Add $<LINK_LANGUAGE> generator expression

They can't be used when evaluating link libraries, but they can be
used for include directories and compile definitions. Later they can
be used for compile options.

Source/cmDocumentGeneratorExpressions.h

@@ -74,4 +74,12 @@
   "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

Source/cmGeneratorExpressionEvaluator.cxx

@@ -45,6 +45,11 @@ void reportError(cmGeneratorExpressionContext *context,
 //----------------------------------------------------------------------------
 struct cmGeneratorExpressionNode
 {
+  enum {
+    DynamicParameters = 0,
+    OneOrMoreParameters = -1,
+    ZeroOrMoreParameters = -2
+  };
   virtual ~cmGeneratorExpressionNode() {}
 
   virtual bool GeneratesContent() const { return true; }
@@ -110,8 +115,7 @@ static const struct ZeroNode installInterfaceNode;
 static const struct OP ## Node : public cmGeneratorExpressionNode \
 { \
   OP ## Node () {} \
-/* We let -1 carry the meaning 'at least one' */ \
-  virtual int NumExpectedParameters() const { return -1; } \
+  virtual int NumExpectedParameters() const { return OneOrMoreParameters; } \
  \
   std::string Evaluate(const std::vector<std::string> &parameters, \
                        cmGeneratorExpressionContext *context, \
@@ -306,6 +310,60 @@ 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 *) const
+  {
+    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.");
+      }
+
+    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
 {
@@ -347,7 +405,7 @@ static const struct TargetPropertyNode : public cmGeneratorExpressionNode
   TargetPropertyNode() {}
 
   // This node handles errors on parameter count itself.
-  virtual int NumExpectedParameters() const { return -1; }
+  virtual int NumExpectedParameters() const { return OneOrMoreParameters; }
 
   std::string Evaluate(const std::vector<std::string> &parameters,
                        cmGeneratorExpressionContext *context,
@@ -961,6 +1019,8 @@ 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")
@@ -1188,7 +1248,8 @@ std::string GeneratorExpressionContent::EvaluateParameters(
     }
   }
 
-  if ((numExpected != -1 && (unsigned int)numExpected != parameters.size()))
+  if ((numExpected > cmGeneratorExpressionNode::DynamicParameters
+      && (unsigned int)numExpected != parameters.size()))
     {
     if (numExpected == 0)
       {
@@ -1213,7 +1274,8 @@ std::string GeneratorExpressionContent::EvaluateParameters(
     return std::string();
     }
 
-  if (numExpected == -1 && parameters.empty())
+  if (numExpected == cmGeneratorExpressionNode::OneOrMoreParameters
+      && parameters.empty())
     {
     reportError(context, this->GetOriginalExpression(), "$<" + identifier
                       + "> expression requires at least one parameter.");

Source/cmTarget.cxx

@@ -277,6 +277,7 @@ 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
@@ -605,7 +606,8 @@ 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_COMMAND_GENERATOR_EXPRESSIONS
+     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("INSTALL_NAME_DIR", cmProperty::TARGET,
@@ -802,7 +804,8 @@ 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_COMMAND_GENERATOR_EXPRESSIONS
+     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("INTERFACE_COMPILE_DEFINITIONS", cmProperty::TARGET,
@@ -813,7 +816,8 @@ 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_COMMAND_GENERATOR_EXPRESSIONS
+     CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS);
 
   cm->DefineProperty
     ("LINK_INTERFACE_MULTIPLICITY", cmProperty::TARGET,

Source/cmTargetCompileDefinitionsCommand.h

@@ -70,6 +70,7 @@ public:
       "Arguments to target_compile_definitions may use \"generator "
       "expressions\" with the syntax \"$<...>\".  "
       CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
+      CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS
       ;
     }
 

Source/cmTargetIncludeDirectoriesCommand.h

@@ -75,6 +75,7 @@ public:
       "Arguments to target_include_directories may use \"generator "
       "expressions\" with the syntax \"$<...>\".  "
       CM_DOCUMENT_COMMAND_GENERATOR_EXPRESSIONS
+      CM_DOCUMENT_LANGUAGE_GENERATOR_EXPRESSIONS
       ;
     }
 

