CMP0132: Don't set compiler environment variables on first run

When running CMake for the first time in a build tree, for some
generators CMake would set compiler environment variables
like CC, CXX, etc. when the corresponding language is enabled.
That behavior was never documented and can result in different
behavior between the first and subsequent runs. Add a policy
to no longer set those environment variables.

Fixes: #21378

9 files changed, 34 insertions, 0 deletions

diff --git a/Tests/RunCMake/CMP0132/CMP0132-Common.cmake b/Tests/RunCMake/CMP0132/CMP0132-Common.cmake
new file mode 100644
index 0000000..796f61c
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/CMP0132-Common.cmake
@@ -0,0 +1,15 @@
+if(NOT "$ENV{CC}" STREQUAL "")
+  message(STATUS "Test environment already sets CC, test being SKIPPED")
+  return()
+elseif(CMAKE_GENERATOR MATCHES "Xcode|Visual Studio")
+  message(STATUS "This generator never sets CC, test being SKIPPED")
+  return()
+endif()
+
+enable_language(C)
+
+if("$ENV{CC}" STREQUAL "")
+  message(STATUS "CC was left unset")
+else()
+  message(STATUS "CC was set to $ENV{CC}")
+endif()
diff --git a/Tests/RunCMake/CMP0132/CMP0132-NEW-stdout.txt b/Tests/RunCMake/CMP0132/CMP0132-NEW-stdout.txt
new file mode 100644
index 0000000..8056c2c
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/CMP0132-NEW-stdout.txt
@@ -0,0 +1 @@
+SKIPPED|CC was left unset
diff --git a/Tests/RunCMake/CMP0132/CMP0132-NEW.cmake b/Tests/RunCMake/CMP0132/CMP0132-NEW.cmake
new file mode 100644
index 0000000..fabb419
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/CMP0132-NEW.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0132 NEW)
+include(CMP0132-Common.cmake)
diff --git a/Tests/RunCMake/CMP0132/CMP0132-OLD-stdout.txt b/Tests/RunCMake/CMP0132/CMP0132-OLD-stdout.txt
new file mode 100644
index 0000000..c131428
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/CMP0132-OLD-stdout.txt
@@ -0,0 +1 @@
+SKIPPED|CC was set
diff --git a/Tests/RunCMake/CMP0132/CMP0132-OLD.cmake b/Tests/RunCMake/CMP0132/CMP0132-OLD.cmake
new file mode 100644
index 0000000..aae4f2a
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/CMP0132-OLD.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0132 OLD)
+include(CMP0132-Common.cmake)
diff --git a/Tests/RunCMake/CMP0132/CMP0132-WARN-stdout.txt b/Tests/RunCMake/CMP0132/CMP0132-WARN-stdout.txt
new file mode 100644
index 0000000..c131428
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/CMP0132-WARN-stdout.txt
@@ -0,0 +1 @@
+SKIPPED|CC was set
diff --git a/Tests/RunCMake/CMP0132/CMP0132-WARN.cmake b/Tests/RunCMake/CMP0132/CMP0132-WARN.cmake
new file mode 100644
index 0000000..c07e5db
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/CMP0132-WARN.cmake
@@ -0,0 +1,2 @@
+
+include(CMP0132-Common.cmake)
diff --git a/Tests/RunCMake/CMP0132/CMakeLists.txt b/Tests/RunCMake/CMP0132/CMakeLists.txt
new file mode 100644
index 0000000..5ff8d3e
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/CMakeLists.txt
@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.23)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)
diff --git a/Tests/RunCMake/CMP0132/RunCMakeTest.cmake b/Tests/RunCMake/CMP0132/RunCMakeTest.cmake
new file mode 100644
index 0000000..db599ce
--- /dev/null
+++ b/Tests/RunCMake/CMP0132/RunCMakeTest.cmake
@@ -0,0 +1,7 @@
+include(RunCMake)
+
+if(NOT CMAKE_GENERATOR_NO_COMPILER_ENV)
+  run_cmake(CMP0132-WARN)
+  run_cmake(CMP0132-OLD)
+  run_cmake(CMP0132-NEW)
+endif()