Allow unquoted expressions in default = ...

For backwards compatibility, strings are still interpreted as code inside a string.

Fixes #330

Author: TedDriggs

derive_builder/tests/custom_default.rs

@@ -8,17 +8,17 @@ mod field_level {
         required: String,
         #[builder(default)]
         explicit_default: String,
-        #[builder(default = "\"foo\".to_string()")]
+        #[builder(default = "foo".to_string())]
         escaped_default: String,
-        #[builder(default = r#"format!("Hello {}!", "World")"#)]
+        #[builder(default = format!("Hello {}!", "World"))]
         raw_default: String,
-        #[builder(default = r#"format!("{}-{}-{}-{}",
+        #[builder(default = {format!("{}-{}-{}-{}",
                              Clone::clone(self.required
                                 .as_ref()
                                 .ok_or_else(|| UninitializedFieldError::new("required"))?),
                              match self.explicit_default { Some(ref x) => x, None => "EMPTY" },
                              self.escaped_default.as_ref().map(|x| x.as_ref()).unwrap_or("EMPTY"),
-                             if let Some(ref x) = self.raw_default { x } else { "EMPTY" })"#)]
+                             if let Some(ref x) = self.raw_default { x } else { "EMPTY" })})]
         computed_default: String,
     }
 
@@ -72,9 +72,9 @@ mod field_level {
 
 mod struct_level {
     #[derive(Debug, Clone, PartialEq, Eq, Builder)]
-    #[builder(default = "explicit_default()")]
+    #[builder(default = explicit_default())]
     struct Lorem {
-        #[builder(default = "true")]
+        #[builder(default = true)]
         overwritten: bool,
         not_type_default: Option<&'static str>,
     }

derive_builder/tests/validation.rs

@@ -8,7 +8,7 @@ pub struct Lorem {
     my_effort: u8,
 
     /// A percentile. Must be less than or equal to `Lorem::my_effort`.
-    #[builder(default = "40")]
+    #[builder(default = 40)]
     their_effort: u8,
 
     /// A percentile. Must be between 0 and 100.

derive_builder_core/src/default_expression.rs

@@ -41,6 +41,16 @@ impl darling::FromMeta for DefaultExpression {
         Ok(DefaultExpression::Trait)
     }
 
+    fn from_expr(expr: &syn::Expr) -> darling::Result<Self> {
+        if let syn::Expr::Lit(el) = expr {
+            if let syn::Lit::Str(_) = el.lit {
+                return Self::from_value(&el.lit);
+            }
+        }
+
+        Ok(Self::Explicit(expr.clone().into()))
+    }
+
     fn from_value(value: &syn::Lit) -> darling::Result<Self> {
         Ok(Self::Explicit(BlockContents::from_value(value)?))
     }