 
         if catch {
-            ret = Some(ret.map_or_else(|| result_ty(unit_ty()), |ret| result_ty(ret)))
+            ret = Some(ret.map_or_else(|| result_ty(unit_ty()), result_ty))
         }
 
         let shim = {