Remove the LINK_LANGUAGE generator expression.

It accepted an optional argument to test for equality, but no way
to get the linker language of a particular target.

TARGET_PROPERTY provides this flexibility and STREQUAL provides
the necessary API for equality test.

Extend the CompileDefinitions test to cover accessing the
property of another target.

13 files changed, 53 insertions, 110 deletions

diff --git a/Source/cmAddCompileOptionsCommand.h b/Source/cmAddCompileOptionsCommand.h
index 4504795..e9bbf28 100644
--- a/Source/cmAddCompileOptionsCommand.h
+++ b/Source/cmAddCompileOptionsCommand.h
@@ -62,7 +62,6 @@ public:
       "Arguments to add_compile_options may use \"generator "
       "expressions\" with the syntax \"$<...>\".  "
       CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-      CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS
       ;
     }
 
diff --git a/Source/cmDocumentGeneratorExpressions.h b/Source/cmDocumentGeneratorExpressions.h
index 841061c..46cd77e 100644
--- a/Source/cmDocumentGeneratorExpressions.h
+++ b/Source/cmDocumentGeneratorExpressions.h
@@ -95,12 +95,4 @@
   "the target on which the generator expression is evaluated.\n"        \
   ""
 
-#define CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS                      \
-  "Language related expressions:\n"                                     \
-  "  $<LINK_LANGUAGE>          = The link language of the target "      \
-  "being generated.\n"                                                  \
-  "  $<LINK_LANGUAGE:lang>     = '1' if the link language of the "      \
-  "target being generated matches lang, else '0'.\n"                    \
-  ""
-
 #endif
diff --git a/Source/cmGeneratorExpressionEvaluator.cxx b/Source/cmGeneratorExpressionEvaluator.cxx
index 381ef7c..c1f53b4 100644
--- a/Source/cmGeneratorExpressionEvaluator.cxx
+++ b/Source/cmGeneratorExpressionEvaluator.cxx
@@ -573,69 +573,6 @@ static const struct ConfigurationTestNode : public cmGeneratorExpressionNode
   }
 } configurationTestNode;
 
-//----------------------------------------------------------------------------
-static const struct LinkLanguageNode : public cmGeneratorExpressionNode
-{
-  LinkLanguageNode() {}
-
-  virtual int NumExpectedParameters() const { return ZeroOrMoreParameters; }
-
-  std::string Evaluate(const std::vector<std::string> &parameters,
-                       cmGeneratorExpressionContext *context,
-                       const GeneratorExpressionContent *content,
-                       cmGeneratorExpressionDAGChecker *dagChecker) const
-  {
-    if (dagChecker && dagChecker->EvaluatingLinkLibraries())
-      {
-      reportError(context, content->GetOriginalExpression(),
-          "$<LINK_LANGUAGE> expression can not be used while evaluating "
-          "link libraries");
-      return std::string();
-      }
-    if (parameters.size() != 0 && parameters.size() != 1)
-      {
-      reportError(context, content->GetOriginalExpression(),
-          "$<LINK_LANGUAGE> expression requires one or two parameters");
-      return std::string();
-      }
-    cmTarget* target = context->HeadTarget;
-    if (!target)
-      {
-      reportError(context, content->GetOriginalExpression(),
-          "$<LINK_LANGUAGE> may only be used with targets.  It may not "
-          "be used with add_custom_command.");
-      return std::string();
-      }
-
-    const char *lang = target->GetLinkerLanguage(context->Config);
-    if (parameters.size() == 0)
-      {
-      return lang ? lang : "";
-      }
-    else
-      {
-      cmsys::RegularExpression langValidator;
-      langValidator.compile("^[A-Za-z0-9_]*$");
-      if (!langValidator.find(parameters.begin()->c_str()))
-        {
-        reportError(context, content->GetOriginalExpression(),
-                    "Expression syntax not recognized.");
-        return std::string();
-        }
-      if (!lang)
-        {
-        return parameters.front().empty() ? "1" : "0";
-        }
-
-      if (strcmp(parameters.begin()->c_str(), lang) == 0)
-        {
-        return "1";
-        }
-      return "0";
-      }
-  }
-} linkLanguageNode;
-
 static const struct JoinNode : public cmGeneratorExpressionNode
 {
   JoinNode() {}
@@ -835,6 +772,19 @@ static const struct TargetPropertyNode : public cmGeneratorExpressionNode
 
     assert(target);
 
