qt-build-utils: split platform linker setup into another module

crates/cxx-qt-build/src/lib.rs

@@ -1120,7 +1120,7 @@ extern "C" bool {init_fun}() {{
         let qt_modules = self.qt_modules(&dependencies);
 
         // Ensure that the linker is setup correctly for Cargo builds
-        qt_build_utils::setup_linker();
+        qt_build_utils::QtPlatformLinker::init();
 
         let header_root = dir::header_root();
 

crates/qt-build-utils/src/lib.rs

@@ -30,6 +30,9 @@ pub use installation::qmake::QtInstallationQMake;
 #[cfg(feature = "qmake")]
 mod parse_cflags;
 
+mod platform;
+pub use platform::QtPlatformLinker;
+
 mod tool;
 pub use tool::{
     MocArguments, MocProducts, QmlCacheArguments, QmlCacheProducts, QtTool, QtToolMoc,
@@ -43,75 +46,10 @@ use std::{
     fs::File,
     io::Write,
     path::{Path, PathBuf},
-    process::Command,
 };
 
 use semver::Version;
 
-fn command_help_output(command: &str) -> std::io::Result<std::process::Output> {
-    Command::new(command).args(["--help"]).output()
-}
-
-/// Linking executables (including tests) with Cargo that link to Qt fails to link with GNU ld.bfd,
-/// which is the default on most Linux distributions, so use GNU ld.gold, lld, or mold instead.
-/// If you are using a C++ build system such as CMake to do the final link of the executable, you do
-/// not need to call this function.
-///
-/// With Apple devices we set -fapple-link-rtlib as we build with -nodefaultlibs
-/// otherwise we cannot user helpers from the compiler runtime in Qt
-///
-/// This does nothing on non-Unix platforms.
-pub fn setup_linker() {
-    if env::var("CARGO_CFG_UNIX").is_err() {
-        return;
-    }
-
-    if let Ok(vendor) = env::var("CARGO_CFG_TARGET_VENDOR") {
-        if vendor == "apple" {
-            // Tell clang link to clang_rt as we build with -nodefaultlibs
-            // otherwise we cannot use helpers from the compiler runtime in Qt
-            println!("cargo::rustc-link-arg=-fapple-link-rtlib");
-        }
-    }
-
-    let flags = env::var("CARGO_ENCODED_RUSTFLAGS").unwrap();
-    // Don't override custom flags
-    if !flags.contains("-fuse-ld") {
-        // ld is the system default linker. On Linux, this is usually GNU ld.bfd, but it may be symlinked to another
-        // linker. On macOS, Xcode ships lld with the executable named ld.
-        let ld_help = String::from_utf8(
-            command_help_output("ld")
-                .expect("Could not run ld command")
-                .stdout,
-        )
-        .unwrap();
-        // bfd supports some exotic targets that other linkers do not.
-        let ld_is_bfd = ld_help.contains("symbolsrec")
-            || ld_help.contains("verilog")
-            || ld_help.contains("tekhex");
-
-        // Whatever linker is being used that's not bfd will likely work.
-        if !ld_is_bfd {
-            return;
-        }
-
-        // mold is fastest, but specifing mold with -fuse-ld requires GCC >= 12 or Clang.
-        // Unfortunately cargo does not provide a means to set the linker driver via build scripts,
-        // so linking would fail trying to use -fuse-ld=mold with GCC < 12 even if clang is installed.
-        // So, prefer lld and gold to mold for robustness on the widest range of systems.
-        // mold can still be used by manually specifying it in ~/.cargo/config.toml or the RUSTFLAGS environment variable.
-        if command_help_output("lld").is_ok() {
-            println!("cargo::rustc-link-arg=-fuse-ld=lld");
-        } else if command_help_output("ld.gold").is_ok() {
-            println!("cargo::rustc-link-arg=-fuse-ld=gold");
-        } else if command_help_output("mold").is_ok() {
-            println!("cargo::rustc-link-arg=-fuse-ld=mold");
-        } else {
-            println!("cargo::warning=Neither mold, lld, nor gold linkers were found. Linking with GNU ld.bfd will likely fail.");
-        }
-    }
-}
-
 /// Paths to C++ files generated by [QtBuild::register_qml_module]
 pub struct QmlModuleRegistrationFiles {
     /// File generated by [rcc](https://doc.qt.io/qt-6/rcc.html) for the QML plugin. The compiled static library

