Support for custom default fuction with owned pattern

derive_builder/CHANGELOG.md

@@ -2,6 +2,9 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [Unreleased]
+- Allow default values that access `self` in combination with the "owned" pattern. #298
+
 ## [0.20.0] - 2024-02-14
 - Bump `syn` to version 2 #308
 - Bump `darling` to version 0.20.6 #308

derive_builder/tests/compile-fail/crate_root.stderr

@@ -24,24 +24,6 @@ help: consider importing one of these items
 5 | use std::option::Option;
   |
 
-error[E0433]: failed to resolve: could not find `export` in `empty`
- --> tests/compile-fail/crate_root.rs:7:10
-  |
-7 | #[derive(Builder)]
-  |          ^^^^^^^ not found in `empty::export::core::clone`
-  |
-  = note: this error originates in the derive macro `Builder` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: consider importing one of these items
-  |
-5 | use core::clone::Clone;
-  |
-5 | use derive_builder::export::core::clone::Clone;
-  |
-5 | use serde::__private::Clone;
-  |
-5 | use std::clone::Clone;
-  |
-
 error[E0433]: failed to resolve: could not find `export` in `empty`
  --> tests/compile-fail/crate_root.rs:7:10
   |
@@ -91,6 +73,24 @@ help: consider importing this struct
 5 | use derive_builder::UninitializedFieldError;
   |
 
+error[E0433]: failed to resolve: could not find `export` in `empty`
+ --> tests/compile-fail/crate_root.rs:7:10
+  |
+7 | #[derive(Builder)]
+  |          ^^^^^^^ not found in `empty::export::core::clone`
+  |
+  = note: this error originates in the derive macro `Builder` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider importing one of these items
+  |
+5 | use core::clone::Clone;
+  |
+5 | use derive_builder::export::core::clone::Clone;
+  |
+5 | use serde::__private::Clone;
+  |
+5 | use std::clone::Clone;
+  |
+
 error[E0433]: failed to resolve: could not find `export` in `empty`
  --> tests/compile-fail/crate_root.rs:7:10
   |

derive_builder/tests/custom_default.rs

@@ -136,3 +136,53 @@ mod struct_level {
         assert_eq!(ipsum.not_type_default, None);
     }
 }
+
+mod owned_field {
+
+    #[derive(Debug, Clone, PartialEq, Eq, Builder)]
+    #[builder(pattern = "owned")]
+    struct Lorem {
+        #[builder(default = "self.ipsum_default()")]
+        ipsum: String,
+
+        #[builder(setter(skip), default = "self.dolor_default()")]
+        dolor: String,
+    }
+
+    impl LoremBuilder {
+        fn ipsum_default(&self) -> String {
+            "ipsum".to_string()
+        }
+        fn dolor_default(&self) -> String {
+            "dolor".to_string()
+        }
+    }
+
+    #[test]
+    fn builder_test() {
+        let x = LoremBuilder::create_empty()
+            .ipsum("Ipsum".to_string())
+            .build()
+            .unwrap();
+
+        assert_eq!(
+            x,
+            Lorem {
+                ipsum: "Ipsum".to_string(),
+                dolor: "dolor".to_string(),
+            }
+        );
+    }
+    #[test]
+    fn defaults_test() {
+        let x = LoremBuilder::create_empty().build().unwrap();
+
+        assert_eq!(
+            x,
+            Lorem {
+                ipsum: "ipsum".to_string(),
+                dolor: "dolor".to_string(),
+            }
+        );
+    }
+}

derive_builder_core/src/build_method.rs

@@ -5,7 +5,8 @@ use quote::{ToTokens, TokenStreamExt};
 use syn::spanned::Spanned;
 
 use crate::{
-    doc_comment_from, BuilderPattern, DefaultExpression, Initializer, DEFAULT_STRUCT_NAME,
+    doc_comment_from, BuilderPattern, DefaultExpression, FieldDefaultValue, Initializer,
+    DEFAULT_STRUCT_NAME,
 };
 
 /// Initializer for the struct fields in the build method, implementing
@@ -57,6 +58,8 @@ pub struct BuildMethod<'a> {
     pub error_ty: syn::Path,
     /// Field initializers for the target type.
     pub initializers: Vec<TokenStream>,
+    /// Default values for the target type
+    pub defaults: Vec<TokenStream>,
     /// Doc-comment of the builder struct.
     pub doc_comment: Option<syn::Attribute>,
     /// Default value for the whole struct.
@@ -74,6 +77,7 @@ impl<'a> ToTokens for BuildMethod<'a> {
         let vis = &self.visibility;
         let target_ty = &self.target_ty;
         let target_ty_generics = &self.target_ty_generics;
+        let defaults = &self.defaults;
         let initializers = &self.initializers;
         let self_param = match self.pattern {
             BuilderPattern::Owned => quote!(self),
@@ -100,6 +104,7 @@ impl<'a> ToTokens for BuildMethod<'a> {
                 {
                     #validate_fn
                     #default_struct
+                    #(#defaults)*
                     Ok(#target_ty {
                         #(#initializers)*
                     })
@@ -125,6 +130,16 @@ impl<'a> BuildMethod<'a> {
         self.initializers.push(quote!(#init));
         self
     }
+
+    /// Populate the `BuildMethod` with appropiate default values of
+    /// the underlying struct.
+    ///
+    /// For each struct field this must be called with the appropriate
+    /// default value.
+    pub fn push_default(&mut self, default: FieldDefaultValue) -> &mut Self {
+        self.defaults.push(quote!(#default));
+        self
+    }
 }
 
 // pub struct BuildMethodError {
@@ -150,6 +165,7 @@ macro_rules! default_build_method {
             target_ty_generics: None,
             error_ty: syn::parse_quote!(FooBuilderError),
             initializers: vec![quote!(foo: self.foo,)],
+            defaults: vec![quote!()],
             doc_comment: None,
             default_struct: None,
             validate_fn: None,