Compile with explicit language flag when source LANGUAGE property is set

This change was originally made by commit 74b1c9fc8e (Explicitly specify
language flag when source LANGUAGE property is set, 2020-06-01,
v3.19.0-rc1~722^2), but it was reverted by commit 30aa715fac (Revert
"specify language flag when source LANGUAGE property is set",
2020-11-19) to restore compatibility with pre-3.19 behavior.

Implement the change again, but add policy CMP0119 to make this change
while preserving compatibility with existing projects.

Note that the `Compiler/{Clang,Intel,MSVC}-CXX` modules do not need to
specify `-TP` for their MSVC-like variants because we already use the
flag in `CMAKE_CXX_COMPILE_OBJECT`.  Similarly for `Compiler/XL-CXX`
and `Platform/Windows-Embarcadero`.

Note also that this does not seem possible to implement for XL C.
Even with `-qsourcetype=c`, `xlc` complains about an unknown suffix:
`1501-218 (W) file /.../AltExtC.zzz contains an incorrect file suffix`.
It returns non-zero even with `-qsuppress=1501-218`.

Co-Author: Robert Maynard <robert.maynard@kitware.com>
Fixes: #14516, #20716

12 files changed, 45 insertions, 0 deletions

diff --git a/Tests/RunCMake/CMP0119/AltExtC.zzz b/Tests/RunCMake/CMP0119/AltExtC.zzz
new file mode 100644
index 0000000..5b240eb
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/AltExtC.zzz
@@ -0,0 +1,4 @@
+int main(void) {
+  int class = 0;
+  return class;
+}
diff --git a/Tests/RunCMake/CMP0119/AltExtCXX.zzz b/Tests/RunCMake/CMP0119/AltExtCXX.zzz
new file mode 100644
index 0000000..3c521ed
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/AltExtCXX.zzz
@@ -0,0 +1,3 @@
+int main() {
+  return static_cast<int>(0);
+}
diff --git a/Tests/RunCMake/CMP0119/CMP0119-Common.cmake b/Tests/RunCMake/CMP0119/CMP0119-Common.cmake
new file mode 100644
index 0000000..f45895b
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMP0119-Common.cmake
@@ -0,0 +1,4 @@
+enable_language(C)
+
+add_executable(AltExtC AltExtC.zzz)
+set_property(SOURCE AltExtC.zzz PROPERTY LANGUAGE C)
diff --git a/Tests/RunCMake/CMP0119/CMP0119-NEW.cmake b/Tests/RunCMake/CMP0119/CMP0119-NEW.cmake
new file mode 100644
index 0000000..df0ed48
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMP0119-NEW.cmake
@@ -0,0 +1,6 @@
+cmake_policy(SET CMP0119 NEW)
+include(CMP0119-Common.cmake)
+
+enable_language(CXX)
+add_executable(AltExtCXX AltExtCXX.zzz)
+set_property(SOURCE AltExtCXX.zzz PROPERTY LANGUAGE CXX)
diff --git a/Tests/RunCMake/CMP0119/CMP0119-OLD-build-result.txt b/Tests/RunCMake/CMP0119/CMP0119-OLD-build-result.txt
new file mode 100644
index 0000000..d197c91
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMP0119-OLD-build-result.txt
@@ -0,0 +1 @@
+[^0]
diff --git a/Tests/RunCMake/CMP0119/CMP0119-OLD-build-stderr.txt b/Tests/RunCMake/CMP0119/CMP0119-OLD-build-stderr.txt
new file mode 100644
index 0000000..8d98f9d
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMP0119-OLD-build-stderr.txt
@@ -0,0 +1 @@
+.*
diff --git a/Tests/RunCMake/CMP0119/CMP0119-OLD.cmake b/Tests/RunCMake/CMP0119/CMP0119-OLD.cmake
new file mode 100644
index 0000000..9eaa200
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMP0119-OLD.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0119 OLD)
+include(CMP0119-Common.cmake)
diff --git a/Tests/RunCMake/CMP0119/CMP0119-WARN-build-result.txt b/Tests/RunCMake/CMP0119/CMP0119-WARN-build-result.txt
new file mode 100644
index 0000000..d197c91
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMP0119-WARN-build-result.txt
@@ -0,0 +1 @@
+[^0]
diff --git a/Tests/RunCMake/CMP0119/CMP0119-WARN-build-stderr.txt b/Tests/RunCMake/CMP0119/CMP0119-WARN-build-stderr.txt
new file mode 100644
index 0000000..8d98f9d
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMP0119-WARN-build-stderr.txt
@@ -0,0 +1 @@
+.*
diff --git a/Tests/RunCMake/CMP0119/CMP0119-WARN.cmake b/Tests/RunCMake/CMP0119/CMP0119-WARN.cmake
new file mode 100644
index 0000000..00281e9
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMP0119-WARN.cmake
@@ -0,0 +1,2 @@
+
+include(CMP0119-Common.cmake)
diff --git a/Tests/RunCMake/CMP0119/CMakeLists.txt b/Tests/RunCMake/CMP0119/CMakeLists.txt
new file mode 100644
index 0000000..ab1a20c
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/CMakeLists.txt
@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.19)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)
diff --git a/Tests/RunCMake/CMP0119/RunCMakeTest.cmake b/Tests/RunCMake/CMP0119/RunCMakeTest.cmake
new file mode 100644
index 0000000..e547ef5
--- /dev/null
+++ b/Tests/RunCMake/CMP0119/RunCMakeTest.cmake
@@ -0,0 +1,17 @@
+include(RunCMake)
+
+function(run_CMP0119 status)
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/CMP0119-${status}-build)
+  run_cmake(CMP0119-${status})
+  set(RunCMake_TEST_NO_CLEAN 1)
+  run_cmake_command(CMP0119-${status}-build "${CMAKE_COMMAND}" --build . --config Debug)
+endfunction()
+
+if(NOT RunCMake_GENERATOR MATCHES "Visual Studio|Xcode" AND
+    NOT CMAKE_C_COMPILER_ID MATCHES "(Borland|Embarcadero|Watcom)")
+  run_CMP0119(WARN)
+  run_CMP0119(OLD)
+endif()
+if((CMAKE_C_COMPILER_ID MATCHES "(GNU|Clang|MSVC|Borland|Embarcadero|Intel|TI)"))
+  run_CMP0119(NEW)
+endif()