plugin: use --dynamic-list to add qt entry symbols past rust's version script

plugin/build.rs

@@ -1,21 +1,27 @@
 use cxx_qt_build::{CxxQtBuilder, PluginType, QmlModule};
 
 fn main() {
-    // Two separate problems to defeat in the cdylib link:
+    // Two separate problems to defeat in the cdylib link for cxx-qt's QML plugin
+    // entry points (qt_plugin_instance / qt_plugin_query_metadata_v2):
     // 1. cc-rs uses -ffunction-sections, Rust's cdylib runs --gc-sections, and
-    //    nothing internal references qt_plugin_instance / qt_plugin_query_metadata_v2
+    //    nothing internal references those symbols (moc emits them as dlsym
-    //    (moc emits them as dlsym entry points for Qt's plugin loader, not for
+    //    entry points), so the linker drops them entirely. --undefined=<sym>
-    //    in-binary calls), so the linker drops them entirely. --undefined=<sym>
     //    anchors them past --gc-sections.
-    // 2. Even once present, Rust's cdylib link hides C++ static-archive symbols by
+    // 2. Rust's cdylib link passes an explicit --version-script that exports
-    //    default - they end up as local (lowercase t in nm), invisible to dlsym.
+    //    only Rust-public symbols - everything else, including our anchored C++
-    //    --export-dynamic-symbol=<sym> doesn't help: that flag only applies to
+    //    plugin symbols, is hidden as local. Neither --export-dynamic nor
-    //    -shared=no (executables). For shared libraries, bare --export-dynamic
+    //    --export-dynamic-symbol overrides an explicit version script. The fix
-    //    exports all global symbols and overrides the hide-by-default.
+    //    is --dynamic-list=<file>, which is additive: it appends entries to the
+    //    dynamic symtab without fighting the version script's hides.
     for sym in ["qt_plugin_instance", "qt_plugin_query_metadata_v2"] {
         println!("cargo:rustc-link-arg=-Wl,--undefined={sym}");
     }
-    println!("cargo:rustc-link-arg=-Wl,--export-dynamic");
+    let dynlist = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("qt_plugin_exports.txt");
+    println!("cargo:rerun-if-changed={}", dynlist.display());
+    println!(
+        "cargo:rustc-link-arg=-Wl,--dynamic-list={}",
+        dynlist.display()
+    );
 
     // Crane's deps-only build stubs out lib.rs and removes our bridge sources to
     // build a dummy crate that only compiles dependencies. Skip cxx-qt codegen in

plugin/qt_plugin_exports.txt

@@ -0,0 +1,4 @@
+{
+    qt_plugin_instance;
+    qt_plugin_query_metadata_v2;
+};