libvlc-sys: import libvlc via raw-dylib on Windows

Windows has no import library to link against: the VLC installer and
.zip ship libvlc.dll but no .lib. Previous workaround was to use vswhom
+ dumpbin + lib.exe to synthesise one at build time from the DLL's
exports.

rustc's `raw-dylib` linkage removes the need entirely, it generates the
imports straight from the DLL name.

Cargo.lock

@@ -2,22 +2,6 @@
 # It is not intended for manual editing.
 version = 3
 
-[[package]]
-name = "cc"
-version = "1.4.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "509591b7bcd67f4ef775afad7662703b4935daaa6ec0e5605cfb1090b32a2b6d"
-dependencies = [
- "find-msvc-tools",
- "shlex",
-]
-
-[[package]]
-name = "find-msvc-tools"
-version = "0.1.11"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d45db016d36b838f563236e9193d0ee6ce38f3f68b6c94e914b4929c96bbb890"
-
 [[package]]
 name = "libc"
 version = "0.2.189"
@@ -30,7 +14,6 @@ version = "0.2.0"
 dependencies = [
  "libc",
  "pkg-config",
- "vswhom",
 ]
 
 [[package]]
@@ -39,12 +22,6 @@ version = "0.3.34"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f6b464fbc74e149a392436b17d523f769e057cb6877f6a5c4618bc6f11800548"
 
-[[package]]
-name = "shlex"
-version = "2.0.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f8fadd59c855ef2080decdef8ff161eb6661b86933c9d82e5ba29dc602a55aba"
-
 [[package]]
 name = "vlc-rs"
 version = "0.3.0"
@@ -52,23 +29,3 @@ dependencies = [
  "libc",
  "libvlc-sys",
 ]
-
-[[package]]
-name = "vswhom"
-version = "0.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "be979b7f07507105799e854203b470ff7c78a1639e330a58f183b5fea574608b"
-dependencies = [
- "libc",
- "vswhom-sys",
-]
-
-[[package]]
-name = "vswhom-sys"
-version = "0.1.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fb067e4cbd1ff067d1df46c9194b5de0e98efd2810bbc95c5d5e5f25a3231150"
-dependencies = [
- "cc",
- "libc",
-]

libvlc-sys/Cargo.toml

@@ -23,6 +23,3 @@ libc = "0.2"
 
 [build-dependencies]
 pkg-config = "0.3"
-
-[target.'cfg(target_os = "windows")'.build-dependencies]
-vswhom = "0.1.0"

libvlc-sys/bindings.rs

@@ -1610,6 +1610,7 @@ const _: () = {
     ["Offset of field: libvlc_log_message_t::psz_message"]
         [::core::mem::offset_of!(libvlc_log_message_t, psz_message) - 32usize];
 };
+#[cfg_attr(windows, link(name = "libvlc", kind = "raw-dylib"))]
 unsafe extern "C" {
     pub fn libvlc_errmsg() -> *const libc::c_char;
     pub fn libvlc_clearerr();

libvlc-sys/build.rs

@@ -1,5 +1,7 @@
 //! Build script for `libvlc-sys`, locates and links libvlc.
 
+use std::env;
+
 /// Minimum supported libvlc version.
 const MIN_LIBVLC_VERSION: &str = "3.0.0";
 
@@ -10,126 +12,21 @@ fn probe_libvlc() -> Result<pkg_config::Library, pkg_config::Error> {
         .probe("libvlc")
 }
 
-#[cfg(target_os = "windows")]
+fn main() {
-mod windows {
+    // vsnprintf is inlined by the UCRT headers, so MSVC needs this to resolve
-    #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
+    // the symbol src/lib.rs declares. https://stackoverflow.com/a/34230122
-    compile_error!("Only x86 and x86_64 are supported at the moment. Adding support for other architectures should be trivial.");
+    if env::var("CARGO_CFG_TARGET_ENV").unwrap_or_default() == "msvc" {
-
-    use std::env;
-    use std::ffi::OsString;
-    use std::fs;
-    use std::path::{Path, PathBuf};
-    use std::process::Command;
-
-    use vswhom::VsFindResult;
-
-    pub fn link_vlc() {
-        let vlc_path = vlc_path();
-
-        let out_dir = PathBuf::from(env::var_os("OUT_DIR").unwrap());
-
-        let vs = VsFindResult::search().expect("Could not locate Visual Studio");
-        let vs_exe_path = PathBuf::from(
-            vs.vs_exe_path
-                .expect("Could not retrieve executable path for Visual Studio"),
-        );
-
-        generate_lib_from_dll(&out_dir, &vs_exe_path, &vlc_path);
-        println!("cargo:rustc-link-search=native={}", out_dir.display());
-        // NOTE: Without this directive, linking fails with:
-        //       ```
-        //       error LNK2019: unresolved external symbol vsnprintf referenced in function _{MangledSymbolName}
-        //          msvcrt.lib(vsnprintf.obj) : error LNK2001: unresolved external symbol vsnprintf
-        //          msvcrt.lib(vsnprintf.obj) : error LNK2001: unresolved external symbol _vsnprintf
-        //       ```
-        //       https://stackoverflow.com/a/34230122
         println!("cargo:rustc-link-lib=dylib=legacy_stdio_definitions");
     }
 
