cxx-qt-lib: use +whole_archive for std_types so that cargo-only works

When building with cargo we need to ensure that the statics aren't
optimised out for registering types with Qt 5.

Otherwise we cannot use numbers in QML.

Also move std_types from -lib into -build, which potentially allows
us to have cxx-qt-lib separate in the future.

Closes KDAB#592

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

@@ -389,12 +389,11 @@ impl CxxQtBuilder {
         // Ensure that the linker is setup correctly for Cargo builds
         qt_build_utils::setup_linker();
 
-        let out_dir = env::var("OUT_DIR").unwrap();
         // The include directory needs to be namespaced by crate name when exporting for a C++ build system,
         // but for using cargo build without a C++ build system, OUT_DIR is already namespaced by crate name.
         let header_root = match env::var("CXXQT_EXPORT_DIR") {
             Ok(export_dir) => format!("{export_dir}/{}", env::var("CARGO_PKG_NAME").unwrap()),
-            Err(_) => out_dir,
+            Err(_) => env::var("OUT_DIR").unwrap(),
         };
         let generated_header_dir = format!("{header_root}/cxx-qt-gen");
 
@@ -429,6 +428,7 @@ impl CxxQtBuilder {
         // https://github.com/rust-lang/rust/issues/110912
         cc_builder_whole_archive.link_lib_modifier("-bundle");
         for builder in [&mut self.cc_builder, &mut cc_builder_whole_archive] {
+            // Note, ensure our settings stay in sync across cxx-qt-build and cxx-qt-lib
             builder.cpp(true);
             // MSVC
             builder.flag_if_supported("/std:c++17");
@@ -506,6 +506,33 @@ impl CxxQtBuilder {
             cc_builder_whole_archive.file(qtbuild.qrc(&qrc_file));
             cc_builder_whole_archive_files_added = true;
         }
+
+        // If we are using Qt 5 then write the std_types source
+        // This registers std numbers as a type for use in QML
+        //
+        // Note that we need this to be compiled into the whole_archive builder
+        // as they are stored in statics in the source.
+        if qtbuild.version().major == 5 {
+            let std_types_contents = include_str!("std_types_qt5.cpp");
+            let std_types_path = format!(
+                "{out_dir}/std_types_qt5.cpp",
+                out_dir = env::var("OUT_DIR").unwrap()
+            );
+            let mut source =
+                File::create(&std_types_path).expect("Could not create std_types source");
+            write!(source, "{std_types_contents}").expect("Could not write std_types source");
+
+            cc_builder_whole_archive.file(&std_types_path);
+            cc_builder_whole_archive_files_added = true;
+            // Note we need to have std_types in the cc_builder for CMake builds to work.
+            //
+            // This is similar to how CMake needs to have qrc and QML module imports in the CMakeLists
+            // and they cannot just be in the build.rs and cc_builder_whole_archive.
+            //
+            // We likely need to have qt-static-initializers linked somewhere to solve this.
+            self.cc_builder.file(&std_types_path);
+        }
+
         if cc_builder_whole_archive_files_added {
             cc_builder_whole_archive.compile("qt-static-initializers");
         }

crates/cxx-qt-lib/build.rs

@@ -232,8 +232,6 @@ fn main() {
     }
     builder.file("src/qt_types.cpp");
     println!("cargo:rerun-if-changed=src/qt_types.cpp");
-    builder.file("src/std_types.cpp");
-    println!("cargo:rerun-if-changed=src/std_types.cpp");
     println!("cargo:rerun-if-changed=src/assertion_utils.h");
 
     // Write this library's manually written C++ headers to files and add them to include paths
@@ -251,11 +249,14 @@ fn main() {
         builder.define("CXX_QT_QML_FEATURE", None);
     }
 
+    // Note, ensure our settings stay in sync across cxx-qt-build and cxx-qt-lib
+    builder.cpp(true);
     // MSVC
     builder.flag_if_supported("/std:c++17");
     builder.flag_if_supported("/Zc:__cplusplus");
     builder.flag_if_supported("/permissive-");
     // GCC + Clang
     builder.flag_if_supported("-std=c++17");
+
     builder.compile("cxx-qt-lib");
 }