clang-cl: use gcc depfiles over /showIncludes

This enables `#embed` dependencies when using `clang-cl`.

Fixes: #27594

Modules/Compiler/Clang-C.cmake

@@ -5,11 +5,6 @@ if("x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
   set(CMAKE_C_COMPILE_OPTIONS_EXPLICIT_LANGUAGE -TC)
   set(CMAKE_C_CLANG_TIDY_DRIVER_MODE "cl")
   set(CMAKE_C_INCLUDE_WHAT_YOU_USE_DRIVER_MODE "cl")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_C)
-    set(CMAKE_C_DEPENDS_USE_COMPILER TRUE)
-  endif()
 elseif("x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xGNU")
   set(CMAKE_C_COMPILE_OPTIONS_EXPLICIT_LANGUAGE -x c)
   if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)

Modules/Compiler/Clang-CXX.cmake

@@ -18,11 +18,6 @@ endif()
 if("x${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
   set(CMAKE_CXX_CLANG_TIDY_DRIVER_MODE "cl")
   set(CMAKE_CXX_INCLUDE_WHAT_YOU_USE_DRIVER_MODE "cl")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles"
-      AND CMAKE_DEPFILE_FLAGS_CXX)
-    set(CMAKE_CXX_DEPENDS_USE_COMPILER TRUE)
-  endif()
 endif()
 
 if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 16.0)

Modules/Platform/Windows-Clang-C.cmake

@@ -1,18 +1,10 @@
 include(Platform/Windows-Clang)
 __windows_compiler_clang(C)
 
-if("x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_C)
-    set(CMAKE_C_DEPENDS_USE_COMPILER TRUE)
-  endif()
-elseif("x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xGNU")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_C)
-    # dependencies are computed by the compiler itself
-    set(CMAKE_C_DEPFILE_FORMAT gcc)
-    set(CMAKE_C_DEPENDS_USE_COMPILER TRUE)
-  endif()
+if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
+    AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
+    AND CMAKE_DEPFILE_FLAGS_C)
+  # dependencies are computed by the compiler itself
+  set(CMAKE_C_DEPFILE_FORMAT gcc)
+  set(CMAKE_C_DEPENDS_USE_COMPILER TRUE)
 endif()

Modules/Platform/Windows-Clang-CXX.cmake

@@ -2,18 +2,10 @@ include(Platform/Windows-Clang)
 set(_COMPILE_CXX_MSVC " -TP")
 __windows_compiler_clang(CXX)
 
-if("x${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_CXX)
-    set(CMAKE_CXX_DEPENDS_USE_COMPILER TRUE)
-  endif()
-elseif("x${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xGNU")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_CXX)
-    # dependencies are computed by the compiler itself
-    set(CMAKE_CXX_DEPFILE_FORMAT gcc)
-    set(CMAKE_CXX_DEPENDS_USE_COMPILER TRUE)
-  endif()
+if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
+    AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
+    AND CMAKE_DEPFILE_FLAGS_CXX)
+  # dependencies are computed by the compiler itself
+  set(CMAKE_CXX_DEPFILE_FORMAT gcc)
+  set(CMAKE_CXX_DEPENDS_USE_COMPILER TRUE)
 endif()

Modules/Platform/Windows-Clang-HIP.cmake

@@ -2,18 +2,10 @@ include(Platform/Windows-Clang)
 set(_COMPILE_HIP_MSVC " -x hip")
 __windows_compiler_clang(HIP)
 
-if("x${CMAKE_HIP_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_HIP)
-    set(CMAKE_HIP_DEPENDS_USE_COMPILER TRUE)
-  endif()
-elseif("x${CMAKE_HIP_COMPILER_FRONTEND_VARIANT}" STREQUAL "xGNU")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_HIP)
-    # dependencies are computed by the compiler itself
-    set(CMAKE_HIP_DEPFILE_FORMAT gcc)
-    set(CMAKE_HIP_DEPENDS_USE_COMPILER TRUE)
-  endif()
+if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
+    AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
+    AND CMAKE_DEPFILE_FLAGS_HIP)
+  # dependencies are computed by the compiler itself
+  set(CMAKE_HIP_DEPFILE_FORMAT gcc)
+  set(CMAKE_HIP_DEPENDS_USE_COMPILER TRUE)
 endif()

Modules/Platform/Windows-Clang-OBJC.cmake

@@ -1,18 +1,10 @@
 include(Platform/Windows-Clang)
 __windows_compiler_clang(OBJC)
 
-if("x${CMAKE_OBJC_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_OBJC)
-    set(CMAKE_OBJC_DEPENDS_USE_COMPILER TRUE)
-  endif()
-elseif("x${CMAKE_OBJC_COMPILER_FRONTEND_VARIANT}" STREQUAL "xGNU")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_OBJC)
-    # dependencies are computed by the compiler itself
-    set(CMAKE_OBJC_DEPFILE_FORMAT gcc)
-    set(CMAKE_OBJC_DEPENDS_USE_COMPILER TRUE)
-  endif()
+if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
+    AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
+    AND CMAKE_DEPFILE_FLAGS_OBJC)
+  # dependencies are computed by the compiler itself
+  set(CMAKE_OBJC_DEPFILE_FORMAT gcc)
+  set(CMAKE_OBJC_DEPENDS_USE_COMPILER TRUE)
 endif()

Modules/Platform/Windows-Clang-OBJCXX.cmake

@@ -1,18 +1,10 @@
 include(Platform/Windows-Clang)
 __windows_compiler_clang(OBJCXX)
 
-if("x${CMAKE_OBJCXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_OBJCXX)
-    set(CMAKE_OBJCXX_DEPENDS_USE_COMPILER TRUE)
-  endif()
-elseif("x${CMAKE_OBJCXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xGNU")
-  if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
-      AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
-      AND CMAKE_DEPFILE_FLAGS_OBJCXX)
-    # dependencies are computed by the compiler itself
-    set(CMAKE_OBJCXX_DEPFILE_FORMAT gcc)
-    set(CMAKE_OBJCXX_DEPENDS_USE_COMPILER TRUE)
-  endif()
+if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
+    AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
+    AND CMAKE_DEPFILE_FLAGS_OBJCXX)
+  # dependencies are computed by the compiler itself
+  set(CMAKE_OBJCXX_DEPFILE_FORMAT gcc)
+  set(CMAKE_OBJCXX_DEPENDS_USE_COMPILER TRUE)
 endif()

Modules/Platform/Windows-Clang.cmake

@@ -233,6 +233,11 @@ if("x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC"
     macro(__windows_compiler_clang_base lang)
       set(_COMPILE_${lang} "${_COMPILE_${lang}_MSVC}")
       __windows_compiler_msvc(${lang})
+
+      # Prefer clang-cl's gcc-style depfile over cl-style /showIncludes
+      set(CMAKE_DEPFILE_FLAGS_${lang} "-clang:-MD -clang:-MT<DEP_TARGET> -clang:-MF<DEP_FILE>")
+      unset(CMAKE_${lang}_DEPFILE_FORMAT)
+
       unset(CMAKE_${lang}_COMPILE_OPTIONS_MSVC_DEBUG_INFORMATION_FORMAT_EditAndContinue) # -ZI not supported by Clang
       set(CMAKE_${lang}_COMPILE_OPTIONS_WARNING_AS_ERROR "-WX")
       set(CMAKE_INCLUDE_SYSTEM_FLAG_${lang} "-imsvc")