no_std support

Cargo.toml

@@ -22,6 +22,10 @@ exclude = [
     ".gitignore",
 ]
 
+[features]
+default = ["std"]
+std = []
+
 [dependencies]
 serde = { version = "^1.0.80", default-features = false, features = ["alloc"] }
 

rust-toolchain.toml

@@ -0,0 +1,11 @@
+[toolchain]
+channel = "nightly-2022-11-17"
+components = [
+  "rust-src",
+  "cargo",
+]
+targets = [
+  "wasm32-unknown-unknown",
+  # that is the way to test that it checks and builds againt no_std target
+  "thumbv7em-none-eabi"
+  ]

shell.nix

@@ -0,0 +1,23 @@
+{ pkgs ? import <nixpkgs> { overlays = [ (import (builtins.fetchTarball "https://github.com/oxalica/rust-overlay/archive/refs/heads/stable.zip")) ]; } }:
+let
+  rust-as-on-ci = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+  package = "serde-json-wasm";
+  check-no-std = pkgs.writeShellApplication rec {
+    name = "check-no-std";
+    runtimeInputs = [ rust-as-on-ci ];
+    text = ''
+      cargo build --no-default-features --target thumbv7em-none-eabi --package ${package}
+      cargo build --no-default-features --target wasm32-unknown-unknown --package ${package}
+    '';
+  };
+  check-wasm-std = pkgs.writeShellApplication rec {
+    name = "check-wasm-std";
+    runtimeInputs = [ rust-as-on-ci ];
+    text = ''
+      cargo build --target wasm32-unknown-unknown --locked --package ${package} --features std
+    '';
+  };
+in
+pkgs.mkShell {
+  nativeBuildInputs = [ rust-as-on-ci check-no-std check-wasm-std];
+}

src/de/errors.rs

@@ -1,5 +1,6 @@
+use crate::no_std::prelude::*;
+use crate::no_std::{error, fmt};
 use serde::de;
-use std::{error, fmt};
 
 /// Deserialization result
 pub type Result<T> = core::result::Result<T, Error>;

src/de/mod.rs

@@ -13,7 +13,8 @@ use serde::de::{self, Visitor};
 use self::enum_::{StructVariantAccess, UnitVariantAccess};
 use self::map::MapAccess;
 use self::seq::SeqAccess;
-use std::str::from_utf8;
+use crate::no_std::prelude::*;
+use crate::no_std::str::from_utf8;
 
 /// Deserializer will parse serde-json-wasm flavored JSON into a
 /// serde-annotated struct

src/de/unescape.rs

@@ -1,4 +1,5 @@
-use std::convert::TryFrom;
+use crate::no_std::convert::TryFrom;
+use crate::no_std::prelude::*;
 
 use super::errors::{Error, Result};
 

src/lib.rs

@@ -54,8 +54,14 @@
 #![deny(missing_docs)]
 #![deny(rust_2018_compatibility)]
 #![deny(rust_2018_idioms)]
+#![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(not(feature = "std"), feature(error_in_core))]
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
 
 pub mod de;
+mod no_std;
 pub mod ser;
 
 #[doc(inline)]

src/no_std.rs

@@ -0,0 +1,109 @@
+//! if somebody will need alternative implementation, for example for collection or fmt, one may patch for himself this one
+
+#[cfg(feature = "std")]
+pub use std::vec;
+
+#[cfg(not(feature = "std"))]
+pub use alloc::vec;
+
+#[cfg(not(feature = "std"))]
+pub use core::mem;
+#[cfg(feature = "std")]
+pub use std::mem;
+
+#[cfg(not(feature = "std"))]
+pub use core::result;
+#[cfg(feature = "std")]
+pub use std::result;
+
+#[cfg(not(feature = "std"))]
+pub use core::cmp;
+#[cfg(feature = "std")]
+pub use std::cmp;
+
+#[cfg(not(feature = "std"))]
+pub use core::error;
+#[cfg(feature = "std")]
+pub use std::error;
+
+#[cfg(feature = "std")]
+pub use std::iter;
+
+#[cfg(not(feature = "std"))]
+pub use core::iter;
+
+#[cfg(feature = "std")]
+pub use std::ops;
+
+#[cfg(not(feature = "std"))]
+pub use core::ops;
+
+#[cfg(feature = "std")]
+pub use std::string;
+
+#[cfg(not(feature = "std"))]
+pub use alloc::string;
+
+pub mod array {
+    #[cfg(feature = "std")]
+    pub use std::array::TryFromSliceError;
+
+    #[cfg(not(feature = "std"))]
+    pub use core::array::TryFromSliceError;
+}
+
+#[cfg(feature = "std")]
+pub use std::convert;
+
+#[cfg(not(feature = "std"))]
+pub use core::convert;
+
+#[cfg(feature = "std")]
+pub use std::collections;
+
+#[cfg(not(feature = "std"))]
+pub use alloc::collections;
+
+#[cfg(feature = "std")]
+pub use std::fmt;
+
+#[cfg(not(feature = "std"))]
+pub use alloc::fmt;
+
+pub mod borrow {
+    #[cfg(feature = "std")]
+    pub use std::borrow::Cow;
+
+    #[cfg(not(feature = "std"))]
+    pub use alloc::borrow::Cow;
+}
+
+#[cfg(feature = "std")]
+pub use std::str;
+
+#[cfg(not(feature = "std"))]
+pub use alloc::str;
+
+#[cfg(feature = "std")]
+pub use std::marker;
+
+#[cfg(not(feature = "std"))]
+pub use core::marker;
+
+pub mod any {
+    #[cfg(feature = "std")]
+    pub use std::any::type_name;
+
+    #[cfg(not(feature = "std"))]
+    pub use core::any::type_name;
+}
+
+// just because it is default prelude
+pub mod prelude {
+    pub use super::{
+        marker::{Send, Sync},
+        result::Result::{Err, Ok},
+        string::{String, ToString},
+        vec::Vec,
+    };
+}

src/ser/map.rs

@@ -1,4 +1,5 @@
-use std::fmt;
+use crate::no_std::fmt;
+use crate::no_std::prelude::*;
 
 use serde::{ser, Serialize};
 

src/ser/mod.rs

@@ -1,10 +1,11 @@
 //! Serialize a Rust data structure into JSON data
 
-use std::{error, fmt};
+use crate::no_std::prelude::*;
+use crate::no_std::{error, fmt};
 
 use serde::ser;
 
-use std::vec::Vec;
+use crate::no_std::vec::Vec;
 
 use self::map::SerializeMap;
 use self::seq::SerializeSeq;