Add suppress_derive_clone struct attribute

This attribute suppresses the default-generated `derive(Clone)`. This
may be necessary where `derive(Clone)` copies constraints in an
unsatisfiable way.

See: https://smallcultfollowing.com/babysteps//blog/2022/04/12/implied-bounds-and-perfect-derive/
See: rust-lang/rust#26925
Fixes: #325

derive_builder/src/lib.rs

@@ -504,6 +504,11 @@
 //! }
 //! ```
 //!
+//! The `Builder` will also automatically `derive(Clone)` in some cases. This may not always be
+//! suitable if there are generic types involved. This may be suppressed using the
+//! `suppress_derive_clone` attribute. The generated code may still need an `impl Clone for
+//! Builder`; when using this attribute, it will need to be implemented in another way.
+//!
 //! Attributes declared for those traits are _not_ forwarded to the fields on the builder.
 //!
 //! ## Documentation Comments and Attributes

derive_builder/tests/compile-fail/suppress_derive_clone.rs

@@ -0,0 +1,12 @@
+#[macro_use]
+extern crate derive_builder;
+
+#[derive(Builder)]
+#[builder(suppress_derive_clone)]
+pub struct Example {
+    field: String,
+}
+
+fn main() {
+    let _ = LoremBuilder::default().clone();
+}

derive_builder/tests/manual_clone.rs

@@ -0,0 +1,40 @@
+#[macro_use]
+extern crate derive_builder;
+
+#[derive(Debug, Builder, PartialEq, Clone)]
+#[builder(suppress_derive_clone)]
+struct Lorem {
+    #[builder(setter(into))]
+    ipsum: String,
+}
+
+impl Clone for LoremBuilder {
+    fn clone(&self) -> Self {
+        Self {
+            ipsum: self.ipsum.clone(),
+        }
+    }
+}
+
+#[test]
+fn error_if_uninitialized() {
+    let error = LoremBuilder::default().build().unwrap_err();
+    assert_eq!(&error.to_string(), "`ipsum` must be initialized");
+}
+
+#[test]
+fn builder_test() {
+    let x = LoremBuilder::default().ipsum("ipsum").build().unwrap();
+
+    assert_eq!(
+        x,
+        Lorem {
+            ipsum: "ipsum".into()
+        }
+    );
+}
+
+#[test]
+fn builder_is_clone() {
+    let _ = LoremBuilder::default().clone();
+}

derive_builder_core/src/macro_options/darling_opts.rs

@@ -590,6 +590,11 @@ pub struct Options {
 
     #[darling(skip, default)]
     deprecation_notes: DeprecationNotes,
+
+    /// Suppress the `derive(Clone)` attribute.
+    ///
+    /// If `Clone` is needed, it must be generated in some other way.
+    suppress_derive_clone: Flag,
 }
 
 /// Accessors for parsed properties.
@@ -687,7 +692,7 @@ impl Options {
                 .map(|e| *e.validation_error)
                 .unwrap_or(true),
             no_alloc: cfg!(not(any(feature = "alloc", feature = "lib_has_std"))),
-            must_derive_clone: self.requires_clone(),
+            must_derive_clone: self.requires_clone() && !self.suppress_derive_clone.is_present(),
             doc_comment: None,
             deprecation_notes: Default::default(),
             std: !self.no_std.is_present(),