crates/qt-build-utils/src/platform.rs

@@ -0,0 +1,75 @@
+// SPDX-FileCopyrightText: 2025 Klarälvdalens Datakonsult AB, a KDAB Group company <[email protected]>
+// SPDX-FileContributor: Andrew Hayzen <[email protected]>
+//
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+use std::{env, process::Command};
+
+fn command_help_output(command: &str) -> std::io::Result<std::process::Output> {
+    Command::new(command).args(["--help"]).output()
+}
+
+/// Linking executables (including tests) with Cargo that link to Qt fails to link with GNU ld.bfd,
+/// which is the default on most Linux distributions, so use GNU ld.gold, lld, or mold instead.
+/// If you are using a C++ build system such as CMake to do the final link of the executable, you do
+/// not need to call this function.
+///
+/// With Apple devices we set -fapple-link-rtlib as we build with -nodefaultlibs
+/// otherwise we cannot user helpers from the compiler runtime in Qt
+///
+/// This does nothing on non-Unix platforms.
+pub struct QtPlatformLinker;
+
+impl QtPlatformLinker {
+    /// Initialize support for linking executables with Cargo that link to Qt
+    pub fn init() {
+        if env::var("CARGO_CFG_UNIX").is_err() {
+            return;
+        }
+
+        if let Ok(vendor) = env::var("CARGO_CFG_TARGET_VENDOR") {
+            if vendor == "apple" {
+                // Tell clang link to clang_rt as we build with -nodefaultlibs
+                // otherwise we cannot use helpers from the compiler runtime in Qt
+                println!("cargo::rustc-link-arg=-fapple-link-rtlib");
+            }
+        }
+
+        let flags = env::var("CARGO_ENCODED_RUSTFLAGS").unwrap();
+        // Don't override custom flags
+        if !flags.contains("-fuse-ld") {
+            // ld is the system default linker. On Linux, this is usually GNU ld.bfd, but it may be symlinked to another
+            // linker. On macOS, Xcode ships lld with the executable named ld.
+            let ld_help = String::from_utf8(
+                command_help_output("ld")
+                    .expect("Could not run ld command")
+                    .stdout,
+            )
+            .unwrap();
+            // bfd supports some exotic targets that other linkers do not.
+            let ld_is_bfd = ld_help.contains("symbolsrec")
+                || ld_help.contains("verilog")
+                || ld_help.contains("tekhex");
+
+            // Whatever linker is being used that's not bfd will likely work.
+            if !ld_is_bfd {
+                return;
+            }
+
+            // mold is fastest, but specifing mold with -fuse-ld requires GCC >= 12 or Clang.
+            // Unfortunately cargo does not provide a means to set the linker driver via build scripts,
+            // so linking would fail trying to use -fuse-ld=mold with GCC < 12 even if clang is installed.
+            // So, prefer lld and gold to mold for robustness on the widest range of systems.
+            // mold can still be used by manually specifying it in ~/.cargo/config.toml or the RUSTFLAGS environment variable.
+            if command_help_output("lld").is_ok() {
+                println!("cargo::rustc-link-arg=-fuse-ld=lld");
+            } else if command_help_output("ld.gold").is_ok() {
+                println!("cargo::rustc-link-arg=-fuse-ld=gold");
+            } else if command_help_output("mold").is_ok() {
+                println!("cargo::rustc-link-arg=-fuse-ld=mold");
+            } else {
+                println!("cargo::warning=Neither mold, lld, nor gold linkers were found. Linking with GNU ld.bfd will likely fail.");
+            }
+        }
+    }
+}