jonasbb · jonasbb · Aug 9, 2026 · Aug 9, 2026
diff --git a/serde_with/CHANGELOG.md b/serde_with/CHANGELOG.md
@@ -12,6 +12,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 * Update `syn` and `darling` dependencies to use `syn` v3 (#992)
 * Update dev-dependencies to newer versions (#993)
 * Update `base64` to a newer version. This should not have any API change, but some error messages might change. (#993)
+* `serde_as` can now parse `cfg_attr(true, ...)` and `cfg_attr(false, ...)` (#995)
+    `true`/`false` are new literals as of Rust 1.88 but need to be parsed explicitly with the `syn` types.
+    This is used when emitting `schemars` annotations.
 
 ## [3.22.0] - 2026-08-09
 

diff --git a/serde_with/src/guide/serde_as.md b/serde_with/src/guide/serde_as.md
@@ -148,7 +148,7 @@ Our goal is to serialize this `Data` struct.
 Currently, we do not have anything we can use to replace `???` with, since `_` only works if `RemoteType` would implement `Serialize`, which it does not.
 
 ```rust
-# #[cfg(any())] {
+# #[cfg(false)] {
 #[serde_as]
 #[derive(serde::Serialize)]
 struct Data {
@@ -163,7 +163,7 @@ The `SerializeAs` implementation is **always** written for a local type.
 This allows it to seamlessly work with types from dependencies without running into orphan rule problems.
 
 ```rust
-# #[cfg(any())] {
+# #[cfg(false)] {
 struct LocalType;
 
 impl SerializeAs<RemoteType> for LocalType {
@@ -192,7 +192,7 @@ As can be seen, this is mostly boilerplate, since the most part is encapsulated
 The final `Data` struct will now look like:
 
 ```rust
-# #[cfg(any())] {
+# #[cfg(false)] {
 #[serde_as]
 #[derive(serde::Serialize)]
 struct Data {
@@ -209,7 +209,7 @@ This is a special functionality of serde, where it derives the de/serialization
 You can find all the details in the [official serde documentation](https://serde.rs/remote-derive.html).
 
 ```rust
-# #[cfg(any())] {
+# #[cfg(false)] {
 // Pretend that this is somebody else's crate, not a module.
 mod other_crate {
     // Neither Serde nor the other crate provides Serialize and Deserialize
@@ -242,7 +242,7 @@ We can write this implementation.
 The implementation for `DeserializeAs` works analogue.
 
 ```rust
-# #[cfg(any())] {
+# #[cfg(false)] {
 impl SerializeAs<Duration> for DurationDef {
     fn serialize_as<S>(value: &Duration, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -257,7 +257,7 @@ impl SerializeAs<Duration> for DurationDef {
 This now allows us to use `Duration` for serialization.
 
 ```rust
-# #[cfg(any())] {
+# #[cfg(false)] {
 use other_crate::Duration;
 
 #[serde_as]

diff --git a/serde_with/src/lib.rs b/serde_with/src/lib.rs
@@ -1857,7 +1857,7 @@ pub struct PickFirst<T>(PhantomData<T>);
 /// Deserializing works analogue, by deserializing a `T` and then converting into `O`.
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// struct S {
 ///     #[serde_as(as = "FromInto<T>")]
 ///     value: O,
@@ -1939,7 +1939,7 @@ pub struct FromInto<T>(PhantomData<T>);
 /// Deserializing works analogue, by deserializing a `T` and then converting into `O`.
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// struct S {
 ///     #[serde_as(as = "FromIntoRef<T>")]
 ///     value: O,
@@ -2020,7 +2020,7 @@ pub struct FromIntoRef<T>(PhantomData<T>);
 /// Deserializing works analogue, by deserializing a `T` and then converting into `O`.
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// struct S {
 ///     #[serde_as(as = "TryFromInto<T>")]
 ///     value: O,
@@ -2109,7 +2109,7 @@ pub struct TryFromInto<T>(PhantomData<T>);
 /// Deserializing works analogue, by deserializing a `T` and then converting into `O`.
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// struct S {
 ///     #[serde_as(as = "TryFromIntoRef<T>")]
 ///     value: O,

