IWYU: Add `--driver-mode=cl` when applicable

We already do this for `clang-tidy`.

Fixes: #16554

10 files changed, 47 insertions, 3 deletions

diff --git a/Modules/Compiler/Clang-C.cmake b/Modules/Compiler/Clang-C.cmake
index cf493d7..1b765ad 100644
--- a/Modules/Compiler/Clang-C.cmake
+++ b/Modules/Compiler/Clang-C.cmake
@@ -9,6 +9,7 @@ endif()
 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)
diff --git a/Modules/Compiler/Clang-CXX.cmake b/Modules/Compiler/Clang-CXX.cmake
index 98828e0..84b05d7 100644
--- a/Modules/Compiler/Clang-CXX.cmake
+++ b/Modules/Compiler/Clang-CXX.cmake
@@ -22,6 +22,7 @@ endif()
 
 if("x${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
   set(CMAKE_CXX_CLANG_TIDY_DRIVER_MODE "cl")
+  set(CMAKE_CXX_INCLUDE_WHAT_YOU_USE_DRIVER_MODE "cl")
   if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
       AND CMAKE_GENERATOR MATCHES "Makefiles"
       AND CMAKE_DEPFILE_FLAGS_CXX)
diff --git a/Modules/Compiler/Intel-C.cmake b/Modules/Compiler/Intel-C.cmake
index ead9069..9884b58 100644
--- a/Modules/Compiler/Intel-C.cmake
+++ b/Modules/Compiler/Intel-C.cmake
@@ -17,6 +17,7 @@ if("x${CMAKE_C_SIMULATE_ID}" 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 CMAKE_C_COMPILER_VERSION VERSION_LESS 16.0.0)
     set(CMAKE_C11_STANDARD_COMPILE_OPTION "-Qstd=c11")
diff --git a/Modules/Compiler/Intel-CXX.cmake b/Modules/Compiler/Intel-CXX.cmake
index 37f339a..7c9cca9 100644
--- a/Modules/Compiler/Intel-CXX.cmake
+++ b/Modules/Compiler/Intel-CXX.cmake
@@ -16,6 +16,7 @@ endif()
 if("x${CMAKE_CXX_SIMULATE_ID}" STREQUAL "xMSVC")
 
   set(CMAKE_CXX_CLANG_TIDY_DRIVER_MODE "cl")
+  set(CMAKE_CXX_INCLUDE_WHAT_YOU_USE_DRIVER_MODE "cl")
 
   if (NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.0.0)
     set(CMAKE_CXX20_STANDARD_COMPILE_OPTION "-Qstd=c++20")
diff --git a/Modules/Compiler/IntelLLVM-C.cmake b/Modules/Compiler/IntelLLVM-C.cmake
index d69d064..d7346f6 100644
--- a/Modules/Compiler/IntelLLVM-C.cmake
+++ b/Modules/Compiler/IntelLLVM-C.cmake
@@ -4,6 +4,7 @@ __compiler_intel_llvm(C)
 if("x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
   set(CMAKE_C_COMPILE_OPTIONS_EXPLICIT_LANGUAGE -TC)
   set(CMAKE_C_CLANG_TIDY_DRIVER_MODE "cl")
+  set(CMAKE_C_INCLUDE_WHAT_YOU_USE_DRIVER_MODE "cl")
   if((NOT DEFINED CMAKE_DEPENDS_USE_COMPILER OR CMAKE_DEPENDS_USE_COMPILER)
       AND CMAKE_GENERATOR MATCHES "Makefiles|WMake"
       AND CMAKE_DEPFILE_FLAGS_C)
diff --git a/Modules/Compiler/IntelLLVM-CXX.cmake b/Modules/Compiler/IntelLLVM-CXX.cmake
index 9799888..cae1f11 100644
--- a/Modules/Compiler/IntelLLVM-CXX.cmake
+++ b/Modules/Compiler/IntelLLVM-CXX.cmake
@@ -4,6 +4,7 @@ __compiler_intel_llvm(CXX)
 if("x${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
   set(CMAKE_CXX_COMPILE_OPTIONS_EXPLICIT_LANGUAGE -TP)
   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|WMake"
       AND CMAKE_DEPFILE_FLAGS_CXX)
diff --git a/Modules/Compiler/MSVC-C.cmake b/Modules/Compiler/MSVC-C.cmake
index 73cca36..4ba1eea 100644
--- a/Modules/Compiler/MSVC-C.cmake
+++ b/Modules/Compiler/MSVC-C.cmake
@@ -29,6 +29,7 @@ endif()
 
