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Expanded #[serder(default = ...)] capabilities. #2728

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Expanded #[serder(default = ...)] capabilities. #2728

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a80ce16
added support for default values on fields in addition to a path to a…
Threadzless Apr 13, 2024
3028491
incremented version number
Threadzless Apr 13, 2024
e72dc96
changed `serde_derive`s version requirement to match the new version …
Threadzless Apr 13, 2024
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4 changes: 2 additions & 2 deletions serde/Cargo.toml
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
[package]
name = "serde"
version = "1.0.197"
version = "1.0.198"
authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay@gmail.com>"]
build = "build.rs"
categories = ["encoding", "no-std", "no-std::no-alloc"]
Expand Down Expand Up @@ -37,7 +37,7 @@ rustdoc-args = ["--cfg", "doc_cfg", "--generate-link-to-definition"]
# is compatible with exactly one serde release because the generated code
# involves nonpublic APIs which are not bound by semver.
[target.'cfg(any())'.dependencies]
serde_derive = { version = "=1.0.197", path = "../serde_derive" }
serde_derive = { version = "=1.0.198", path = "../serde_derive" }


### FEATURES #################################################################
Expand Down
2 changes: 1 addition & 1 deletion serde_derive/Cargo.toml
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
[package]
name = "serde_derive"
version = "1.0.197"
version = "1.0.198"
authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay@gmail.com>"]
categories = ["no-std", "no-std::no-alloc"]
description = "Macros 1.1 implementation of #[derive(Serialize, Deserialize)]"
Expand Down
31 changes: 28 additions & 3 deletions serde_derive/src/de.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -174,7 +174,9 @@ fn build_generics(cont: &Container, borrowed: &BorrowedLifetimes) -> syn::Generi
&generics,
&parse_quote!(_serde::__private::Default),
),
attr::Default::None | attr::Default::Path(_) => generics,
attr::Default::None |
attr::Default::Expr(_) |
attr::Default::Path(_) => generics,
};

let delife = borrowed.de_lifetime();
Expand Down Expand Up @@ -373,6 +375,7 @@ fn deserialize_transparent(cont: &Container, params: &Parameters) -> Fragment {
attr::Default::Default => quote!(_serde::__private::Default::default()),
attr::Default::Path(path) => quote!(#path()),
attr::Default::None => quote!(_serde::__private::PhantomData),
attr::Default::Expr(lit) => quote!(#lit),
};
quote!(#member: #value)
}
Expand Down Expand Up @@ -754,6 +757,9 @@ fn deserialize_seq(
attr::Default::Path(path) => Some(quote!(
let __default: Self::Value = #path();
)),
attr::Default::Expr(lit) => Some(quote!(
let __default: Self::Value = #lit;
)),
attr::Default::None => {
// We don't need the default value, to prevent an unused variable warning
// we'll leave the line empty.
Expand Down Expand Up @@ -836,6 +842,9 @@ fn deserialize_seq_in_place(
attr::Default::Path(path) => Some(quote!(
let __default: #this_type #ty_generics = #path();
)),
attr::Default::Expr(lit) => Some(quote!(
let __default: #this_type #ty_generics = #lit;
)),
attr::Default::None => {
// We don't need the default value, to prevent an unused variable warning
// we'll leave the line empty.
Expand Down Expand Up @@ -2637,6 +2646,9 @@ fn deserialize_map(
attr::Default::Path(path) => Some(quote!(
let __default: Self::Value = #path();
)),
attr::Default::Expr(lit) => Some(quote!(
let __default: Self::Value = #lit
)),
attr::Default::None => {
// We don't need the default value, to prevent an unused variable warning
// we'll leave the line empty.
Expand Down Expand Up @@ -2804,6 +2816,9 @@ fn deserialize_map_in_place(
attr::Default::Path(path) => Some(quote!(
let __default: #this_type #ty_generics = #path();
)),
attr::Default::Expr(lit) => Some(quote!(
let __default: #this_type #ty_generics = #lit;
)),
attr::Default::None => {
// We don't need the default value, to prevent an unused variable warning
// we'll leave the line empty.
Expand Down Expand Up @@ -2947,11 +2962,16 @@ fn expr_is_missing(field: &Field, cattrs: &attr::Container) -> Fragment {
attr::Default::Path(path) => {
return quote_expr!(#path());
}
attr::Default::Expr(lit) => {
return quote_expr!(#lit);
}
attr::Default::None => { /* below */ }
}

match *cattrs.default() {
attr::Default::Default | attr::Default::Path(_) => {
attr::Default::Default |
attr::Default::Path(_) |
attr::Default::Expr(_) => {
let member = &field.member;
return quote_expr!(__default.#member);
}
Expand Down Expand Up @@ -2990,11 +3010,16 @@ fn expr_is_missing_seq(
attr::Default::Path(path) => {
return quote_spanned!(path.span()=> #assign_to #path());
}
attr::Default::Expr(lit) => {
return quote_spanned!(lit.span()=> #assign_to #lit);
}
attr::Default::None => { /* below */ }
}

