feat: add cygwin support

.github/workflows/libloading.yml

@@ -65,6 +65,26 @@ jobs:
         env:
           TARGET: ${{ matrix.rust_target}}
 
+  msys2-test:
+    runs-on: windows-latest
+    strategy:
+      fail-fast: false
+    steps:
+      - uses: actions/checkout@v2
+      - run: rustup install nightly --profile=minimal
+      - run: rustup default nightly
+      - run: rustup component add rust-src
+      - uses: msys2/setup-msys2@v2
+        with:
+          release: false
+          install: gcc
+      - run: echo "INPUT(libmsys-2.0.a)" | Out-File -FilePath "C:\msys64\usr\lib\libcygwin.a"
+      - run: |
+          $env:PATH = "C:\msys64\usr\bin\;$env:PATH"
+          cargo test --target x86_64-pc-cygwin -Zbuild-std
+        env:
+          CARGO_TARGET_X86_64_PC_CYGWIN_LINKER: x86_64-pc-msys-gcc.exe
+
   bare-cross-build:
     runs-on: ubuntu-latest
     strategy:

Cargo.toml

@@ -34,4 +34,7 @@ all-features = true
 rustdoc-args = ["--cfg", "libloading_docs"]
 
 [lints.rust]
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(libloading_docs)'] }
+unexpected_cfgs = { level = "warn", check-cfg = [
+    'cfg(libloading_docs)',
+    'cfg(target_os, values("cygwin"))',
+] }

src/os/unix/consts.rs

@@ -88,6 +88,7 @@ mod posix {
             target_os = "redox",
             target_os = "nto",
             target_os = "hurd",
+            target_os = "cygwin",
         ))] {
             pub(super) const RTLD_LAZY: c_int = 1;
         } else {
@@ -127,6 +128,7 @@ mod posix {
             target_os = "redox",
             target_os = "nto",
             target_os = "hurd",
+            target_os = "cygwin",
         ))] {
             pub(super) const RTLD_NOW: c_int = 2;
         } else if #[cfg(all(target_os = "android",target_pointer_width = "32"))] {
@@ -150,6 +152,7 @@ mod posix {
             target_env = "uclibc",
             all(target_os = "linux", target_arch = "mips"),
             all(target_os = "linux", target_arch = "mips64"),
+            target_os = "cygwin",
         ))] {
             pub(super) const RTLD_GLOBAL: c_int = 4;
         } else if #[cfg(any(
@@ -224,6 +227,7 @@ mod posix {
             target_os = "fuchsia",
             target_os = "redox",
             target_os = "hurd",
+            target_os = "cygwin",
         ))] {
             pub(super) const RTLD_LOCAL: c_int = 0;
         } else {

src/os/unix/mod.rs

@@ -278,7 +278,8 @@ impl Library {
                 target_os = "solaris",
                 target_os = "illumos",
                 target_os = "redox",
-                target_os = "fuchsia"
+                target_os = "fuchsia",
+                target_os = "cygwin",
             ))] {
                 self.get_singlethreaded(symbol)
             } else {

tests/functions.rs

@@ -191,6 +191,8 @@ fn test_static_ptr() {
 // the target. Especially since it is very unlikely to be fixed given the state of support its
 // support.
 #[cfg(not(all(target_arch = "x86", target_os = "windows", target_env = "gnu")))]
+// Cygwin returns errors on `close`.
+#[cfg(not(target_os = "cygwin"))]
 fn manual_close_many_times() {
     make_helpers();
     let join_handles: Vec<_> = (0..16)
@@ -224,6 +226,8 @@ fn library_this_get() {
             .get::<unsafe extern "C" fn()>(b"test_identity_u32")
             .is_err());
         // Something obscure from libc...
+        // Cygwin behaves like Windows so ignore it.
+        #[cfg(not(target_os = "cygwin"))]
         assert!(this.get::<unsafe extern "C" fn()>(b"freopen").is_ok());
     }
 }

tests/library_filename.rs

@@ -2,7 +2,7 @@ extern crate libloading;
 use libloading::library_filename;
 use std::path::Path;
 
-#[cfg(target_os = "windows")]
+#[cfg(any(target_os = "windows", target_os = "cygwin"))]
 const EXPECTED: &str = "audioengine.dll";
 #[cfg(target_os = "linux")]
 const EXPECTED: &str = "libaudioengine.so";