+    if (propertyName == "LINKER_LANGUAGE")
+      {
+      if (dagCheckerParent && dagCheckerParent->EvaluatingLinkLibraries())
+        {
+        reportError(context, content->GetOriginalExpression(),
+            "LINKER_LANGUAGE target property can not be used while evaluating "
+            "link libraries");
+        return std::string();
+        }
+      const char *lang = target->GetLinkerLanguage(context->Config);
+      return lang ? lang : "";
+      }
+
     cmGeneratorExpressionDAGChecker dagChecker(context->Backtrace,
                                                target->GetName(),
                                                propertyName,
@@ -1380,8 +1330,6 @@ cmGeneratorExpressionNode* GetNode(const std::string &identifier)
     return &configurationNode;
   else if (identifier == "CONFIG")
     return &configurationTestNode;
-  else if (identifier == "LINK_LANGUAGE")
-    return &linkLanguageNode;
   else if (identifier == "TARGET_FILE")
     return &targetFileNode;
   else if (identifier == "TARGET_LINKER_FILE")
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index 818a580..2cd19cf 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -4087,8 +4087,7 @@ void cmMakefile::DefineProperties(cmake *cm)
      "the options for the compiler.\n"
      "Contents of COMPILE_OPTIONS may use \"generator expressions\" with "
      "the syntax \"$<...>\".  "
-     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
+     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("LINK_DIRECTORIES", cmProperty::DIRECTORY,
diff --git a/Source/cmTarget.cxx b/Source/cmTarget.cxx
index 70500cd..f8cecd1 100644
--- a/Source/cmTarget.cxx
+++ b/Source/cmTarget.cxx
@@ -292,7 +292,6 @@ void cmTarget::DefineProperties(cmake *cm)
      "Contents of COMPILE_DEFINITIONS may use \"generator expressions\" with "
      "the syntax \"$<...>\".  "
      CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS
      CM_DOCUMENT_COMPILE_DEFINITIONS_DISCLAIMER);
 
   cm->DefineProperty
@@ -311,8 +310,7 @@ void cmTarget::DefineProperties(cmake *cm)
      "the options for the compiler.\n"
      "Contents of COMPILE_OPTIONS may use \"generator expressions\" with "
      "the syntax \"$<...>\".  "
-     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
+     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("INTERFACE_COMPILE_OPTIONS", cmProperty::TARGET,
@@ -323,8 +321,7 @@ void cmTarget::DefineProperties(cmake *cm)
      "as $<TARGET_PROPERTY:foo,INTERFACE_COMPILE_OPTIONS> to use the "
      "compile options specified in the interface of 'foo'."
      "\n"
-     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
+     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("DEFINE_SYMBOL", cmProperty::TARGET,
@@ -653,8 +650,7 @@ void cmTarget::DefineProperties(cmake *cm)
      "See also the include_directories command.\n"
      "Contents of INCLUDE_DIRECTORIES may use \"generator expressions\" with "
      "the syntax \"$<...>\".  "
-     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
+     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("INSTALL_NAME_DIR", cmProperty::TARGET,
@@ -749,7 +745,11 @@ void cmTarget::DefineProperties(cmake *cm)
      "file providing the program entry point (main).  "
      "If not set, the language with the highest linker preference "
      "value is the default.  "
-     "See documentation of CMAKE_<LANG>_LINKER_PREFERENCE variables.");
+     "See documentation of CMAKE_<LANG>_LINKER_PREFERENCE variables."
+     "\n"
+     "If this property is not set by the user, it will be calculated at "
+     "generate-time by CMake."
+    );
 
   cm->DefineProperty
     ("LOCATION", cmProperty::TARGET,
@@ -870,8 +870,7 @@ void cmTarget::DefineProperties(cmake *cm)
      "as $<TARGET_PROPERTY:foo,INTERFACE_INCLUDE_DIRECTORIES> to use the "
      "include directories specified in the interface of 'foo'."
      "\n"
-     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
+     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("SYSTEM_INTERFACE_INCLUDE_DIRECTORIES", cmProperty::TARGET,
@@ -881,8 +880,7 @@ void cmTarget::DefineProperties(cmake *cm)
      "compiler warnings.  Consuming targets will then mark the same include "
      "directories as system headers."
      "\n"
-     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
+     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("INTERFACE_COMPILE_DEFINITIONS", cmProperty::TARGET,
@@ -893,8 +891,7 @@ void cmTarget::DefineProperties(cmake *cm)
      "as $<TARGET_PROPERTY:foo,INTERFACE_COMPILE_DEFINITIONS> to use the "
      "compile definitions specified in the interface of 'foo'."
      "\n"
-     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
+     CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("LINK_INTERFACE_MULTIPLICITY", cmProperty::TARGET,
diff --git a/Source/cmTargetCompileDefinitionsCommand.h b/Source/cmTargetCompileDefinitionsCommand.h
index bc58b31..585485d 100644
--- a/Source/cmTargetCompileDefinitionsCommand.h
+++ b/Source/cmTargetCompileDefinitionsCommand.h
@@ -70,7 +70,6 @@ public:
       "Arguments to target_compile_definitions may use \"generator "
       "expressions\" with the syntax \"$<...>\".  "
       CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-      CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS
       ;
     }
 