match *cattrs.default() {
attr::Default::Default | attr::Default::Path(_) => {
attr::Default::Default |
attr::Default::Path(_) |
attr::Default::Expr(_) => {
let member = &field.member;
quote!(#assign_to __default.#member)
}
Expand Down
75 changes: 62 additions & 13 deletions serde_derive/src/internals/attr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -396,24 +396,21 @@ impl Container {
deny_unknown_fields.set_true(meta.path);
} else if meta.path == DEFAULT {
if meta.input.peek(Token![=]) {
// #[serde(default = "...")]
if let Some(path) = parse_lit_into_expr_path(cx, DEFAULT, &meta)? {
// #[serde(default = ...)]
if let Some(dflt) = parse_default(cx, &meta)? {
match &item.data {
syn::Data::Struct(syn::DataStruct { fields, .. }) => match fields {
syn::Fields::Named(_) | syn::Fields::Unnamed(_) => {
default.set(&meta.path, Default::Path(path));
default.set(&meta.path, dflt);
}
syn::Fields::Unit => {
let msg = "#[serde(default = \"...\")] can only be used on structs that have fields";
let msg = "#[serde(default = ...)] can only be used on structs that have fields";
cx.syn_error(meta.error(msg));
}
},
syn::Data::Enum(_) => {
let msg = "#[serde(default = \"...\")] can only be used on structs";
cx.syn_error(meta.error(msg));
}
syn::Data::Enum(_) |
syn::Data::Union(_) => {
let msg = "#[serde(default = \"...\")] can only be used on structs";
let msg = "#[serde(default = ...)] can only be used on structs";
cx.syn_error(meta.error(msg));
}
}
Expand Down Expand Up @@ -1055,13 +1052,17 @@ pub enum Default {
Default,
/// The default is given by this function.
Path(syn::ExprPath),
/// The default is a literal value
Expr(Box<syn::Expr>),
}

impl Default {
pub fn is_none(&self) -> bool {
match self {
Default::None => true,
Default::Default | Default::Path(_) => false,
Default::Default |
Default::Path(_) |
Default::Expr(_) => false,
}
}
}
Expand Down Expand Up @@ -1140,9 +1141,9 @@ impl Field {
}
} else if meta.path == DEFAULT {
if meta.input.peek(Token![=]) {
// #[serde(default = "...")]
if let Some(path) = parse_lit_into_expr_path(cx, DEFAULT, &meta)? {
default.set(&meta.path, Default::Path(path));
// #[serde(default = ...)]
if let Some(default_value) = parse_default(cx, &meta)? {
default.set(&meta.path, default_value)
}
} else {
// #[serde(default)]
Expand Down Expand Up @@ -1548,6 +1549,54 @@ fn parse_lit_into_expr_path(
})
}

/// Parses either an [`ExprPath`](syn::ExprPath) to a `fn` which will return the
/// default value for a field, or an [`Expr`](syn::ExprParen) wrapped in parenthesies
/// which is a valid value for a field.
///
/// ```no_run
/// use serde::{Serialize, Deserialize};
///
/// #[derive(Clone, Default, Serialize, Deserialize)]
/// pub struct DemoStruct {
/// #[serde(default = "my_fn")]
/// a: i32,
/// #[serde(default = (12))]
/// b: i32,
/// }
///
/// fn my_fn() -> i32 { 16 }
/// ```
fn parse_default(
cx: &Ctxt,
meta: &ParseNestedMeta,
) -> syn::Result<Option<Default>> {

let expr: syn::Expr = meta.value()?.parse()?;
match expr {
// #[serde(default = "...")]
syn::Expr::Lit(syn::ExprLit { lit: syn::Lit::Str(lit_str), .. }) => {
match lit_str.parse::<syn::ExprPath>() {
Ok(path) => Ok(Some(Default::Path(path))),
_ => {
let msg = format!("failed to parse path: {:?}", lit_str.value());
cx.error_spanned_by(&lit_str, msg);
Ok(None)
}
}
},

// #[serde(default = (...))]
syn::Expr::Paren(paren) => {
Ok(Some(Default::Expr(paren.expr)))
},
_ => {
let msg = format!("failed to parse literal or fn path: {:?}", expr.to_token_stream());
cx.error_spanned_by(&expr, msg);
Ok(None)
}
}
}

fn parse_lit_into_where(
cx: &Ctxt,
attr_name: Symbol,
Expand Down
11 changes: 10 additions & 1 deletion test_suite/tests/test_annotations.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,8 @@ where
a4: D,
#[serde(skip_deserializing, default = "MyDefault::my_default")]
a5: E,
#[serde(skip_deserializing, default = (12.3))]
a6: f32
}

#[derive(Debug, PartialEq, Serialize, Deserialize)]
Expand Down Expand Up @@ -123,6 +125,7 @@ fn test_default_struct() {
a3: 3,
a4: 0,
a5: 123,
a6: 12.3,
},
&[
Token::Struct {
Expand All @@ -139,6 +142,8 @@ fn test_default_struct() {
Token::I32(4),
Token::Str("a5"),
Token::I32(5),
Token::Str("a6"),
Token::F32(12.3),
Token::StructEnd,
],
);
Expand All @@ -150,14 +155,17 @@ fn test_default_struct() {
a3: 123,
a4: 0,
a5: 123,
a6: 12.3
},
&[
Token::Struct {
name: "DefaultStruct",
len: 3,
len: 6,
},
Token::Str("a1"),
Token::I32(1),
Token::Str("a6"),
Token::F32(12.3),
Token::StructEnd,
],
);
Expand Down Expand Up @@ -436,6 +444,7 @@ fn test_ignore_unknown() {
a3: 3,
a4: 0,
a5: 123,
a6: 12.3
},
&[
Token::Struct {
Expand Down
2 changes: 1 addition & 1 deletion test_suite/tests/ui/default-attribute/enum_path.stderr
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
error: #[serde(default = "...")] can only be used on structs
error: #[serde(default = ...)] can only be used on structs
--> tests/ui/default-attribute/enum_path.rs:4:9
|
4 | #[serde(default = "default_e")]
Expand Down