Add setter(each = "...") option to extend collection-like fields (#199)

Co-authored-by: Andrii Kuteiko <kuteiko@amazon.com>

derive_builder/tests/setter_extend.rs

@@ -0,0 +1,94 @@
+#[macro_use]
+extern crate pretty_assertions;
+#[macro_use]
+extern crate derive_builder;
+
+use std::collections::HashMap;
+
+#[derive(Debug, PartialEq, Default, Builder, Clone)]
+struct Lorem {
+    #[builder(setter(each = "foo_append"))]
+    foo: String,
+    #[builder(setter(each = "bar"))]
+    bars: Vec<String>,
+    #[builder(setter(each = "baz"))]
+    bazes: HashMap<String, i32>,
+}
+
+#[derive(Debug, PartialEq, Default, Builder, Clone)]
+#[builder(pattern = "mutable")]
+struct Ipsum {
+    #[builder(setter(each = "foo_append"))]
+    foo: String,
+    #[builder(setter(each = "bar"))]
+    bars: Vec<String>,
+    #[builder(setter(each = "baz"))]
+    bazes: HashMap<String, i32>,
+}
+
+#[test]
+fn extend_field() {
+    let x = LoremBuilder::default()
+        .foo("foo".into())
+        .bar("bar".into())
+        .bar("bar bar".into())
+        .bar("bar bar bar".into())
+        .foo_append('-')
+        .baz(("baz".into(), 1))
+        .baz(("bazz".into(), 2))
+        .baz(("bazzz".into(), 3))
+        .foo_append("foo")
+        .build()
+        .unwrap();
+
+    assert_eq!(
+        x,
+        Lorem {
+            foo: "foo-foo".into(),
+            bars: vec!["bar".into(), "bar bar".into(), "bar bar bar".into()],
+            bazes: vec![("baz".into(), 1), ("bazz".into(), 2), ("bazzz".into(), 3)]
+                .into_iter()
+                .collect(),
+        }
+    );
+}
+
+#[test]
+fn extend_field_mutable() {
+    let x = IpsumBuilder::default()
+        .foo("foo".into())
+        .bar("bar".into())
+        .bar("bar bar".into())
+        .bar("bar bar bar".into())
+        .foo_append('-')
+        .baz(("baz".into(), 1))
+        .baz(("bazz".into(), 2))
+        .baz(("bazzz".into(), 3))
+        .foo_append("foo")
+        .build()
+        .unwrap();
+
+    assert_eq!(
+        x,
+        Ipsum {
+            foo: "foo-foo".into(),
+            bars: vec!["bar".into(), "bar bar".into(), "bar bar bar".into()],
+            bazes: vec![("baz".into(), 1), ("bazz".into(), 2), ("bazzz".into(), 3)]
+                .into_iter()
+                .collect(),
+        }
+    );
+}
+
+#[derive(Debug, PartialEq, Default, Builder, Clone)]
+#[builder(setter(skip))]
+struct Dolor {
+    #[builder(setter(each = "foo"))]
+    foos: Vec<i32>,
+}
+
+#[test]
+fn extend_field_enabled() {
+    let x = DolorBuilder::default().foo(1).foo(2).build().unwrap();
+    assert_eq!(x, Dolor { foos: vec![1, 2] });
+}

derive_builder_core/src/macro_options/darling_opts.rs

@@ -130,6 +130,7 @@ pub struct FieldLevelSetter {
     strip_option: Option<bool>,
     skip: Option<bool>,
     custom: Option<bool>,
+    each: Option<Ident>,
 }
 
 impl FieldLevelSetter {
@@ -156,6 +157,7 @@ impl FieldLevelSetter {
             || self.name.is_some()
             || self.into.is_some()
             || self.strip_option.is_some()
+            || self.each.is_some()
         {
             return Some(true);
         }
@@ -555,6 +557,7 @@ impl<'a> FieldWithDefaults<'a> {
             generic_into: self.setter_into(),
             strip_option: self.setter_strip_option(),
             deprecation_notes: self.deprecation_notes(),
+            each: self.field.setter.each.as_ref(),
         }
     }
 

derive_builder_core/src/setter.rs

@@ -62,6 +62,8 @@ pub struct Setter<'a> {
     pub strip_option: bool,
     /// Emit deprecation notes to the user.
     pub deprecation_notes: &'a DeprecationNotes,
+    /// Emit extend method.
+    pub each: Option<&'a syn::Ident>,
 }
 
 impl<'a> ToTokens for Setter<'a> {
@@ -135,7 +137,8 @@ impl<'a> ToTokens for Setter<'a> {
                     let mut new = #self_into_return_ty;
                     new.#field_ident = ::derive_builder::export::core::option::Option::Some(#into_value);
                     new
-            }));
+                }
+            ));
 
             if self.try_setter {
                 let try_ty_params =
@@ -151,7 +154,26 @@ impl<'a> ToTokens for Setter<'a> {
                         let mut new = #self_into_return_ty;
                         new.#field_ident = ::derive_builder::export::core::option::Option::Some(converted);
                         Ok(new)
-                }));
+                    }
+                ));
+            }
+
+            if let Some(ref ident_each) = self.each {
+                tokens.append_all(quote!(
+                    #(#attrs)*
+                    #[allow(unused_mut)]
+                    #vis fn #ident_each <VALUE>(#self_param, item: VALUE) -> #return_ty
+                    where
+                        #ty: ::derive_builder::export::core::default::Default + ::derive_builder::export::core::iter::Extend<VALUE>,
+                    {
+                        #deprecation_notes
+                        let mut new = #self_into_return_ty;
+                        new.#field_ident
+                            .get_or_insert_with(::derive_builder::export::core::default::Default::default)
+                            .extend(::derive_builder::export::core::option::Option::Some(item));
+                        new
+                    }
+                ));
             }
         }
     }
@@ -222,6 +244,7 @@ macro_rules! default_setter {
             generic_into: false,
             strip_option: false,
             deprecation_notes: &Default::default(),
+            each: None,
         };
     };
 }