diff --git a/Source/cmTargetIncludeDirectoriesCommand.h b/Source/cmTargetIncludeDirectoriesCommand.h
index 2968618..fcc37f0 100644
--- a/Source/cmTargetIncludeDirectoriesCommand.h
+++ b/Source/cmTargetIncludeDirectoriesCommand.h
@@ -83,7 +83,6 @@ public:
       "Arguments to target_include_directories may use \"generator "
       "expressions\" with the syntax \"$<...>\".  "
       CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
-      CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS
       ;
     }
 
diff --git a/Tests/CompileDefinitions/compiletest_mixed_c.c b/Tests/CompileDefinitions/compiletest_mixed_c.c
index 698c989..a270b2b 100644
--- a/Tests/CompileDefinitions/compiletest_mixed_c.c
+++ b/Tests/CompileDefinitions/compiletest_mixed_c.c
@@ -13,6 +13,10 @@
 #error Unexpected LINK_LANGUAGE_IS_C
 #endif
 
+#ifndef C_EXECUTABLE_LINK_LANGUAGE_IS_C
+#error Expected C_EXECUTABLE_LINK_LANGUAGE_IS_C define
+#endif
+
 void someFunc(void)
 {
 
diff --git a/Tests/CompileDefinitions/compiletest_mixed_cxx.cpp b/Tests/CompileDefinitions/compiletest_mixed_cxx.cpp
index c686854..ae6befc 100644
--- a/Tests/CompileDefinitions/compiletest_mixed_cxx.cpp
+++ b/Tests/CompileDefinitions/compiletest_mixed_cxx.cpp
@@ -13,6 +13,10 @@
 #error Unexpected LINK_LANGUAGE_IS_C
 #endif
 
+#ifndef C_EXECUTABLE_LINK_LANGUAGE_IS_C
+#error Expected C_EXECUTABLE_LINK_LANGUAGE_IS_C define
+#endif
+
 int main(int argc, char **argv)
 {
   return 0;
diff --git a/Tests/CompileDefinitions/target_prop/CMakeLists.txt b/Tests/CompileDefinitions/target_prop/CMakeLists.txt
index 6bf9c5c..a0d3f4e 100644
--- a/Tests/CompileDefinitions/target_prop/CMakeLists.txt
+++ b/Tests/CompileDefinitions/target_prop/CMakeLists.txt
@@ -23,9 +23,9 @@ set_property(TARGET target_prop_executable APPEND PROPERTY COMPILE_DEFINITIONS
     LETTER_LIST3=\"$<JOIN:A;B;C;D,,->\"
     LETTER_LIST4=\"$<JOIN:A;B;C;D,-,->\"
     LETTER_LIST5=\"$<JOIN:A;B;C;D,-,>\"
-    "$<$<LINK_LANGUAGE:CXX>:LINK_CXX_DEFINE>"
-    "$<$<LINK_LANGUAGE:C>:LINK_C_DEFINE>"
-    "LINK_LANGUAGE_IS_$<LINK_LANGUAGE>"
+    "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,CXX>:LINK_CXX_DEFINE>"
+    "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,C>:LINK_C_DEFINE>"
+    "LINK_LANGUAGE_IS_$<TARGET_PROPERTY:LINKER_LANGUAGE>"
 )
 
 set_property(TARGET target_prop_executable APPEND PROPERTY COMPILE_DEFINITIONS
@@ -36,16 +36,17 @@ set_property(TARGET target_prop_executable APPEND PROPERTY COMPILE_DEFINITIONS
 add_executable(target_prop_c_executable ../compiletest.c)
 
 set_property(TARGET target_prop_c_executable APPEND PROPERTY COMPILE_DEFINITIONS
-    "$<$<LINK_LANGUAGE:CXX>:LINK_CXX_DEFINE>"
-    "$<$<LINK_LANGUAGE:C>:LINK_C_DEFINE>"
-    "LINK_LANGUAGE_IS_$<LINK_LANGUAGE>"
+    "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,CXX>:LINK_CXX_DEFINE>"
+    "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,C>:LINK_C_DEFINE>"
+    "LINK_LANGUAGE_IS_$<TARGET_PROPERTY:LINKER_LANGUAGE>"
     )
 
