When building for wasm32v1-none with Cargo, the 'std' feature gets
unified across the dependency graph, meaning serde_core sees
feature="std" even on a no_std target. This caused compilation failures
because the crate tried to use std:: imports.
This commit fixes the issue by checking target_os = "none" in addition
to the std feature flag:
- lib.rs: Force no_std when target_os = "none"
- crate_root.rs: Use core/alloc instead of std on target_os = "none"
- All std-only cfg blocks now include not(target_os = "none")
- Add explicit prelude imports for wasm32v1-none compatibility
When building serde_core for wasm32v1-none target with no_std but with
the alloc feature enabled, the Rust compiler doesn't automatically inject
the prelude. This causes ?Sized bounds to fail with "bound modifier ?
can only be applied to Sized" errors.
This commit adds explicit prelude imports to all modules that:
1. Use `use crate::lib::*;` for serde's internal lib facade
2. Use `?Sized` bounds in their code
The fix adds:
```rust
#[allow(unused_imports)]
#[cfg(not(feature = "std"))]
use ::core::prelude::rust_2021::*;
```
This ensures Sized, Clone, Copy, and other prelude traits are in scope
for the ?Sized syntax to work correctly on wasm32v1-none targets.
Affected files:
- serde_core/src/de/impls.rs
- serde_core/src/de/mod.rs
- serde_core/src/private/doc.rs
- serde_core/src/ser/fmt.rs
- serde_core/src/ser/impls.rs
- serde_core/src/ser/impossible.rs
- serde_core/src/ser/mod.rs
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
This prevents diagnostics being rendered like `serde_core::ser::Serialize`
and `serde_core::de::Deserialize` in projects that have no direct
dependency on serde_core.
The attributes make error messages arguably sometimes worse than
pre-serde_core by always rendering `serde::Serialize` and never
`Serialize` when `use serde::Serialize` is in scope, which rustc's
default message construction knows to recognize. But this is probably
negligible.
I explored the alternative of setting `[lib] name = "serde"` in
serde_core/Cargo.toml which also prevents `serde_core::ser::Serialize`
in messages, but has the unwanted effect of also inserting the following
noise into every such error:
note: there are multiple different versions of crate `serde` in the dependency graph
--> $WORKSPACE/serde_core/src/ser/mod.rs:225:1
|
225 | pub trait Serialize {
| ^^^^^^^^^^^^^^^^^^^ this is the required trait
|
::: src/main.rs:1:1
|
1 | struct MyStruct;
| --------------- this type doesn't implement the required trait
...
4 | let _ = serde_json::to_string(&MyStruct);
| ----------
| |
| one version of crate `serde` used here, as a dependency of crate `serde`
| one version of crate `serde` used here, as a dependency of crate `serde_json`
|
::: $WORKSPACE/serde/src/private/de.rs:2347:1
|
2347 | pub trait IdentifierDeserializer<'de, E: Error> {
| ----------------------------------------------- this is the found trait
= help: you can use `cargo tree` to explore your dependency tree
The "this is the found trait" pointing to `IdentifierDeserializer` seems
like a compiler bug...
pezkuwichain
David Tolnay