C++: Add a mechanism to #define features that are enabled (#3103)

api/cpp/CMakeLists.txt

@@ -221,10 +221,6 @@ if((SLINT_FEATURE_RENDERER_WINIT_SKIA OR SLINT_FEATURE_RENDERER_WINIT_SKIA_OPENG
     endif()
 endif()
 
-if(SLINT_FEATURE_EXPERIMENTAL)
-    target_compile_definitions(Slint INTERFACE SLINT_FEATURE_EXPERIMENTAL)
-endif()
-
 file(GLOB api_headers RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}/include/"
     "${CMAKE_CURRENT_SOURCE_DIR}/include/*.h")
 

api/cpp/build.rs

@@ -1,6 +1,7 @@
 // Copyright © SixtyFPS GmbH <info@slint.dev>
 // SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-1.1 OR LicenseRef-Slint-commercial
 
+use crate::cbindgen::EnabledFeatures;
 use std::path::Path;
 mod cbindgen;
 
@@ -20,8 +21,13 @@ fn main() -> Result<(), anyhow::Error> {
 
     println!("cargo:GENERATED_INCLUDE_DIR={}", output_dir.display());
 
-    let include_interpreter = std::env::var("CARGO_FEATURE_SLINT_INTERPRETER").is_ok();
-    let dependencies = cbindgen::gen_all(&root_dir, &output_dir, include_interpreter)?;
+    let enabled_features = EnabledFeatures {
+        interpreter: std::env::var("CARGO_FEATURE_SLINT_INTERPRETER").is_ok(),
+        experimental: std::env::var("CARGO_FEATURE_SLINT_INTERPRETER").is_ok(),
+        backend_qt: std::env::var("CARGO_FEATURE_BACKEND_QT").is_ok(),
+    };
+
+    let dependencies = cbindgen::gen_all(&root_dir, &output_dir, enabled_features)?;
     for path in dependencies {
         println!("cargo:rerun-if-changed={}", path.display());
     }

api/cpp/cbindgen.rs

@@ -110,6 +110,7 @@ fn gen_corelib(
     root_dir: &Path,
     include_dir: &Path,
     dependencies: &mut Vec<PathBuf>,
+    enabled_features: EnabledFeatures,
 ) -> anyhow::Result<()> {
     let mut config = default_config();
 
@@ -448,10 +449,13 @@ fn gen_corelib(
 /// This macro expands to the string representation of the version of Slint you're developing against.
 /// For example if you're using version 1.5.2, this macro will expand to "1.5.2".
 #define SLINT_VERSION_STRING "{x}.{y}.{z}"
+
+{features}
 "#,
             x = env!("CARGO_PKG_VERSION_MAJOR"),
             y = env!("CARGO_PKG_VERSION_MINOR"),
             z = env!("CARGO_PKG_VERSION_PATCH"),
+            features = enabled_features.defines()
         ))
         .generate()
         .context("Unable to generate bindings for slint_generated_public.h")?
@@ -688,6 +692,30 @@ fn gen_interpreter(
     Ok(())
 }
 
+#[derive(Clone, Copy)]
+pub struct EnabledFeatures {
+    pub interpreter: bool,
+    pub experimental: bool,
+    pub backend_qt: bool,
+}
+
+impl EnabledFeatures {
+    /// Generate the `#define`
+    fn defines(self) -> String {
+        let mut defines = String::new();
+        if self.interpreter {
+            defines += "#define SLINT_FEATURE_INTERPRETER\n";
+        }
+        if self.experimental {
+            defines += "#define SLINT_FEATURE_EXPERIMENTAL\n";
+        }
+        if self.backend_qt {
+            defines += "#define SLINT_FEATURE_BACKEND_QT\n";
+        }
+        defines
+    }
+}
+
 /// Generate the headers.
 /// `root_dir` is the root directory of the slint git repo
 /// `include_dir` is the output directory
@@ -696,16 +724,16 @@ fn gen_interpreter(
 pub fn gen_all(
     root_dir: &Path,
     include_dir: &Path,
-    include_interpreter: bool,
+    enabled_features: EnabledFeatures,
 ) -> anyhow::Result<Vec<PathBuf>> {
     proc_macro2::fallback::force(); // avoid a abort if panic=abort is set
     std::fs::create_dir_all(include_dir).context("Could not create the include directory")?;
     let mut deps = Vec::new();
     enums(&include_dir.join("slint_enums_internal.h"))?;
-    gen_corelib(root_dir, include_dir, &mut deps)?;
+    gen_corelib(root_dir, include_dir, &mut deps, enabled_features)?;
     gen_backend_qt(root_dir, include_dir, &mut deps)?;
     gen_backend(root_dir, include_dir, &mut deps)?;
-    if include_interpreter {
+    if enabled_features.interpreter {
         gen_interpreter(root_dir, include_dir, &mut deps)?;
     }
     Ok(deps)

