Add with attribute for field transformations in valuable derive macro

tests/tests/ui/not_valuable.stderr

@@ -1,86 +1,73 @@
-error[E0277]: the trait bound `S: Valuable` is not satisfied
- --> tests/ui/not_valuable.rs:7:8
+error[E0599]: the method `as_value` exists for enum `Option<S>`, but its trait bounds were not satisfied
+ --> tests/ui/not_valuable.rs:5:10
   |
+3 | struct S;
+  | -------- doesn't satisfy `S: Valuable`
+4 |
 5 | #[derive(Valuable)]
-  |          -------- required by a bound introduced by this call
-6 | struct Struct {
-7 |     f: Option<S>,
-  |        ^^^^^^^^^ the trait `Valuable` is not implemented for `S`
+  |          ^^^^^^^^ method cannot be called on `Option<S>` due to unsatisfied trait bounds
   |
-  = help: the following other types implement trait `Valuable`:
-            &T
-            &[T]
-            &mut T
-            &std::path::Path
-            &str
-            ()
-            (T0, T1)
-            (T0, T1, T2)
-          and $N others
-  = note: required for `Option<S>` to implement `Valuable`
+ ::: $RUST/core/src/option.rs
+  |
+  | pub enum Option<T> {
+  | ------------------ doesn't satisfy `Option<S>: Valuable`
+  |
+  = note: the following trait bounds were not satisfied:
+          `S: Valuable`
+          which is required by `Option<S>: Valuable`
+note: the trait `Valuable` must be implemented
+ --> $WORKSPACE/valuable/src/valuable.rs
+  |
+  | pub trait Valuable {
+  | ^^^^^^^^^^^^^^^^^^
+  = note: this error originates in the derive macro `Valuable` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `S: Valuable` is not satisfied
-  --> tests/ui/not_valuable.rs:11:14
+error[E0599]: the method `as_value` exists for enum `Option<S>`, but its trait bounds were not satisfied
+  --> tests/ui/not_valuable.rs:10:10
    |
+3  | struct S;
+   | -------- doesn't satisfy `S: Valuable`
+...
 10 | #[derive(Valuable)]
-   |          -------- required by a bound introduced by this call
-11 | struct Tuple(Option<S>);
-   |              ^^^^^^^^^ the trait `Valuable` is not implemented for `S`
+   |          ^^^^^^^^ method cannot be called on `Option<S>` due to unsatisfied trait bounds
    |
-   = help: the following other types implement trait `Valuable`:
-             &T
-             &[T]
-             &mut T
-             &std::path::Path
-             &str
-             ()
-             (T0, T1)
-             (T0, T1, T2)
-           and $N others
-   = note: required for `Option<S>` to implement `Valuable`
-
-error[E0277]: the trait bound `S: Valuable` is not satisfied
-  --> tests/ui/not_valuable.rs:15:25
+  ::: $RUST/core/src/option.rs
    |
-13 | #[derive(Valuable)]
-   |          -------- required by a bound introduced by this call
-14 | enum Enum {
-15 |     Struct { f: Option<S> },
-   |                         ^ the trait `Valuable` is not implemented for `S`
+   | pub enum Option<T> {
+   | ------------------ doesn't satisfy `Option<S>: Valuable`
    |
-   = help: the following other types implement trait `Valuable`:
-             &T
-             &[T]
-             &mut T
-             &std::path::Path
-             &str
-             ()
-             (T0, T1)
-             (T0, T1, T2)
-           and $N others
-   = note: required for `Option<S>` to implement `Valuable`
-   = note: 1 redundant requirement hidden
-   = note: required for `&Option<S>` to implement `Valuable`
+   = note: the following trait bounds were not satisfied:
+           `S: Valuable`
+           which is required by `Option<S>: Valuable`
+note: the trait `Valuable` must be implemented
+  --> $WORKSPACE/valuable/src/valuable.rs
+   |
+   | pub trait Valuable {
+   | ^^^^^^^^^^^^^^^^^^
+   = note: this error originates in the derive macro `Valuable` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `S: Valuable` is not satisfied
-  --> tests/ui/not_valuable.rs:16:19
+error[E0599]: the method `as_value` exists for reference `&Option<S>`, but its trait bounds were not satisfied
+  --> tests/ui/not_valuable.rs:13:10
    |
-13 | #[derive(Valuable)]
-   |          -------- required by a bound introduced by this call
+3  | struct S;
+   | -------- doesn't satisfy `S: Valuable`
 ...
-16 |     Tuple(Option<S>),
-   |                   ^ the trait `Valuable` is not implemented for `S`
+13 | #[derive(Valuable)]
+   |          ^^^^^^^^ method cannot be called on `&Option<S>` due to unsatisfied trait bounds
+   |
+  ::: $RUST/core/src/option.rs
+   |
+   | pub enum Option<T> {
+   | ------------------ doesn't satisfy `Option<S>: Valuable`
+   |
+   = note: the following trait bounds were not satisfied:
+           `S: Valuable`
+           which is required by `Option<S>: Valuable`
+           `Option<S>: Valuable`
+           which is required by `&Option<S>: Valuable`
+note: the trait `Valuable` must be implemented
+  --> $WORKSPACE/valuable/src/valuable.rs
    |
-   = help: the following other types implement trait `Valuable`:
-             &T
-             &[T]
-             &mut T
-             &std::path::Path
-             &str
-             ()
-             (T0, T1)
-             (T0, T1, T2)
-           and $N others
-   = note: required for `Option<S>` to implement `Valuable`
-   = note: 1 redundant requirement hidden
-   = note: required for `&Option<S>` to implement `Valuable`
+   | pub trait Valuable {
+   | ^^^^^^^^^^^^^^^^^^
+   = note: this error originates in the derive macro `Valuable` (in Nightly builds, run with -Z macro-backtrace for more info)

