feat: lib: Serde support for QString (KDAB#944)

See also: KDAB#943

Co-authored-by: Montel Laurent <laurent.montel@kdab.com>

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `c_void` in CXX-Qt-lib for easy access to `void *`
 - `CxxQtThread` is now marked as `Sync` so that it can be used by reference
 - Add cxx-qt-lib-extras crate which contains: `QCommandLineOption`, `QCommandLineParser`, `QElapsedTimer`, `QApplication`
+- Serde support for `QString` (requires "serde" feature on cxx-qt-lib)
 
 ### Changed
 

crates/cxx-qt-lib/Cargo.toml

@@ -22,6 +22,7 @@ http = { version = "1.0", optional = true }
 rgb = { version = "0.8", optional = true }
 time = { version = "0.3.20", optional = true }
 url = { version = "2.3", optional = true }
+serde = { version = "1", features=["derive"], optional = true }
 
 [build-dependencies]
 cxx-qt-build.workspace = true
@@ -37,4 +38,5 @@ qt_gui = ["cxx-qt-lib-headers/qt_gui"]
 qt_qml = ["cxx-qt-lib-headers/qt_qml"]
 time = ["dep:time"]
 url = ["dep:url"]
+serde = ["dep:serde"]
 link_qt_object_files = ["cxx-qt-build/link_qt_object_files"]

crates/cxx-qt-lib/src/core/qstring.rs

@@ -191,10 +191,15 @@ mod ffi {
     }
 }
 
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+
 /// The QString class provides a Unicode character string.
 ///
 /// Note that QString is a UTF-16 whereas Rust strings are a UTF-8
 #[repr(C)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "serde", serde(from = "String", into = "String"))]
 pub struct QString {
     /// The layout has changed between Qt 5 and Qt 6
     ///
@@ -293,6 +298,15 @@ impl From<&String> for QString {
     }
 }
 
+impl From<String> for QString {
+    /// Constructs a QString from a Rust string
+    ///
+    /// Note that this converts from UTF-8 to UTF-16
+    fn from(str: String) -> Self {
+        ffi::qstring_init_from_rust_string(&str)
+    }
+}
+
 impl From<&QString> for String {
     /// Convert the QString to a Rust string
     ///
@@ -302,6 +316,15 @@ impl From<&QString> for String {
     }
 }
 
+impl From<QString> for String {
+    /// Convert the QString to a Rust string
+    ///
+    /// Note that this converts from UTF-16 to UTF-8
+    fn from(qstring: QString) -> Self {
+        ffi::qstring_to_rust_string(&qstring)
+    }
+}
+
 impl QString {
     /// Returns a copy of this string with the lowest numbered place marker replaced by string a, i.e., %1, %2, ..., %99.
     pub fn arg(&self, a: &QString) -> Self {

examples/qml_features/rust/Cargo.toml

@@ -16,7 +16,7 @@ crate-type = ["staticlib"]
 [dependencies]
 cxx.workspace = true
 cxx-qt.workspace = true
-cxx-qt-lib.workspace = true
+cxx-qt-lib = { workspace = true, features=["serde"] }
 serde.workspace = true
 serde_json.workspace = true
 

examples/qml_features/rust/src/serialisation.rs

@@ -10,22 +10,6 @@
 
 use serde::{Deserialize, Serialize};
 
-/// A struct representating our serialised form
-#[derive(Deserialize, Serialize)]
-pub struct DataSerde {
-    number: i32,
-    string: String,
-}
-
-impl From<&SerialisationRust> for DataSerde {
-    fn from(value: &SerialisationRust) -> DataSerde {
-        DataSerde {
-            number: value.number,
-            string: value.string.to_string(),
-        }
-    }
-}
-
 /// A CXX-Qt bridge which shows how use serde for (de)serialization of the data in a QObjects' QPROPERTY's
 #[cxx_qt::bridge(cxx_file_stem = "serialisation")]
 pub mod qobject {
@@ -63,6 +47,7 @@ use cxx_qt::CxxQtType;
 use cxx_qt_lib::QString;
 
 /// A QObject which can be serialised
+#[derive(Serialize, Deserialize)]
 pub struct SerialisationRust {
     /// The number Q_PROPERTY
     pub number: i32,
@@ -73,25 +58,14 @@ pub struct SerialisationRust {
 impl Default for SerialisationRust {
     fn default() -> Self {
         let string = r#"{"number": 4, "string": "Hello World!"}"#;
-        let data_serde: DataSerde = serde_json::from_str(string).unwrap();
-        data_serde.into()
-    }
-}
-
-impl From<DataSerde> for SerialisationRust {
-    fn from(value: DataSerde) -> Self {
-        Self {
-            number: value.number,
-            string: QString::from(&value.string),
-        }
+        serde_json::from_str(string).unwrap()
     }
 }
 
 impl qobject::Serialisation {
     /// Retrieve the JSON form of this QObject
     pub fn as_json_str(self: Pin<&mut Self>) -> QString {
-        let data_serde = DataSerde::from(self.rust());
-        match serde_json::to_string(&data_serde) {
+        match serde_json::to_string(&self.rust()) {
             Ok(data_string) => QString::from(&data_string),
             Err(err) => {
                 self.error(QString::from(&err.to_string()));
@@ -102,11 +76,11 @@ impl qobject::Serialisation {
 
     /// From a given JSON string try to load values for the Q_PROPERTYs
     // ANCHOR: book_grab_values
-    pub fn from_json_str(mut self: Pin<&mut Self>, string: &QString) {
-        match serde_json::from_str::<DataSerde>(&string.to_string()) {
+    pub fn from_json_str(mut self: Pin<&mut Self>, qstring: &QString) {
+        match serde_json::from_str::<SerialisationRust>(&qstring.to_string()) {
             Ok(data_serde) => {
                 self.as_mut().set_number(data_serde.number);
-                self.as_mut().set_string(QString::from(&data_serde.string));
+                self.as_mut().set_string(data_serde.string);
             }
             Err(err) => {
                 self.error(QString::from(&err.to_string()));