Accept field(ty = "...") to ease migration to syn 2.0

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
+- Accept `field(ty = "...")` as an alias for `field(type = "...")` in preparation for moving to syn 2.0, which doesn't allow the use of keywords as meta item paths.
+
 ## [0.13.0] - 2024-01-22
 - Bump MSRV to 1.56.0
 - Add `build_fn(error(validation_error = <bool>))` to disable generation of `ValidationError` within the builder's error so that `alloc::string` is avoided.

derive_builder/src/lib.rs

@@ -645,13 +645,13 @@
 //! #[derive(Debug, PartialEq, Default, Builder, Clone)]
 //! #[builder(derive(Debug, PartialEq))]
 //! struct Lorem {
-//!     #[builder(setter(into), field(type = "u32"))]
+//!     #[builder(setter(into), field(ty = "u32"))]
 //!     ipsum: u32,
 //!
-//!     #[builder(field(type = "String", build = "()"))]
+//!     #[builder(field(ty = "String", build = "()"))]
 //!     dolor: (),
 //!
-//!     #[builder(field(type = "&'static str", build = "self.amet.parse()?"))]
+//!     #[builder(field(ty = "&'static str", build = "self.amet.parse()?"))]
 //!     amet: u32,
 //! }
 //!
@@ -670,7 +670,7 @@
 //! # }
 //! ```
 //!
-//! The builder field type (`type =`) must implement `Default`.
+//! The builder field type (`ty =`) must implement `Default`.
 //!
 //! The argument to `build` must be a literal string containing Rust code for the contents of a block, which must evaluate to the type of the target field.
 //! It may refer to the builder struct as `self`, use `?`, etc.

derive_builder/tests/builder_field_custom.rs

@@ -7,10 +7,10 @@ use std::num::ParseIntError;
 
 #[derive(Debug, PartialEq, Default, Builder, Clone)]
 pub struct Lorem {
-    #[builder(field(type = "Option<usize>", build = "self.ipsum.unwrap_or(42) + 1"))]
+    #[builder(field(ty = "Option<usize>", build = "self.ipsum.unwrap_or(42) + 1"))]
     ipsum: usize,
 
-    #[builder(setter(into), field(type = "String", build = "self.dolor.parse()?"))]
+    #[builder(setter(into), field(ty = "String", build = "self.dolor.parse()?"))]
     dolor: u32,
 }
 

derive_builder/tests/compile-fail/builder_field_custom.rs

@@ -10,12 +10,17 @@ pub struct Lorem {
     )]
     ipsum: usize,
 
-    // `default` is incompatible with `field.type`, even without `field.build`
-    #[builder(default = "2", field(type = "usize"))]
+    // Both `ty` and `type` are temporarily allowed to ease the transition
+    // to syn 2.0, but they are mutually exclusive.
+    #[builder(field(ty = "usize", type = "usize"))]
+    dolor: usize,
+
+    // `default` is incompatible with `field.ty`, even without `field.build`
+    #[builder(default = "2", field(ty = "usize"))]
     sit: usize,
 
     // Both errors can occur on the same field
-    #[builder(default = "3", field(type = "usize", build = "self.ipsum + 42"))]
+    #[builder(default = "3", field(ty = "usize", build = "self.ipsum + 42"))]
     amet: usize,
 }
 

derive_builder/tests/compile-fail/builder_field_custom.stderr

@@ -4,20 +4,26 @@ error: #[builder(default)] and #[builder(field(build="..."))] cannot be used tog
 8 |         default = "1",
   |                   ^^^
 
+error: duplicate field - `type` is a deprecated alias for `ty`.
+  --> tests/compile-fail/builder_field_custom.rs:15:35
+   |
+15 |     #[builder(field(ty = "usize", type = "usize"))]
+   |                                   ^^^^
+
 error: #[builder(default)] and #[builder(field(type="..."))] cannot be used together
-  --> tests/compile-fail/builder_field_custom.rs:14:25
+  --> tests/compile-fail/builder_field_custom.rs:19:25
    |
-14 |     #[builder(default = "2", field(type = "usize"))]
+19 |     #[builder(default = "2", field(ty = "usize"))]
    |                         ^^^
 
 error: #[builder(default)] and #[builder(field(build="..."))] cannot be used together
-  --> tests/compile-fail/builder_field_custom.rs:18:25
+  --> tests/compile-fail/builder_field_custom.rs:23:25
    |
-18 |     #[builder(default = "3", field(type = "usize", build = "self.ipsum + 42"))]
+23 |     #[builder(default = "3", field(ty = "usize", build = "self.ipsum + 42"))]
    |                         ^^^
 
 error: #[builder(default)] and #[builder(field(type="..."))] cannot be used together
-  --> tests/compile-fail/builder_field_custom.rs:18:25
+  --> tests/compile-fail/builder_field_custom.rs:23:25
    |
-18 |     #[builder(default = "3", field(type = "usize", build = "self.ipsum + 42"))]
+23 |     #[builder(default = "3", field(ty = "usize", build = "self.ipsum + 42"))]
    |                         ^^^

derive_builder_core/src/macro_options/darling_opts.rs

@@ -215,23 +215,51 @@ impl Visibility for StructLevelFieldMeta {
     }
 }
 
+fn preserve_field_span(meta: &Meta) -> darling::Result<(Span, syn::Type)> {
+    match meta {
+        Meta::Path(_) => Err(Error::unsupported_format("word").with_span(meta)),
+        Meta::List(_) => Err(Error::unsupported_format("list").with_span(meta)),
+        Meta::NameValue(mnv) => Ok((mnv.path.span(), syn::Type::from_value(&mnv.lit)?)),
+    }
+}
+
 /// Contents of the `field` meta in `builder` attributes at the field level.
 //
 // This is a superset of the attributes permitted in `field` at the struct level.
 // Perhaps in the future we will be able to use `#[darling(flatten)]`, but
 // that does not exist right now: https://github.com/TedDriggs/darling/issues/146
 #[derive(Debug, Clone, Default, FromMeta)]
+#[darling(and_then = "Self::finalize")]
 pub struct FieldLevelFieldMeta {
     public: Flag,
     private: Flag,
     vis: Option<syn::Visibility>,
+    #[darling(rename = "type", with = "preserve_field_span", map = "Some", default)]
+    builder_type_old: Option<(Span, syn::Type)>,
     /// Custom builder field type
-    #[darling(rename = "type")]
+    #[darling(rename = "ty")]
     builder_type: Option<syn::Type>,
     /// Custom builder field method, for making target struct field value
     build: Option<BlockContents>,
 }
 
+impl FieldLevelFieldMeta {
+    fn finalize(mut self) -> darling::Result<Self> {
+        if let Some((type_field_span, ty)) = self.builder_type_old.take() {
+            if self.builder_type.is_some() {
+                return Err(Error::custom(
+                    "duplicate field - `type` is a deprecated alias for `ty`.",
+                )
+                .with_span(&type_field_span));
+            }
+
+            self.builder_type = Some(ty);
+        }
+
+        Ok(self)
+    }
+}
+
 impl Visibility for FieldLevelFieldMeta {
     fn public(&self) -> &Flag {
         &self.public