Tests/CompileDefinitions/compiletest.c

+
+#ifndef LINK_C_DEFINE
+#error Expected LINK_C_DEFINE
+#endif
+#ifndef LINK_LANGUAGE_IS_C
+#error Expected LINK_LANGUAGE_IS_C
+#endif
+
+#ifdef LINK_CXX_DEFINE
+#error Unexpected LINK_CXX_DEFINE
+#endif
+#ifdef LINK_LANGUAGE_IS_CXX
+#error Unexpected LINK_LANGUAGE_IS_CXX
+#endif
+
+int main(void)
+{
+  return 0;
+}

Tests/CompileDefinitions/compiletest.cpp

@@ -56,6 +56,21 @@ enum {
 #error Expect PREFIX_DEF2
 #endif
 
+#ifndef LINK_CXX_DEFINE
+#error Expected LINK_CXX_DEFINE
+#endif
+#ifndef LINK_LANGUAGE_IS_CXX
+#error Expected LINK_LANGUAGE_IS_CXX
+#endif
+
+#ifdef LINK_C_DEFINE
+#error Unexpected LINK_C_DEFINE
+#endif
+#ifdef LINK_LANGUAGE_IS_C
+#error Unexpected LINK_LANGUAGE_IS_C
+#endif
+
+
 // TEST_GENERATOR_EXPRESSIONS
 #endif
 

Tests/CompileDefinitions/compiletest_mixed_c.c

+
+#ifndef LINK_CXX_DEFINE
+#error Expected LINK_CXX_DEFINE
+#endif
+#ifndef LINK_LANGUAGE_IS_CXX
+#error Expected LINK_LANGUAGE_IS_CXX
+#endif
+
+#ifdef LINK_C_DEFINE
+#error Unexpected LINK_C_DEFINE
+#endif
+#ifdef LINK_LANGUAGE_IS_C
+#error Unexpected LINK_LANGUAGE_IS_C
+#endif
+
+void someFunc(void)
+{
+
+}

Tests/CompileDefinitions/compiletest_mixed_cxx.cpp

+
+#ifndef LINK_CXX_DEFINE
+#error Expected LINK_CXX_DEFINE
+#endif
+#ifndef LINK_LANGUAGE_IS_CXX
+#error Expected LINK_LANGUAGE_IS_CXX
+#endif
+
+#ifdef LINK_C_DEFINE
+#error Unexpected LINK_C_DEFINE
+#endif
+#ifdef LINK_LANGUAGE_IS_C
+#error Unexpected LINK_LANGUAGE_IS_C
+#endif
+
+int main(int argc, char **argv)
+{
+  return 0;
+}

Tests/CompileDefinitions/target_prop/CMakeLists.txt

@@ -19,9 +19,29 @@ 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>"
 )
 
 set_property(TARGET target_prop_executable APPEND PROPERTY COMPILE_DEFINITIONS
   BUILD_IS_DEBUG=$<CONFIG:Debug>
   BUILD_IS_NOT_DEBUG=$<NOT:$<CONFIG:Debug>>
   )
+
+add_executable(target_prop_c_executable ../compiletest.c)
+
+set_property(TARGET target_prop_c_executable APPEND PROPERTY COMPILE_DEFINITIONS
+    "$<$<LINK_LANGUAGE:CXX>:LINK_CXX_DEFINE>"
+    "$<$<LINK_LANGUAGE:C>:LINK_C_DEFINE>"
+    "LINK_LANGUAGE_IS_$<LINK_LANGUAGE>"
+    )
+
+# 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>"
+    )

Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt

@@ -128,3 +128,19 @@ file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/prefix_foo/prefix_bar/prefix_ba
 file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/prefix_foo/prefix_bar/prefix_bat/prefix_foo_bar_bat.h" "// prefix_foo_bar_bat.h\n")
 
 target_include_directories(TargetIncludeDirectories PRIVATE "${CMAKE_CURRENT_BINARY_DIR}/prefix_$<JOIN:foo;bar;bat,/prefix_>")
+
+# 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/>"
+)
+
+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/>"
+)

Tests/IncludeDirectories/TargetIncludeDirectories/main.c

+
+#include "common.h"
+
+int main(void)
+{
+  return 0;
+}

Tests/IncludeDirectories/TargetIncludeDirectories/main.cpp

@@ -11,6 +11,7 @@
 #include "list.h"
 #include "target.h"
 #include "prefix_foo_bar_bat.h"
+#include "common.h"
 
 int main(int, char**)
 {