From f54117c6b1d24be6fde850099cdbe81f886ebe0f Mon Sep 17 00:00:00 2001
From: Tyler Yankee <tyler.yankee@kitware.com>
Date: Sun, 25 Oct 2026 19:31:05 -0400
Subject: [PATCH] Ninja: Evaluate generator expressions in CODEGEN outputs

Codegen is supported for Ninja Multi-Config, so CODEGEN should support
generator expressions.
---
 Help/command/add_custom_command.rst                 |  4 ++++
 Source/cmGlobalNinjaGenerator.cxx                   |  4 +++-
 Tests/RunCMake/Codegen/RunCMakeTest.cmake           | 10 ++++++++++
 Tests/RunCMake/Codegen/per-config-build-check.cmake | 11 +++++++++++
 Tests/RunCMake/Codegen/per-config.cmake             | 11 +++++++++++
 5 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 Tests/RunCMake/Codegen/per-config-build-check.cmake
 create mode 100644 Tests/RunCMake/Codegen/per-config.cmake

diff --git a/Help/command/add_custom_command.rst b/Help/command/add_custom_command.rst
index 75b66e999b..ec9e51e848 100644
--- a/Help/command/add_custom_command.rst
+++ b/Help/command/add_custom_command.rst
@@ -264,6 +264,10 @@ Generating Files
     It can only be set on the first call to ``add_custom_command(OUTPUT...)``
     for the output files.
 
+    .. versionchanged:: 4.5
+      Arguments to ``OUTPUT`` may use
+      :manual:`generator expressions <cmake-generator-expressions(7)>`.
+
   ``IMPLICIT_DEPENDS``
     Request scanning of implicit dependencies of an input file.
     The language given specifies the programming language whose
diff --git a/Source/cmGlobalNinjaGenerator.cxx b/Source/cmGlobalNinjaGenerator.cxx
index 46e5d23df8..9cc1eaae2a 100644
--- a/Source/cmGlobalNinjaGenerator.cxx
+++ b/Source/cmGlobalNinjaGenerator.cxx
@@ -23,6 +23,7 @@
 #include "cmsys/String.h"
 
 #include "cmCustomCommand.h"
+#include "cmCustomCommandGenerator.h"
 #include "cmCxxModuleMapper.h"
 #include "cmDiagnostics.h"
 #include "cmDyndepCollation.h"
@@ -1713,7 +1714,8 @@ void cmGlobalNinjaGenerator::AppendCodegenOutputs(
   for (cmSourceFile const* sf : customCommandSources) {
     cmCustomCommand const* cc = sf->GetCustomCommand();
     if (cc->GetCodegen()) {
-      std::vector<std::string> const& outputs = cc->GetOutputs();
+      cmCustomCommandGenerator ccg(*cc, config, target->GetLocalGenerator());
+      std::vector<std::string> const& outputs = ccg.GetOutputs();
       std::transform(outputs.begin(), outputs.end(), std::back_inserter(deps),
                      this->MapToNinjaPath());
     }
diff --git a/Tests/RunCMake/Codegen/RunCMakeTest.cmake b/Tests/RunCMake/Codegen/RunCMakeTest.cmake
index a159f88fb1..cec1dc7610 100644
--- a/Tests/RunCMake/Codegen/RunCMakeTest.cmake
+++ b/Tests/RunCMake/Codegen/RunCMakeTest.cmake
@@ -28,6 +28,16 @@ run_codegen("add-custom-command-depends")
 run_codegen("byproducts")
 run_codegen("add-dependencies-not-all")
 
+# Outputs that differ per configuration
+block()
+  if(RunCMake_GENERATOR_IS_MULTI_CONFIG)
+    set(RunCMake_TEST_OPTIONS "-DCMAKE_CONFIGURATION_TYPES=Debug\\;Release")
+  else()
+    set(RunCMake_TEST_OPTIONS -DCMAKE_BUILD_TYPE=Debug)
+  endif()
+  run_codegen("per-config")
+endblock()
+
 # Error handling
 run_cmake("implicit-depends")
 run_cmake("implicit-depends-append-codegen")
diff --git a/Tests/RunCMake/Codegen/per-config-build-check.cmake b/Tests/RunCMake/Codegen/per-config-build-check.cmake
new file mode 100644
index 0000000000..6989e0d1a9
--- /dev/null
+++ b/Tests/RunCMake/Codegen/per-config-build-check.cmake
@@ -0,0 +1,11 @@
+set(filename "${RunCMake_TEST_BINARY_DIR}/Debug/generated.h")
+if (NOT EXISTS "${filename}")
+  set(RunCMake_TEST_FAILED "expected file NOT created:\n ${filename}")
+  return()
+endif()
+
+set(filename "${RunCMake_TEST_BINARY_DIR}/Release/generated.h")
+if (EXISTS "${filename}")
+  set(RunCMake_TEST_FAILED "unexpected file created:\n ${filename}")
+  return()
+endif()
diff --git a/Tests/RunCMake/Codegen/per-config.cmake b/Tests/RunCMake/Codegen/per-config.cmake
new file mode 100644
index 0000000000..1b59731d42
--- /dev/null
+++ b/Tests/RunCMake/Codegen/per-config.cmake
@@ -0,0 +1,11 @@
+add_custom_command(
+  OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>/generated.h
+  COMMAND ${CMAKE_COMMAND} -E copy
+    ${CMAKE_CURRENT_SOURCE_DIR}/generated.h.in
+    ${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>/generated.h
+  CODEGEN
+)
+
+add_custom_target(h_creator ALL
+  DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>/generated.h
+)