More attribute refactoring

strum/src/lib.rs

@@ -201,7 +201,7 @@ macro_rules! DocumentMacroRexports {
 // for docsrs. You can do a weird thing where you rename the macro
 // and then reference it through strum. The renaming feature should be deprecated now that
 // 2018 edition is almost 2 years old, but we'll need to give people some time to do that.
-DocumentMacroRexports!{
+DocumentMacroRexports! {
     AsRefStr,
     AsStaticStr,
     Display,

strum_macros/src/helpers/case_style.rs

@@ -1,5 +1,9 @@
 use heck::{CamelCase, KebabCase, MixedCase, ShoutySnakeCase, SnakeCase, TitleCase};
-use syn::Ident;
+use std::str::FromStr;
+use syn::{
+    parse::{Parse, ParseStream},
+    Ident, LitStr,
+};
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub enum CaseStyle {
@@ -15,9 +19,41 @@ pub enum CaseStyle {
     PascalCase,
 }
 
-impl<'s> From<&'s str> for CaseStyle {
-    fn from(text: &'s str) -> CaseStyle {
-        match text {
+const VALID_CASE_STYLES: &[&str] = &[
+    "camelCase",
+    "PascalCase",
+    "kebab-case",
+    "snake_case",
+    "SCREAMING_SNAKE_CASE",
+    "SCREAMING-KEBAB-CASE",
+    "lowercase",
+    "UPPERCASE",
+    "title_case",
+    "mixed_case",
+];
+
+impl Parse for CaseStyle {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let text = input.parse::<LitStr>()?;
+        let val = text.value();
+
+        val.as_str().parse().map_err(|_| {
+            syn::Error::new_spanned(
+                &text,
+                format!(
+                    "Unexpected case style for serialize_all: `{}`. Valid values are: `{:?}`",
+                    val, VALID_CASE_STYLES
+                ),
+            )
+        })
+    }
+}
+
+impl FromStr for CaseStyle {
+    type Err = ();
+
+    fn from_str(text: &str) -> Result<CaseStyle, ()> {
+        Ok(match text {
             "camel_case" | "PascalCase" => CaseStyle::PascalCase,
             "camelCase" => CaseStyle::CamelCase,
             "snake_case" | "snek_case" => CaseStyle::SnakeCase,
@@ -30,23 +66,8 @@ impl<'s> From<&'s str> for CaseStyle {
             "mixed_case" => CaseStyle::MixedCase,
             "lowercase" => CaseStyle::LowerCase,
             "UPPERCASE" => CaseStyle::UpperCase,
-            _ => panic!(
-                "Unexpected case style for serialize_all: `{}`. Valid values are: `{:?}`",
-                text,
-                [
-                    "camelCase",
-                    "PascalCase",
-                    "kebab-case",
-                    "snake_case",
-                    "SCREAMING_SNAKE_CASE",
-                    "SCREAMING-KEBAB-CASE",
-                    "lowercase",
-                    "UPPERCASE",
-                    "title_case",
-                    "mixed_case",
-                ]
-            ),
-        }
+            _ => return Err(()),
+        })
     }
 }