Remove incorrect detection of simple fmt cases

This was intended to detect the simple cases "{var}" and "{var:?}" and emit them
as straightforward Display::fmt and Debug::fmt method calls rather than a write
macro, but this was only to keep the generated code simple and is not important.
It was broken by the changes to how we parse the fmt attr in 1.0.7.

Fixes #53.

impl/src/attr.rs

@@ -20,7 +20,6 @@ pub struct Display<'a> {
     pub original: &'a Attribute,
     pub fmt: LitStr,
     pub args: TokenStream,
-    pub was_shorthand: bool,
     pub has_bonus_display: bool,
 }
 
@@ -82,7 +81,6 @@ fn parse_error_attribute<'a>(attrs: &mut Attrs<'a>, attr: &'a Attribute) -> Resu
             original: attr,
             fmt: input.parse()?,
             args: parse_token_expr(input, false)?,
-            was_shorthand: false,
             has_bonus_display: false,
         };
         if attrs.display.is_some() {
@@ -153,20 +151,8 @@ impl ToTokens for Display<'_> {
     fn to_tokens(&self, tokens: &mut TokenStream) {
         let fmt = &self.fmt;
         let args = &self.args;
-        if self.was_shorthand && fmt.value() == "{}" {
+        tokens.extend(quote! {
-            let arg = args.clone().into_iter().nth(1).unwrap();
+            write!(__formatter, #fmt #args)
-            tokens.extend(quote! {
+        });
-                std::fmt::Display::fmt(#arg, __formatter)
-            });
-        } else if self.was_shorthand && fmt.value() == "{:?}" {
-            let arg = args.clone().into_iter().nth(1).unwrap();
-            tokens.extend(quote! {
-                std::fmt::Debug::fmt(#arg, __formatter)
-            });
-        } else {
-            tokens.extend(quote! {
-                write!(__formatter, #fmt #args)
-            });
-        }
     }
 }

impl/src/fmt.rs

@@ -88,7 +88,6 @@ impl Display<'_> {
         out += read;
         self.fmt = LitStr::new(&out, self.fmt.span());
         self.args = args;
-        self.was_shorthand = true;
         self.has_bonus_display = has_bonus_display;
     }
 }

tests/test_display.rs

@@ -165,3 +165,17 @@ fn test_trailing_comma() {
 
     assert("error ?", Error('?'));
 }
+
+#[test]
+fn test_field() {
+    #[derive(Debug)]
+    struct Inner {
+        data: usize,
+    }
+
+    #[derive(Error, Debug)]
+    #[error("{}", .0.data)]
+    struct Error(Inner);
+
+    assert("0", Error(Inner { data: 0 }));
+}