-    fn generate_lib_from_dll(out_dir: &Path, vs_exe_path: &Path, vlc_path: &Path) {
+    // The bindings import from libvlc.dll directly via `raw-dylib`, so
-        // https://wiki.videolan.org/GenerateLibFromDll/
+    // Windows needs neither an import library nor a search path,
-
+    // only the DLL at runtime.
-        let vs_dumpbin = vs_exe_path.join("dumpbin.exe");
+    if env::var("CARGO_CFG_TARGET_OS").unwrap() == "windows" {
-        let vs_lib = vs_exe_path.join("lib.exe");
+        return;
-        let vlc_def_path = out_dir.join("libvlc.def");
-        let vlc_import_lib = out_dir.join("vlc.lib");
-
-        let libvlc = vlc_path.join("libvlc.dll");
-        let exports = Command::new(vs_dumpbin)
-            .current_dir(out_dir)
-            .arg("/EXPORTS")
-            .arg(libvlc.display().to_string().trim_end_matches(r"\"))
-            .output()
-            .unwrap();
-        let exports = String::from_utf8(exports.stdout).unwrap();
-
-        let mut vlc_def = String::from("EXPORTS\n");
-        for line in exports.lines() {
-            if let Some(line) = line.get(26..) {
-                if line.starts_with("libvlc_") {
-                    vlc_def.push_str(line);
-                    vlc_def.push_str("\r\n");
-                }
-            }
-        }
-        fs::write(&vlc_def_path, vlc_def.into_bytes()).unwrap();
-
-        // FIXME: Handle paths with spaces in them.
-        Command::new(vs_lib)
-            .current_dir(out_dir)
-            .arg("/NOLOGO")
-            .args(&[
-                format!(
-                    r#"/DEF:{}"#,
-                    vlc_def_path.display().to_string().trim_end_matches(r"\")
-                ),
-                format!(
-                    r#"/OUT:{}"#,
-                    vlc_import_lib.display().to_string().trim_end_matches(r"\")
-                ),
-                format!(
-                    "/MACHINE:{}",
-                    match target_arch().as_str() {
-                        "x86" => "x86",
-                        "x86_64" => "x64",
-                        _ => unreachable!(),
-                    }
-                ),
-            ])
-            .status()
-            .expect("Failed to run lib.exe")
-            .success()
-            .then_some(())
-            .expect("lib.exe failed to generate the vlc import library");
     }
 
-    fn vlc_path() -> PathBuf {
-        #[allow(unused_assignments)]
-        let arch_path: Option<OsString> = match target_arch().as_str() {
-            "x86" => env::var_os("VLC_LIB_DIR_X86"),
-            "x86_64" => env::var_os("VLC_LIB_DIR_X86_64"),
-            _ => unreachable!(),
-        };
-
-        arch_path
-            .or_else(|| env::var_os("VLC_LIB_DIR"))
-            .map(PathBuf::from)
-            .expect("VLC_LIB_DIR not set")
-    }
-
-    fn target_arch() -> String {
-        env::var("CARGO_CFG_TARGET_ARCH").unwrap()
-    }
-}
-
-fn main() {
-    // On success pkg-config has already emitted the link directives; only the
-    // failure path needs handling.
     if let Err(err) = probe_libvlc() {
-        #[cfg(target_os = "windows")]
-        windows::link_vlc();
-
-        #[cfg(not(target_os = "windows"))]
         panic!("libvlc (>= {}) not found: {:?}", MIN_LIBVLC_VERSION, err);
     }
 }

xtask/src/main.rs

@@ -73,6 +73,13 @@ fn generate_bindings() {
         "a va_list spelling we do not know about survived"
     );
 
+    // On Windows rustc can synthesise the imports straight from the DLL, so no
+    // import library is needed. bindgen cannot emit the attribute itself.
+    let generated = generated.replace(
+        "unsafe extern \"C\" {",
+        "#[cfg_attr(windows, link(name = \"libvlc\", kind = \"raw-dylib\"))]\nunsafe extern \"C\" {",
+    );
+
     std::fs::write(&output, generated).expect("couldn't write bindings");
     println!("wrote {}", output.display());
 }