add no-std support

Author: AlexanderSchuetz97

.github/workflows/libloading.yml

@@ -33,6 +33,19 @@ jobs:
         # pwsh.exe drops quotes kekw. https://stackoverflow.com/a/59036879
         shell: bash
 
+  no-std-build-test:
+    runs-on: ubuntu-latest
+    # This will rebuild core and alloc, which will re-mangle symbols in alloc,
+    # which then will break the pre-compiled std. This will cause the program to fail to link.
+    # This test does not test anything in an actual no-std environment only that the library compiles on it.
+    # We test all no-std only functions together with the ordinary functions.
+    steps:
+      - uses: actions/checkout@v4
+      - name: Add nightly toolchain
+        run: rustup component add rust-src --toolchain nightly-x86_64-unknown-linux-gnu
+      - name: Compile without the standard library
+        run: cargo clean && cargo +nightly build -Zbuild-std=core,alloc --no-default-features
+
   windows-test:
     runs-on: windows-latest
     strategy:

Cargo.toml

@@ -15,6 +15,10 @@ categories = ["api-bindings"]
 rust-version = "1.71.0"
 edition = "2015"
 
+[features]
+default = ["std"]
+std = []
+
 [target.'cfg(windows)'.dependencies.windows-link]
 version = "0.2"
 

src/error.rs

@@ -1,11 +1,12 @@
-use std::ffi::{CStr, CString};
+use alloc::ffi::CString;
+use core::ffi::CStr;
 
 /// A `dlerror` error.
 pub struct DlDescription(pub(crate) CString);
 
-impl std::fmt::Debug for DlDescription {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        std::fmt::Debug::fmt(&self.0, f)
+impl core::fmt::Debug for DlDescription {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        core::fmt::Debug::fmt(&self.0, f)
     }
 }
 
@@ -16,11 +17,15 @@ impl From<&CStr> for DlDescription {
 }
 
 /// A Windows API error.
+#[cfg(not(feature = "std"))]
+pub struct WindowsError(pub(crate) i32);
+
+#[cfg(feature = "std")]
 pub struct WindowsError(pub(crate) std::io::Error);
 
-impl std::fmt::Debug for WindowsError {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        std::fmt::Debug::fmt(&self.0, f)
+impl core::fmt::Debug for WindowsError {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        core::fmt::Debug::fmt(&self.0, f)
     }
 }
 
@@ -82,17 +87,28 @@ pub enum Error {
     /// Could not create a new CString.
     CreateCString {
         /// The source error.
-        source: std::ffi::NulError,
+        source: alloc::ffi::NulError,
     },
     /// Could not create a new CString from bytes with trailing null.
     CreateCStringWithTrailing {
         /// The source error.
-        source: std::ffi::FromBytesWithNulError,
+        source: core::ffi::FromBytesWithNulError,
     },
 }
 
-impl std::error::Error for Error {
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+impl core::error::Error for Error {
+    #[cfg(not(feature = "std"))]
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
+        use Error::*;
+        match *self {
+            CreateCString { ref source } => Some(source),
+            CreateCStringWithTrailing { ref source } => Some(source),
+            _ => None,
+        }
+    }
+
+    #[cfg(feature = "std")]
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
         use Error::*;
         match *self {
             CreateCString { ref source } => Some(source),
@@ -106,8 +122,8 @@ impl std::error::Error for Error {
     }
 }
 
-impl std::fmt::Display for Error {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Display for Error {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
         use Error::*;
         match *self {
             DlOpen { ref desc } => write!(f, "{}", desc.0.to_string_lossy()),

src/lib.rs

@@ -40,6 +40,11 @@
     deny(missing_docs, clippy::all, unreachable_pub, unused)
 )]
 #![cfg_attr(libloading_docs, feature(doc_cfg))]
+#![no_std]
+
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std;
 
 pub mod changelog;
 mod error;
@@ -51,7 +56,10 @@ mod util;
 pub use self::error::Error;
 #[cfg(any(unix, windows, libloading_docs))]
 pub use self::safe::{Library, Symbol};
+
+#[cfg(feature = "std")]
 use std::env::consts::{DLL_PREFIX, DLL_SUFFIX};
+#[cfg(feature = "std")]
 use std::ffi::{OsStr, OsString};
 
 /// Converts a library name to a filename generally appropriate for use on the system.
@@ -71,6 +79,7 @@ use std::ffi::{OsStr, OsString};
 ///     Library::new(library_filename("LLVM"))
 /// };
 /// ```
+#[cfg(feature = "std")]
 pub fn library_filename<S: AsRef<OsStr>>(name: S) -> OsString {
     let name = name.as_ref();
     let mut string = OsString::with_capacity(name.len() + DLL_PREFIX.len() + DLL_SUFFIX.len());

src/os/unix/consts.rs

@@ -1,4 +1,4 @@
-use std::os::raw::c_int;
+use core::ffi::c_int;
 
 /// Perform lazy binding.
 ///