cmSourceFile: Move LANGUAGE to GetPropertyForUser

- Remove the special case from cmGetSourceFilePropertyCommand

Tests: check LANGUAGE for source file
- use target_sources to add file
- use get_property to read property value

3 files changed, 17 insertions, 11 deletions

diff --git a/Source/cmGetSourceFilePropertyCommand.cxx b/Source/cmGetSourceFilePropertyCommand.cxx
index 5a477b9..5c1c8a5 100644
--- a/Source/cmGetSourceFilePropertyCommand.cxx
+++ b/Source/cmGetSourceFilePropertyCommand.cxx
@@ -24,10 +24,6 @@ bool cmGetSourceFilePropertyCommand::InitialPass(
     sf = this->Makefile->CreateSource(file);
   }
   if (sf) {
-    if (args[2] == "LANGUAGE") {
-      this->Makefile->AddDefinition(var, sf->GetOrDetermineLanguage());
-      return true;
-    }
     const char* prop = nullptr;
     if (!args[2].empty()) {
       prop = sf->GetPropertyForUser(args[2]);
diff --git a/Source/cmSourceFile.cxx b/Source/cmSourceFile.cxx
index 738a1c0..5d738d5 100644
--- a/Source/cmSourceFile.cxx
+++ b/Source/cmSourceFile.cxx
@@ -272,6 +272,13 @@ const char* cmSourceFile::GetPropertyForUser(const std::string& prop)
     this->GetFullPath();
   }
 
+  // Similarly, LANGUAGE can be determined by the file extension
+  // if it is requested by the user.
+  if (prop == propLANGUAGE) {
+    // The c_str pointer is valid until `this->Language` is modified.
+    return this->GetOrDetermineLanguage().c_str();
+  }
+
   // Perform the normal property lookup.
   return this->GetProperty(prop);
 }
diff --git a/Tests/SourceFileProperty/CMakeLists.txt b/Tests/SourceFileProperty/CMakeLists.txt
index 1b6506d..5dbc34f 100644
--- a/Tests/SourceFileProperty/CMakeLists.txt
+++ b/Tests/SourceFileProperty/CMakeLists.txt
@@ -1,19 +1,22 @@
-cmake_minimum_required(VERSION 3.0)
+cmake_minimum_required(VERSION 3.1)
 project(SourceFileProperty C)
 
-set(sources)
-
 if (EXISTS icasetest.c)
   # If a file exists by this name, use it.
   set_source_files_properties(icasetest.c
     PROPERTIES
-      COMPILE_FLAGS -DNEEDED_TO_WORK)
+      COMPILE_DEFINITIONS NEEDED_TO_WORK)
 else ()
   # Work on case-sensitive file systems as well.
   set_source_files_properties(main.c
     PROPERTIES
-      COMPILE_FLAGS -DNO_NEED_TO_CALL)
+      COMPILE_DEFINITIONS NO_NEED_TO_CALL)
 endif ()
-list(APPEND sources ICaseTest.c)
 
-add_executable(SourceFileProperty main.c ${sources})
+add_executable(SourceFileProperty main.c)
+target_sources(SourceFileProperty PRIVATE ICaseTest.c)
+
+get_property(LANG SOURCE ICaseTest.c PROPERTY LANGUAGE)
+if (NOT "${LANG}" STREQUAL "C")
+  message(FATAL_ERROR "Bad language for file ICaseTest.c")
+endif ()