Merge baa5973128 into 994915dbb9

* Add the umbrella module ftxui to the cmake module build.

* Update cpp20 modules documentation.

cmake/ftxui_modules.cmake

@@ -6,6 +6,7 @@ add_library(ftxui-modules)
 
 target_sources(ftxui-modules
   PUBLIC FILE_SET CXX_MODULES FILES
+  src/ftxui/ftxui.cppm
   src/ftxui/component.cppm
   src/ftxui/component/animation.cppm
   src/ftxui/component/captured_mouse.cppm

doc/cpp20-modules.md

@@ -12,8 +12,24 @@ FTXUI experimentally supports
 compilation times and improve code organization. Each header has a
 corresponding module.
 
-**Example with CMake and Ninja**
+Use the FTXUI_BUILD_MODULES option to build the FTXUI project itself to provide C++ 20 modules,
+for example with CMake and Ninja:
 
+```sh
+cmake \
+    -DCMAKE_GENERATOR=Ninja \
+    -DFTXUI_BUILD_MODULES=ON \
+    ..
+
+ninja
+```
+
+> [!NOTE]
+> To use modules, you need a C++20 compatible compiler, CMake version 3.20 or
+> higher, and use a compatible generator like Ninja. Note that Makefile
+> generators **do not support modules**.
+
+Then, in your own code you can consume the modules and code as normal:
 
 ```cpp
 import ftxui;
@@ -26,23 +42,30 @@ int main() {
 }
 ```
 
-```sh
+Note, the `ftxui` convenience module which simply pulls together all the modules:
-cmake \
-    -DCMAKE_GENERATOR=Ninja \
-    -DFTXUI_BUILD_MODULES=ON \
-    ..
 
-ninja
+```cpp
+export import ftxui.component;
+export import ftxui.dom;
+export import ftxui.screen;
+export import ftxui.util;
+```
+You can instead import only the module(s) you need if desired.
+
+To properly find and link the modules with CMake, use `target_link_libraries` to get the right
+compiler, linker, etc. flags.
+
+```cmake
+target_link_libraries(my_executable
+    #...whatever...
+    PRIVATE ftxui::modules
+)
 ```
-> [!NOTE]
-> To use modules, you need a C++20 compatible compiler, CMake version 3.20 or
-> higher, and use a compatible generator like Ninja. Note that Makefile
-> generators **do not support modules**.
 
 ### Module list
 
 The modules directly reference the corresponding header, or a group of related
-headers to provide a more convenient interface. The following modules 
+headers to provide a more convenient interface. The following modules
 are available:
 
 - `ftxui`

src/ftxui/screen/terminal.cpp

@@ -48,25 +48,38 @@ Dimensions& FallbackSize() {
   return g_fallback_size;
 }
 
-const char* Safe(const char* c) {
-  return (c != nullptr) ? c : "";
-}
-
 bool Contains(const std::string& s, const char* key) {
   return s.find(key) != std::string::npos;
 }
 
+// https://github.com/gabime/spdlog/blob/885b5473e291833b148eeac3b7ce227e582cd88b/include/spdlog/details/os-inl.h#L566
+std::string getenv_safe(const char *field) {
+#if defined(_MSC_VER)
+#if defined(__cplusplus_winrt)
+  return std::string{};  // not supported under uwp
+#else
+  size_t len = 0;
+  char buf[1024];
+  bool ok = ::getenv_s(&len, buf, sizeof(buf), field) == 0;
+  return ok ? buf : std::string{};
+#endif
+#else  // revert to getenv
+  char *buf = ::getenv(field); // NOLINT(*-mt-unsafe)
+  return buf ? buf : std::string{};
+#endif
+}
+
 Terminal::Color ComputeColorSupport() {
 #if defined(__EMSCRIPTEN__)
   return Terminal::Color::TrueColor;
 #endif
 
-  std::string COLORTERM = Safe(std::getenv("COLORTERM"));  // NOLINT
+  std::string COLORTERM = getenv_safe("COLORTERM");
   if (Contains(COLORTERM, "24bit") || Contains(COLORTERM, "truecolor")) {
     return Terminal::Color::TrueColor;
   }
 
-  std::string TERM = Safe(std::getenv("TERM"));  // NOLINT
+  std::string TERM = getenv_safe("TERM");
   if (Contains(COLORTERM, "256") || Contains(TERM, "256")) {
     return Terminal::Color::Palette256;
   }