 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")
 
 # There are no C compiler modes so we hard-code the known compiler supported
 # features. Override the default macro for this special case.  Pretend that
diff --git a/Modules/Compiler/MSVC-CXX.cmake b/Modules/Compiler/MSVC-CXX.cmake
index 09fe851..9bb7722 100644
--- a/Modules/Compiler/MSVC-CXX.cmake
+++ b/Modules/Compiler/MSVC-CXX.cmake
@@ -4,6 +4,7 @@
 include(Compiler/CMakeCommonCompilerMacros)
 
 set(CMAKE_CXX_CLANG_TIDY_DRIVER_MODE "cl")
+set(CMAKE_CXX_INCLUDE_WHAT_YOU_USE_DRIVER_MODE "cl")
 
 if ((CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 19.0.24215.1 AND
      CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.10) OR
diff --git a/Source/cmMakefileTargetGenerator.cxx b/Source/cmMakefileTargetGenerator.cxx
index c83a7ab..70b6d27 100644
--- a/Source/cmMakefileTargetGenerator.cxx
+++ b/Source/cmMakefileTargetGenerator.cxx
@@ -999,7 +999,25 @@ void cmMakefileTargetGenerator::WriteObjectRuleFiles(
         }
         if (cmNonempty(iwyu)) {
           run_iwyu += " --iwyu=";
-          run_iwyu += this->LocalGenerator->EscapeForShell(*iwyu);
+
+          // Only add --driver-mode if it is not already specified, as adding
+          // it unconditionally might override a user-specified driver-mode
+          if (iwyu.Get()->find("--driver-mode=") == std::string::npos) {
+            cmProp p = this->Makefile->GetDefinition(
+              cmStrCat("CMAKE_", lang, "_INCLUDE_WHAT_YOU_USE_DRIVER_MODE"));
+            std::string driverMode;
+
+            if (cmNonempty(p)) {
+              driverMode = *p;
+            } else {
+              driverMode = lang == "C" ? "gcc" : "g++";
+            }
+
+            run_iwyu += this->LocalGenerator->EscapeForShell(
+              cmStrCat(*iwyu, ";--driver-mode=", driverMode));
+          } else {
+            run_iwyu += this->LocalGenerator->EscapeForShell(*iwyu);
+          }
         }
         if (cmNonempty(tidy)) {
           run_iwyu += " --tidy=";
diff --git a/Source/cmNinjaTargetGenerator.cxx b/Source/cmNinjaTargetGenerator.cxx
index 1b6b834..f1ea229 100644
--- a/Source/cmNinjaTargetGenerator.cxx
+++ b/Source/cmNinjaTargetGenerator.cxx
@@ -874,8 +874,26 @@ void cmNinjaTargetGenerator::WriteCompileRule(const std::string& lang,
         compilerLauncher.clear();
       }
       if (cmNonempty(iwyu)) {
-        run_iwyu += cmStrCat(" --iwyu=",
-                             this->GetLocalGenerator()->EscapeForShell(*iwyu));
+        run_iwyu += " --iwyu=";
+
+        // Only add --driver-mode if it is not already specified, as adding
+        // it unconditionally might override a user-specified driver-mode
+        if (iwyu.Get()->find("--driver-mode=") == std::string::npos) {
+          cmProp p = this->Makefile->GetDefinition(
+            cmStrCat("CMAKE_", lang, "_INCLUDE_WHAT_YOU_USE_DRIVER_MODE"));
+          std::string driverMode;
+
+          if (cmNonempty(p)) {
+            driverMode = *p;
+          } else {
+            driverMode = lang == "C" ? "gcc" : "g++";
+          }
+
+          run_iwyu += this->LocalGenerator->EscapeForShell(
+            cmStrCat(*iwyu, ";--driver-mode=", driverMode));
+        } else {
+          run_iwyu += this->LocalGenerator->EscapeForShell(*iwyu);
+        }
       }
       if (cmNonempty(tidy)) {
         run_iwyu += " --tidy=";