Support building without libstd

.travis.yml

@@ -20,6 +20,22 @@ matrix:
     - rust: nightly
       env:
        - FEATURES='test_low_transition_point'
+    - rust: 1.36.0
+      env: TARGET=thumbv6m-none-eabi
+      before_script:
+        - rustup target add $TARGET
+        - set -ex
+      script:
+        - cargo build -vv --target=$TARGET
+        - cargo build -v -p test-nostd --target=$TARGET
+    - rust: stable
+      env: TARGET=thumbv6m-none-eabi
+      before_script:
+        - rustup target add $TARGET
+        - set -ex
+      script:
+        - cargo build -vv --target=$TARGET
+        - cargo build -v -p test-nostd --target=$TARGET
 branches:
   only:
     - master

Cargo.toml

@@ -21,12 +21,16 @@ This crate was initially published under the name ordermap, but it was renamed t
 indexmap.
 """
 
-keywords = ["hashmap"]
-categories = ["data-structures"]
+keywords = ["hashmap", "no_std"]
+categories = ["data-structures", "no-std"]
+
+build = "build.rs"
 
 [lib]
 bench = false
 
+[build-dependencies]
+autocfg = "0.1.6"
 [dependencies]
 serde = { version = "1.0", optional = true }
 rayon = { version = "1.0", optional = true }
@@ -56,3 +60,6 @@ tag-name = "{{version}}"
 
 [package.metadata.docs.rs]
 features = ["serde-1", "rayon"]
+
+[workspace]
+members = ["test-nostd"]

build.rs

@@ -0,0 +1,7 @@
+extern crate autocfg;
+
+fn main() {
+    let ac = autocfg::new();
+    ac.emit_sysroot_crate("std");
+    autocfg::rerun_path(file!());
+}

src/lib.rs

@@ -1,6 +1,6 @@
-
 #![deny(unsafe_code)]
 #![doc(html_root_url = "https://docs.rs/indexmap/1/")]
+#![cfg_attr(not(has_std), no_std)]
 
 //! [`IndexMap`] is a hash table where the iteration order of the key-value
 //! pairs is independent of the hash values of the keys.
@@ -12,14 +12,53 @@
 //! [`IndexSet`]: set/struct.IndexSet.html
 //!
 //!
+//!
 //! ## Rust Version
 //!
 //! This version of indexmap requires Rust 1.18 or later, or 1.30+ for
-//! development builds.
+//! development builds, and Rust 1.36+ for using with `alloc` (without `std`),
+//! see below.
 //!
 //! The indexmap 1.x release series will use a carefully considered version
 //! upgrade policy, where in a later 1.x version, we will raise the minimum
 //! required Rust version.
+//!
+//! ## No Standard Library Targets
+//!
+//! From Rust 1.36, this crate supports being built without `std`, requiring
+//! `alloc` instead. This is enabled automatically when it is detected that
+//! `std` is not available. There is no crate feature to enable/disable to
+//! trigger this. It can be tested by building for a std-less target.
+//!
+//! - Creating maps and sets using [`new`][IndexMap::new] and
+//! [`with_capacity`][IndexMap::with_capacity] is unavailable without `std`.  
+//!   Use methods [`IndexMap::default`][def],
+//!   [`with_hasher`][IndexMap::with_hasher],
+//!   [`with_capacity_and_hasher`][IndexMap::with_capacity_and_hasher] instead.
+//!   A no-std compatible hasher will be needed as well, for example
+//!   from the crate `twox-hash`.
+//! - Macros [`indexmap!`] and [`indexset!`] are unavailable without `std`.
+//!
+//! [def]: map/struct.IndexMap.html#impl-Default
+
+#[cfg(not(has_std))]
+#[macro_use(vec)]
+extern crate alloc;
+
+#[cfg(not(has_std))]
+pub(crate) mod std {
+    pub use core::*;
+    pub mod alloc {
+        pub use ::alloc::*;
+    }
+    pub mod collections {
+        pub use ::alloc::collections::*;
+    }
+    pub use ::alloc::vec as vec;
+}
+
+#[cfg(not(has_std))]
+use std::vec::Vec;
 
 #[macro_use]
 mod macros;

src/macros.rs

@@ -1,4 +1,5 @@
 
+#[cfg(has_std)]
 #[macro_export(local_inner_macros)]
 /// Create an `IndexMap` from a list of key-value pairs
 ///
@@ -37,6 +38,7 @@ macro_rules! indexmap {
     };
 }
 
+#[cfg(has_std)]
 #[macro_export(local_inner_macros)]
 /// Create an `IndexSet` from a list of values
 ///

src/map.rs

@@ -1,6 +1,11 @@
 //! `IndexMap` is a hash table where the iteration order of the key-value
 //! pairs is independent of the hash values of the keys.
 