diff --git a/serde_with/src/rust.rs b/serde_with/src/rust.rs
@@ -18,7 +18,7 @@ use crate::prelude::*;
 /// This cannot work, since there is no way to tell the `Vec` to skip the inner `DoubleOption` if it is `None`.
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// # struct Foobar {
 /// #[serde_as(as = "Vec<DoubleOption<_>>")]
 /// data: Vec<Option<Option<i32>>>,
@@ -182,7 +182,7 @@ pub mod unwrap_or_skip {
 /// The `_` is a placeholder which works for any type which implements [`Serialize`]/[`Deserialize`].
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// #[serde_as]
 /// #[derive(Deserialize, Serialize)]
 /// struct A {
@@ -298,7 +298,7 @@ pub mod sets_duplicate_value_is_error {
 /// The `_` is a placeholder which works for any type which implements [`Serialize`]/[`Deserialize`].
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// #[serde_as]
 /// #[derive(Deserialize, Serialize)]
 /// struct A {
@@ -418,7 +418,7 @@ pub mod maps_duplicate_key_is_error {
 /// The `_` is a placeholder which works for any type which implements [`Serialize`]/[`Deserialize`].
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// #[serde_as]
 /// #[derive(Deserialize, Serialize)]
 /// struct A {
@@ -506,7 +506,7 @@ pub mod sets_last_value_wins {
 /// The `_` is a placeholder which works for any type which implements [`Serialize`]/[`Deserialize`].
 ///
 /// ```rust
-/// # #[cfg(any())] {
+/// # #[cfg(false)] {
 /// #[serde_as]
 /// #[derive(Deserialize, Serialize)]
 /// struct A {

diff --git a/serde_with/tests/schemars_0_8/main.rs b/serde_with/tests/schemars_0_8/main.rs
@@ -132,8 +132,8 @@ fn schemars_other_cfg_attrs() {
     #[derive(JsonSchema, Serialize)]
     struct Test {
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), arbitrary("some" |weird| syntax::<bool, 2>()))]
-        #[cfg_attr(any(), schemars(with = "i32"))]
+        #[cfg_attr(false, arbitrary("some" |weird| syntax::<bool, 2>()))]
+        #[cfg_attr(false, schemars(with = "i32"))]
         custom: i32,
     }
 
@@ -152,11 +152,11 @@ fn schemars_custom_with() {
         custom: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), schemars(with = "i32"))]
+        #[cfg_attr(false, schemars(with = "i32"))]
         with_disabled: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(all(), schemars(with = "i32"))]
+        #[cfg_attr(true, schemars(with = "i32"))]
         always_enabled: i32,
     }
 
@@ -226,11 +226,11 @@ fn schemars_custom_schema_with() {
         custom: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), schemars(schema_with = "custom_int"))]
+        #[cfg_attr(false, schemars(schema_with = "custom_int"))]
         with_disabled: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(all(), schemars(schema_with = "custom_int"))]
+        #[cfg_attr(true, schemars(schema_with = "custom_int"))]
         always_enabled: i32,
     }
 
@@ -494,7 +494,7 @@ mod derive {
 
     #[serde_as]
     #[derive(Serialize)]
-    #[cfg_attr(all(), derive(JsonSchema))]
+    #[cfg_attr(true, derive(JsonSchema))]
     struct Enabled {
         #[serde_as(as = "DisplayFromStr")]
         field: u32,
@@ -503,7 +503,7 @@ mod derive {
     #[allow(dead_code)]
     #[serde_as]
     #[derive(Serialize)]
-    #[cfg_attr(any(), derive(JsonSchema))]
+    #[cfg_attr(false, derive(JsonSchema))]
     struct Disabled {
         // If we are incorrectly adding `#[schemars(with = ...)]` attributes
         // then we should get an error on this field.

diff --git a/serde_with/tests/schemars_0_9/main.rs b/serde_with/tests/schemars_0_9/main.rs
@@ -133,8 +133,8 @@ fn schemars_other_cfg_attrs() {
     #[derive(JsonSchema, Serialize)]
     struct Test {
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), arbitrary("some" |weird| syntax::<bool, 2>()))]
-        #[cfg_attr(any(), schemars(with = "i32"))]
+        #[cfg_attr(false, arbitrary("some" |weird| syntax::<bool, 2>()))]
+        #[cfg_attr(false, schemars(with = "i32"))]
         custom: i32,
     }
 