 # Resulting link language will be CXX
 add_executable(target_prop_mixed_executable ../compiletest_mixed_c.c ../compiletest_mixed_cxx.cpp)
 
 set_property(TARGET target_prop_mixed_executable APPEND PROPERTY COMPILE_DEFINITIONS
-    "$<$<LINK_LANGUAGE:CXX>:LINK_CXX_DEFINE>"
-    "$<$<LINK_LANGUAGE:C>:LINK_C_DEFINE>"
-    "LINK_LANGUAGE_IS_$<LINK_LANGUAGE>"
+    "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,CXX>:LINK_CXX_DEFINE>"
+    "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,C>:LINK_C_DEFINE>"
+    "LINK_LANGUAGE_IS_$<TARGET_PROPERTY:LINKER_LANGUAGE>"
+    "C_EXECUTABLE_LINK_LANGUAGE_IS_$<TARGET_PROPERTY:target_prop_c_executable,LINKER_LANGUAGE>"
     )
diff --git a/Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt b/Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt
index 6919261..8e2bd0a 100644
--- a/Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt
+++ b/Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt
@@ -156,15 +156,15 @@ target_include_directories(TargetIncludeDirectories PRIVATE "${CMAKE_CURRENT_BIN
 # Test that the language generator expressions work
 set_property(TARGET TargetIncludeDirectories
   APPEND PROPERTY INCLUDE_DIRECTORIES
-  "$<$<LINK_LANGUAGE:C>:${CMAKE_CURRENT_BINARY_DIR}/bad>"
-  "$<$<LINK_LANGUAGE:CXX>:${CMAKE_CURRENT_BINARY_DIR}/good>"
-  "$<$<STREQUAL:$<LINK_LANGUAGE>,CXX>:${CMAKE_CURRENT_BINARY_DIR}/othergood/>"
+  "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,C>:${CMAKE_CURRENT_BINARY_DIR}/bad>"
+  "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,CXX>:${CMAKE_CURRENT_BINARY_DIR}/good>"
+  "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,CXX>:${CMAKE_CURRENT_BINARY_DIR}/othergood/>"
 )
 
 add_executable(TargetIncludeDirectories_C main.c)
 set_property(TARGET TargetIncludeDirectories_C
   APPEND PROPERTY INCLUDE_DIRECTORIES
-  "$<$<LINK_LANGUAGE:CXX>:${CMAKE_CURRENT_BINARY_DIR}/bad>"
-  "$<$<LINK_LANGUAGE:C>:${CMAKE_CURRENT_BINARY_DIR}/good>"
-  "$<$<STREQUAL:$<LINK_LANGUAGE>,C>:${CMAKE_CURRENT_BINARY_DIR}/othergood/>"
+  "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,CXX>:${CMAKE_CURRENT_BINARY_DIR}/bad>"
+  "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,C>:${CMAKE_CURRENT_BINARY_DIR}/good>"
+  "$<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,C>:${CMAKE_CURRENT_BINARY_DIR}/othergood/>"
 )
diff --git a/Tests/RunCMake/Languages/LINK_LANGUAGE-genex-stderr.txt b/Tests/RunCMake/Languages/LINK_LANGUAGE-genex-stderr.txt
index 8e0591d..a5d5d50 100644
--- a/Tests/RunCMake/Languages/LINK_LANGUAGE-genex-stderr.txt
+++ b/Tests/RunCMake/Languages/LINK_LANGUAGE-genex-stderr.txt
@@ -1,6 +1,7 @@
 CMake Error:
   Error evaluating generator expression:
 
-    \$<LINK_LANGUAGE>
+    \$<TARGET_PROPERTY:LINKER_LANGUAGE>
 
-  \$<LINK_LANGUAGE> expression can not be used while evaluating link libraries
+  LINKER_LANGUAGE target property can not be used while evaluating link
+  libraries
diff --git a/Tests/RunCMake/Languages/LINK_LANGUAGE-genex.cmake b/Tests/RunCMake/Languages/LINK_LANGUAGE-genex.cmake
index e0f8c57..d4e31cd 100644
--- a/Tests/RunCMake/Languages/LINK_LANGUAGE-genex.cmake
+++ b/Tests/RunCMake/Languages/LINK_LANGUAGE-genex.cmake
@@ -1,4 +1,4 @@
 
 add_library(foo SHARED empty.cpp)
 add_library(bar SHARED empty.cpp)
-target_link_libraries(foo $<$<STREQUAL:$<LINK_LANGUAGE>,anything>:bar>)
+target_link_libraries(foo $<$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,anything>:bar>)