Emscripten: Add platform modules

Issue: #18423

Help/manual/cmake-toolchains.7.rst

@@ -704,3 +704,22 @@ the next rules to make device + simulator configuration work:
 
 - Use :command:`find_package` only for libraries installed with
   :variable:`CMAKE_IOS_INSTALL_COMBINED` feature
+
+.. _`Cross Compiling for Emscripten`:
+
+Cross Compiling for Emscripten
+------------------------------
+
+.. versionadded:: 4.2
+
+A toolchain file may configure cross-compiling for `Emscripten`_ by
+setting the :variable:`CMAKE_SYSTEM_NAME` variable to ``Emscripten``.
+For example, a toolchain file might contain:
+
+.. code-block:: cmake
+
+  set(CMAKE_SYSTEM_NAME Emscripten)
+  set(CMAKE_C_COMPILER /path/to/emcc)
+  set(CMAKE_CXX_COMPILER /path/to/em++)
+
+.. _`Emscripten`: https://emscripten.org/

Help/release/dev/emscripten-platform.rst

@@ -0,0 +1,5 @@
+emscripten-platform
+-------------------
+
+* CMake now supports :ref:`Cross Compiling for Emscripten` with simple
+  toolchain files.

Modules/CMakeFindBinUtils.cmake

@@ -219,6 +219,11 @@ else()
     list(PREPEND _CMAKE_LINKER_NAMES "armlink")
   endif()
 
+  if(EMSCRIPTEN)
+    list(PREPEND _CMAKE_AR_NAMES "emar")
+    list(PREPEND _CMAKE_RANLIB_NAMES "emranlib")
+  endif()
+
   list(APPEND _CMAKE_TOOL_VARS AR RANLIB STRIP LINKER NM OBJDUMP OBJCOPY READELF DLLTOOL ADDR2LINE TAPI)
 endif()
 

Modules/Platform/Emscripten-Clang-C.cmake

@@ -0,0 +1,3 @@
+include(Platform/Emscripten-Clang)
+
+__emscripten_clang(C)

Modules/Platform/Emscripten-Clang-CXX.cmake

@@ -0,0 +1,3 @@
+include(Platform/Emscripten-Clang)
+
+__emscripten_clang(CXX)

Modules/Platform/Emscripten-Clang.cmake

@@ -0,0 +1,17 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file LICENSE.rst or https://cmake.org/licensing for details.
+
+include_guard()
+
+macro(__emscripten_clang lang)
+  set(CMAKE_SHARED_LIBRARY_SONAME_${lang}_FLAG "-Wl,-soname,")
+  set(CMAKE_SHARED_LIBRARY_CREATE_${lang}_FLAGS "-sSIDE_MODULE")
+
+  set(CMAKE_${lang}_USE_RESPONSE_FILE_FOR_LIBRARIES 1)
+  set(CMAKE_${lang}_USE_RESPONSE_FILE_FOR_OBJECTS 1)
+  set(CMAKE_${lang}_USE_RESPONSE_FILE_FOR_INCLUDES 1)
+  set(CMAKE_${lang}_COMPILE_OBJECT
+    "<CMAKE_${lang}_COMPILER> -c <SOURCE> <DEFINES> <INCLUDES> <FLAGS> -o <OBJECT> -fPIC")
+  set(CMAKE_${lang}_LINK_EXECUTABLE
+    "<CMAKE_${lang}_COMPILER> <FLAGS> <CMAKE_${lang}_LINK_FLAGS> <LINK_FLAGS> <OBJECTS> -o <TARGET> <LINK_LIBRARIES> -sMAIN_MODULE")
+endmacro()

Modules/Platform/Emscripten-Initialize.cmake

@@ -0,0 +1,2 @@
+set(EMSCRIPTEN 1)
+set(UNIX 1)

Modules/Platform/Emscripten.cmake

@@ -0,0 +1,6 @@
+set(CMAKE_SHARED_LIBRARY_LINK_C_WITH_RUNTIME_PATH ON)
+
+set(CMAKE_SHARED_LIBRARY_SUFFIX ".wasm")
+set(CMAKE_EXECUTABLE_SUFFIX ".js")
+
+set(CMAKE_DL_LIBS "")

Modules/Platform/Linker/Emscripten-C.cmake

@@ -0,0 +1,4 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file LICENSE.rst or https://cmake.org/licensing for details.
+
+include(Platform/Linker/Emscripten-LLD-C)

Modules/Platform/Linker/Emscripten-CXX.cmake

@@ -0,0 +1,4 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file LICENSE.rst or https://cmake.org/licensing for details.
+
+include(Platform/Linker/Emscripten-LLD-CXX)

Modules/Platform/Linker/Emscripten-LLD-C.cmake

@@ -0,0 +1,6 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file LICENSE.rst or https://cmake.org/licensing for details.
+
+include(Platform/Linker/Emscripten-LLD)
+
+__emscripten_linker_lld(C)

Modules/Platform/Linker/Emscripten-LLD-CXX.cmake

@@ -0,0 +1,6 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file LICENSE.rst or https://cmake.org/licensing for details.
+
+include(Platform/Linker/Emscripten-LLD)
+
+__emscripten_linker_lld(CXX)

Modules/Platform/Linker/Emscripten-LLD.cmake

@@ -0,0 +1,11 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file LICENSE.rst or https://cmake.org/licensing for details.
+
+# This module is shared by multiple languages; use include blocker.
+include_guard()
+
+macro(__emscripten_linker_lld lang)
+  set(CMAKE_${lang}_LINK_LIBRARY_USING_WHOLE_ARCHIVE "-Wl,--whole-archive" "<LINK_ITEM>" "-Wl,--no-whole-archive")
+  set(CMAKE_${lang}_LINK_LIBRARY_USING_WHOLE_ARCHIVE_SUPPORTED TRUE)
+  set(CMAKE_${lang}_LINK_LIBRARY_WHOLE_ARCHIVE_ATTRIBUTES LIBRARY_TYPE=STATIC DEDUPLICATION=YES OVERRIDE=DEFAULT)
+endmacro()

Source/cmCoreTryCompile.cxx

@@ -1386,6 +1386,14 @@ void cmCoreTryCompile::FindOutputFile(std::string const& targetName)
     return;
   }
 
+  if (cmHasLiteralSuffix(outputFileLocation, ".js")) {
+    std::string wasmOutputLocation = cmStrCat(
+      outputFileLocation.substr(0, outputFileLocation.length() - 3), ".wasm");
+    if (cmSystemTools::FileExists(wasmOutputLocation)) {
+      outputFileLocation = wasmOutputLocation;
+    }
+  }
+
   this->OutputFile = cmSystemTools::CollapseFullPath(outputFileLocation);
 }