Add #[patch(empty_value=...)] (#134)

Author: yanganto

.github/workflows/test.yml

@@ -62,5 +62,7 @@ jobs:
         run: |
           nix develop .#ci -c cargo run --example status
           nix develop .#ci -c cargo run --example op
+          nix develop .#ci -c cargo run --example clap
           nix develop .#ci -c cargo run --features=nesting --example nesting
+          nix develop .#ci -c cargo run --features=nesting --example clap
           nix develop .#ci -c cargo test

Cargo.toml

@@ -7,7 +7,7 @@ members = [
 
 [workspace.package]
 authors = ["Antonio Yang <yanganto@gmail.com>"]
-version = "0.10.4"
+version = "0.10.5"
 edition = "2021"
 categories = ["development-tools"]
 keywords = ["struct", "patch", "macro", "derive", "overlay"]

README.md

@@ -110,8 +110,9 @@ Field attributes:
 - `#[patch(name = "...")]`: change the type of the field in the generated patch struct.
 - `#[patch(attribute(...))]`: add attributes to the field in the generated patch struct.
 - `#[patch(attribute(derive(...)))]`: add derives to the field in the generated patch struct.
+- `#[patch(empty_value = ...)]`: define a value as empty, so the corresponding field of patch will not wrapped by Option, and apply patch when the field is empty.
 - `#[filler(extendable)]`: use the struct of field for filler, the struct needs implement `Default`, `Extend`, `IntoIterator` and `is_empty`.
-- `#[filler(empty_value)]`: define a value as empty, so the corresponding field of Filler will be applied, even the field is not `Option` or `Extendable`.
+- `#[filler(empty_value = ...)]`: define a value as empty, so the corresponding field of Filler will be applied, even the field is not `Option` or `Extendable`.
 
 Please check the [traits][doc-traits] of document to learn more.
 

derive/src/filler.rs

@@ -1,9 +1,7 @@
 use proc_macro2::{Ident, Span, TokenStream};
 use quote::{quote, ToTokens};
 use std::str::FromStr;
-use syn::meta::ParseNestedMeta;
-use syn::spanned::Spanned;
-use syn::{parenthesized, DeriveInput, Error, Lit, LitStr, Result, Type};
+use syn::{parenthesized, DeriveInput, Lit, LitStr, Result, Type};
 
 #[cfg(feature = "op")]
 use crate::Addable;
@@ -415,7 +413,7 @@ impl Field {
                             return Err(meta
                                 .error("The field is already the field of filler, we can't defined more than once"));
                         }
-                        if let Some(lit) = get_lit(path, &meta)? {
+                        if let Some(lit) = crate::get_lit(path, &meta)? {
                             fty = Some(FillerType::NativeValue(lit));
                         } else {
                             return Err(meta
@@ -429,6 +427,7 @@ impl Field {
                     }
                     #[cfg(not(feature = "op"))]
                     ADDABLE => {
+                        use syn::spanned::Spanned;
                         return Err(syn::Error::new(
                             ident.span(),
                             "`addable` needs `op` feature",
@@ -501,22 +500,3 @@ fn none_option_filler_type(ty: &Type) -> Ident {
         panic!("#[filler(extendable)] should use on a type")
     }
 }
-
-fn get_lit(attr_name: String, meta: &ParseNestedMeta) -> syn::Result<Option<syn::Lit>> {
-    let expr: syn::Expr = meta.value()?.parse()?;
-    let mut value = &expr;
-    while let syn::Expr::Group(e) = value {
-        value = &e.expr;
-    }
-    if let syn::Expr::Lit(syn::ExprLit { lit, .. }) = value {
-        Ok(Some(lit.clone()))
-    } else {
-        Err(Error::new(
-            expr.span(),
-            format!(
-                "expected serde {} attribute to be lit: `{} = \"...\"`",
-                attr_name, attr_name
-            ),
-        ))
-    }
-}

derive/src/lib.rs

@@ -5,6 +5,10 @@ mod patch;
 use filler::Filler;
 use patch::Patch;
 
+use syn::meta::ParseNestedMeta;
+use syn::spanned::Spanned;
+use syn::Error;
+
 #[cfg(feature = "op")]
 pub(crate) enum Addable {
     Disable,
@@ -29,3 +33,23 @@ pub fn derive_filler(item: proc_macro::TokenStream) -> proc_macro::TokenStream {
         .unwrap()
         .into()
 }
+
+fn get_lit(attr_name: String, meta: &ParseNestedMeta) -> syn::Result<Option<syn::Lit>> {
+    let expr: syn::Expr = meta.value()?.parse()?;
+    let mut value = &expr;
+    while let syn::Expr::Group(e) = value {
+        value = &e.expr;
+    }
+    if let syn::Expr::Lit(syn::ExprLit { lit, .. }) = value {
+        Ok(Some(lit.clone()))
+    } else {
+        Err(Error::new(
+            expr.span(),
+            format!(
+                "expected serde {} attribute to be lit: `{} = \"...\"`",
+                attr_name, attr_name
+            ),
+        ))
+    }
+}
+