+#[cfg(not(has_std))]
+use alloc::boxed::Box;
+#[cfg(not(has_std))]
+use std::vec::Vec;
+
 pub use mutable_keys::MutableKeys;
 
 #[cfg(feature = "rayon")]
@@ -10,9 +15,11 @@ use std::hash::Hash;
 use std::hash::BuildHasher;
 use std::hash::Hasher;
 use std::iter::FromIterator;
-use std::collections::hash_map::RandomState;
 use std::ops::RangeFull;
 
+#[cfg(has_std)]
+use std::collections::hash_map::RandomState;
+
 use std::cmp::{max, Ordering};
 use std::fmt;
 use std::mem::{replace};
@@ -264,10 +271,17 @@ impl<Sz> ShortHashProxy<Sz>
 /// assert_eq!(letters.get(&'y'), None);
 /// ```
 #[derive(Clone)]
+#[cfg(has_std)]
 pub struct IndexMap<K, V, S = RandomState> {
     core: OrderMapCore<K, V>,
     hash_builder: S,
 }
+#[derive(Clone)]
+#[cfg(not(has_std))]
+pub struct IndexMap<K, V, S> {
+    core: OrderMapCore<K, V>,
+    hash_builder: S,
+}
 
 // core of the map that does not depend on S
 #[derive(Clone)]
@@ -379,6 +393,7 @@ macro_rules! probe_loop {
     }
 }
 
+#[cfg(has_std)]
 impl<K, V> IndexMap<K, V> {
     /// Create a new map. (Does not allocate.)
     pub fn new() -> Self {

src/set.rs

@@ -3,8 +3,13 @@
 #[cfg(feature = "rayon")]
 pub use ::rayon::set as rayon;
 
-use std::cmp::Ordering;
+#[cfg(not(has_std))]
+use std::vec::Vec;
+
+#[cfg(has_std)]
 use std::collections::hash_map::RandomState;
+
+use std::cmp::Ordering;
 use std::fmt;
 use std::iter::{FromIterator, Chain};
 use std::hash::{Hash, BuildHasher};
@@ -59,9 +64,15 @@ type Bucket<T> = super::Bucket<T, ()>;
 /// assert!(!letters.contains(&'y'));
 /// ```
 #[derive(Clone)]
+#[cfg(has_std)]
 pub struct IndexSet<T, S = RandomState> {
     map: IndexMap<T, (), S>,
 }
+#[cfg(not(has_std))]
+#[derive(Clone)]
+pub struct IndexSet<T, S> {
+    map: IndexMap<T, (), S>,
+}
 
 impl<T, S> Entries for IndexSet<T, S> {
     type Entry = Bucket<T>;
@@ -99,6 +110,7 @@ impl<T, S> fmt::Debug for IndexSet<T, S>
     }
 }
 
+#[cfg(has_std)]
 impl<T> IndexSet<T> {
     /// Create a new set. (Does not allocate.)
     pub fn new() -> Self {

test-nostd/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "test-nostd"
+version = "0.1.0"
+authors = ["bluss"]
+publish = false
+edition = "2018"
+
+[dependencies]
+indexmap = { path = ".." }
+# no-std compatible hasher
+twox-hash = { version = "1.5", default-features = false }
+
+[dev-dependencies]

test-nostd/src/lib.rs

@@ -0,0 +1,22 @@
+#![no_std]
+
+use indexmap::IndexMap;
+use indexmap::IndexSet;
+use core::hash::BuildHasherDefault;
+use twox_hash::XxHash64;
+type Map<K, V> = IndexMap<K, V, BuildHasherDefault<XxHash64>>;
+type Set<T> = IndexSet<T, BuildHasherDefault<XxHash64>>;
+
+use core::iter::FromIterator;
+
+pub fn test_compile() {
+    let mut map = Map::default();
+    map.insert(1, 1);
+    map.insert(2, 4);
+    for (_, _) in map.iter() { }
+
+    let _map2 = Map::from_iter(Some((1, 1)));
+
+    let mut set = Set::default();
+    set.insert("a");
+}