api/cpp/include/slint_interpreter.h

@@ -5,17 +5,17 @@
 
 #include "slint.h"
 
-#include "slint_interpreter_internal.h"
+#ifndef SLINT_FEATURE_INTERPRETER
+#    warning "slint_interpreter.h API only available when SLINT_FEATURE_INTERPRETER is activated"
+#else
 
-#include <optional>
+#    include "slint_interpreter_internal.h"
 
-#if !defined(DOXYGEN)
-#    define SLINT_QT_INTEGRATION // In the future, should be defined by cmake only if this is
-                                 // enabled
-#endif
-#ifdef SLINT_QT_INTEGRATION
+#    include <optional>
+
+#    ifdef SLINT_FEATURE_BACKEND_QT
 class QWidget;
-#endif
+#    endif
 
 namespace slint::cbindgen_private {
 //  This has to stay opaque, but VRc don't compile if it is just forward declared
@@ -96,7 +96,7 @@ struct Struct
     /// advanced until it equals \a end.
     template<typename InputIterator
 // Doxygen doesn't understand this template wizardry
-#if !defined(DOXYGEN)
+#    if !defined(DOXYGEN)
              ,
              typename std::enable_if_t<
                      std::is_convertible<decltype(std::get<0>(*std::declval<InputIterator>())),
@@ -105,7 +105,7 @@ struct Struct
                                             Value>::value
 
                      > * = nullptr
-#endif
+#    endif
              >
     Struct(InputIterator it, InputIterator end) : Struct()
     {
@@ -576,7 +576,7 @@ class ComponentInstance : vtable::Dyn
         cbindgen_private::slint_run_event_loop();
         hide();
     }
-#if defined(SLINT_QT_INTEGRATION) || defined(DOXYGEN)
+#    if defined(SLINT_FEATURE_BACKEND_QT) || defined(DOXYGEN)
     /// Return a QWidget for this instance.
     /// This function is only available if the qt graphical backend was compiled in, and
     /// it may return nullptr if the Qt backend is not used at runtime.
@@ -588,7 +588,7 @@ class ComponentInstance : vtable::Dyn
                 reinterpret_cast<const cbindgen_private::WindowAdapterRc *>(win_ptr)));
         return wid;
     }
-#endif
+#    endif
 
     /// Set the value for a public property of this component
     ///
@@ -1029,3 +1029,5 @@ inline void send_keyboard_string_sequence(const slint::interpreter::ComponentIns
             &str, reinterpret_cast<const cbindgen_private::WindowAdapterRc *>(win_ptr));
 }
 }
+
+#endif

api/cpp/include/slint_platform.h

@@ -3,11 +3,12 @@
 
 #pragma once
 
+#include "slint.h"
+
 #ifndef SLINT_FEATURE_EXPERIMENTAL
 #    warning "slint_platform.h API only available when SLINT_FEATURE_EXPERIMENTAL is activated"
 #else
 
-#    include "slint.h"
 #    include <utility>
 
 struct xcb_connection_t;

xtask/src/cppdocs.rs

@@ -87,8 +87,9 @@ pub fn generate(show_warnings: bool) -> Result<(), Box<dyn std::error::Error>> {
     )?;
 
     let generated_headers_dir = docs_build_dir.join("generated_include");
-    let include_interpreter = true;
-    cbindgen::gen_all(&root, &generated_headers_dir, include_interpreter)?;
+    let enabled_features =
+        cbindgen::EnabledFeatures { interpreter: true, experimental: false, backend_qt: false };
+    cbindgen::gen_all(&root, &generated_headers_dir, enabled_features)?;
 
     let pip_env = vec![(OsString::from("PIPENV_PIPFILE"), docs_source_dir.join("docs/Pipfile"))];