@@ -153,11 +153,11 @@ fn schemars_custom_with() {
         custom: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), schemars(with = "i32"))]
+        #[cfg_attr(false, schemars(with = "i32"))]
         with_disabled: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(all(), schemars(with = "i32"))]
+        #[cfg_attr(true, schemars(with = "i32"))]
         always_enabled: i32,
     }
 
@@ -225,11 +225,11 @@ fn schemars_custom_schema_with() {
         custom: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), schemars(schema_with = "custom_int"))]
+        #[cfg_attr(false, schemars(schema_with = "custom_int"))]
         with_disabled: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(all(), schemars(schema_with = "custom_int"))]
+        #[cfg_attr(true, schemars(schema_with = "custom_int"))]
         always_enabled: i32,
     }
 
@@ -493,7 +493,7 @@ mod derive {
 
     #[serde_as]
     #[derive(Serialize)]
-    #[cfg_attr(all(), derive(JsonSchema))]
+    #[cfg_attr(true, derive(JsonSchema))]
     struct Enabled {
         #[serde_as(as = "DisplayFromStr")]
         field: u32,
@@ -502,7 +502,7 @@ mod derive {
     #[allow(dead_code)]
     #[serde_as]
     #[derive(Serialize)]
-    #[cfg_attr(any(), derive(JsonSchema))]
+    #[cfg_attr(false, derive(JsonSchema))]
     struct Disabled {
         // If we are incorrectly adding `#[schemars(with = ...)]` attributes
         // then we should get an error on this field.

diff --git a/serde_with/tests/schemars_1/main.rs b/serde_with/tests/schemars_1/main.rs
@@ -133,8 +133,8 @@ fn schemars_other_cfg_attrs() {
     #[derive(JsonSchema, Serialize)]
     struct Test {
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), arbitrary("some" |weird| syntax::<bool, 2>()))]
-        #[cfg_attr(any(), schemars(with = "i32"))]
+        #[cfg_attr(false, arbitrary("some" |weird| syntax::<bool, 2>()))]
+        #[cfg_attr(false, schemars(with = "i32"))]
         custom: i32,
     }
 
@@ -153,11 +153,11 @@ fn schemars_custom_with() {
         custom: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), schemars(with = "i32"))]
+        #[cfg_attr(false, schemars(with = "i32"))]
         with_disabled: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(all(), schemars(with = "i32"))]
+        #[cfg_attr(true, schemars(with = "i32"))]
         always_enabled: i32,
     }
 
@@ -217,11 +217,11 @@ fn schemars_custom_schema_with() {
         custom: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(any(), schemars(schema_with = "custom_int"))]
+        #[cfg_attr(false, schemars(schema_with = "custom_int"))]
         with_disabled: i32,
 
         #[serde_as(as = "DisplayFromStr")]
-        #[cfg_attr(all(), schemars(schema_with = "custom_int"))]
+        #[cfg_attr(true, schemars(schema_with = "custom_int"))]
         always_enabled: i32,
     }
 
@@ -492,7 +492,7 @@ mod derive {
 
     #[serde_as]
     #[derive(Serialize)]
-    #[cfg_attr(all(), derive(JsonSchema))]
+    #[cfg_attr(true, derive(JsonSchema))]
     struct Enabled {
         #[serde_as(as = "DisplayFromStr")]
         field: u32,
@@ -501,7 +501,7 @@ mod derive {
     #[allow(dead_code)]
     #[serde_as]
     #[derive(Serialize)]
-    #[cfg_attr(any(), derive(JsonSchema))]
+    #[cfg_attr(false, derive(JsonSchema))]
     struct Disabled {
         // If we are incorrectly adding `#[schemars(with = ...)]` attributes
         // then we should get an error on this field.

diff --git a/serde_with_macros/CHANGELOG.md b/serde_with_macros/CHANGELOG.md
@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 
 * Update `syn` and `darling` dependencies to use `syn` v3 (#992)
+* `serde_as` can now parse `cfg_attr(true, ...)` and `cfg_attr(false, ...)` (#995)
+    `true`/`false` are new literals as of Rust 1.88 but need to be parsed explicitly with the `syn` types.
+    This is used when emitting `schemars` annotations.
 
 ## [3.22.0] - 2026-08-09