valuable-derive/examples/comprehensive_demo.rs

@@ -0,0 +1,79 @@
+use valuable::Valuable;
+
+/// Stack copy: bool -> bool
+fn invert_flag(active: &bool) -> bool {
+    !*active
+}
+
+/// Heap allocation: u64 -> String
+fn format_id(id: &u64) -> String {
+    format!("ID-{:06}", id)
+}
+
+/// Complex transformation: Vec<String> -> Box<[String]>
+fn uppercase_list(items: &[String]) -> Box<[String]> {
+    items
+        .iter()
+        .map(|s| s.to_uppercase())
+        .collect::<Vec<_>>()
+        .into_boxed_slice()
+}
+
+#[derive(Valuable, Debug)]
+struct Example {
+    id: u64,
+
+    #[valuable(with = "invert_flag")]
+    active: bool,
+
+    #[valuable(with = "format_id")]
+    user_id: u64,
+
+    #[valuable(with = "uppercase_list")]
+    tags: Vec<String>,
+
+    #[valuable(skip)]
+    #[allow(dead_code)]
+    secret: String,
+}
+
+fn main() {
+    let example = Example {
+        id: 42,
+        active: false,
+        user_id: 12345,
+        tags: vec!["admin".to_string(), "user".to_string()],
+        secret: "hidden".to_string(),
+    };
+
+    println!("Debug: {example:?}");
+
+    struct TestVisitor {
+        fields: Vec<(String, String)>,
+    }
+
+    impl valuable::Visit for TestVisitor {
+        fn visit_value(&mut self, _value: valuable::Value<'_>) {}
+
+        fn visit_named_fields(&mut self, named_values: &valuable::NamedValues<'_>) {
+            for (field, value) in named_values {
+                self.fields
+                    .push((field.name().to_string(), format!("{value:?}")));
+            }
+        }
+
+        fn visit_unnamed_fields(&mut self, values: &[valuable::Value<'_>]) {
+            for (i, value) in values.iter().enumerate() {
+                self.fields.push((i.to_string(), format!("{value:?}")));
+            }
+        }
+    }
+
+    let mut visitor = TestVisitor { fields: Vec::new() };
+    example.visit(&mut visitor);
+
+    println!("Valuable fields:");
+    for (name, value) in visitor.fields {
+        println!("  {}: {}", name, value);
+    }
+}

valuable-derive/src/attr.rs

@@ -33,7 +33,7 @@ static ATTRS: &[AttrDef] = &[
     // #[valuable(skip)]
     AttrDef {
         name: "skip",
-        conflicts_with: &["rename"],
+        conflicts_with: &["rename", "with"],
         position: &[
             // TODO: How do we implement Enumerable::variant and Valuable::as_value if a variant is skipped?
             // Position::Variant,
@@ -42,12 +42,20 @@ static ATTRS: &[AttrDef] = &[
         ],
         style: &[MetaStyle::Ident],
     },
+    // #[valuable(with = "...")]
+    AttrDef {
+        name: "with",
+        conflicts_with: &["skip"],
+        position: &[Position::NamedField, Position::UnnamedField],
+        style: &[MetaStyle::NameValue],
+    },
 ];
 
 pub(crate) struct Attrs {
     rename: Option<(syn::MetaNameValue, syn::LitStr)>,
     transparent: Option<Span>,
     skip: Option<Span>,
+    with: Option<(syn::MetaNameValue, syn::LitStr)>,
 }
 
 impl Attrs {
@@ -65,12 +73,20 @@ impl Attrs {
     pub(crate) fn skip(&self) -> bool {
         self.skip.is_some()
     }
+
+    pub(crate) fn with(&self) -> Option<syn::Expr> {
+        self.with.as_ref().map(|(_, lit_str)| {
+            let path_str = lit_str.value();
+            syn::parse_str(&path_str).expect("failed to parse with function path")
+        })
+    }
 }
 
 pub(crate) fn parse_attrs(cx: &Context, attrs: &[syn::Attribute], pos: Position) -> Attrs {
     let mut rename = None;
     let mut transparent = None;
     let mut skip = None;
+    let mut with = None;
 
     let attrs = filter_attrs(cx, attrs, pos);
     for (def, meta) in &attrs {
@@ -104,6 +120,8 @@ pub(crate) fn parse_attrs(cx: &Context, attrs: &[syn::Attribute], pos: Position)
             "transparent" => transparent = Some(meta.span()),
             // #[valuable(skip)]
             "skip" => skip = Some(meta.span()),
+            // #[valuable(with = "...")]
+            "with" => lit_str!(with),
 
             _ => unreachable!("{}", def.name),
         }
@@ -113,6 +131,7 @@ pub(crate) fn parse_attrs(cx: &Context, attrs: &[syn::Attribute], pos: Position)
         rename,
         transparent,
         skip,
+        with,
     }
 }