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.

13 files changed, 200 insertions, 8 deletions

diff --git a/Source/cmDocumentGeneratorExpressions.h b/Source/cmDocumentGeneratorExpressions.h
index ac52db0..93e9cec 100644
--- a/Source/cmDocumentGeneratorExpressions.h
+++ b/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
diff --git a/Source/cmGeneratorExpressionEvaluator.cxx b/Source/cmGeneratorExpressionEvaluator.cxx
index 6092aa2..7870d37 100644
--- a/Source/cmGeneratorExpressionEvaluator.cxx
+++ b/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(), "$<" + identifier
                       + "> expression requires at least one parameter.");
diff --git a/Source/cmTarget.cxx b/Source/cmTarget.cxx
index d14bfca..865a4da 100644
--- a/Source/cmTarget.cxx
+++ b/Source/cmTarget.cxx
@@ -277,6 +277,7 @@ void cmTarget::DefineProperties(cmake *cm)
      "Contents of COMPILE_DEFINITIONS may use \"generator expressions\" with "
      "the syntax \"$<...>\".  "
      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,
diff --git a/Source/cmTargetCompileDefinitionsCommand.h b/Source/cmTargetCompileDefinitionsCommand.h
index ec9b071..22d8fa8 100644
--- a/Source/cmTargetCompileDefinitionsCommand.h
+++ b/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
       ;
     }
 
diff --git a/Source/cmTargetIncludeDirectoriesCommand.h b/Source/cmTargetIncludeDirectoriesCommand.h
index e4bc9cf..4a1a4df 100644
--- a/Source/cmTargetIncludeDirectoriesCommand.h
+++ b/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
       ;
     }
 
diff --git a/Tests/CompileDefinitions/compiletest.c b/Tests/CompileDefinitions/compiletest.c
new file mode 100644
index 0000000..d7883af
--- /dev/null
+++ b/Tests/CompileDefinitions/compiletest.c
@@ -0,0 +1,19 @@
+
+#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;
+}
diff --git a/Tests/CompileDefinitions/compiletest.cpp b/Tests/CompileDefinitions/compiletest.cpp
index 7379380..7df09df 100644
--- a/Tests/CompileDefinitions/compiletest.cpp
+++ b/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
 
diff --git a/Tests/CompileDefinitions/compiletest_mixed_c.c b/Tests/CompileDefinitions/compiletest_mixed_c.c
new file mode 100644
index 0000000..698c989
--- /dev/null
+++ b/Tests/CompileDefinitions/compiletest_mixed_c.c
@@ -0,0 +1,19 @@
+
+#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)
+{
+
+}
diff --git a/Tests/CompileDefinitions/compiletest_mixed_cxx.cpp b/Tests/CompileDefinitions/compiletest_mixed_cxx.cpp
new file mode 100644
index 0000000..c686854
--- /dev/null
+++ b/Tests/CompileDefinitions/compiletest_mixed_cxx.cpp
@@ -0,0 +1,19 @@
+
+#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;
+}
diff --git a/Tests/CompileDefinitions/target_prop/CMakeLists.txt b/Tests/CompileDefinitions/target_prop/CMakeLists.txt
index 34be917..66a3aa6 100644
--- a/Tests/CompileDefinitions/target_prop/CMakeLists.txt
+++ b/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_$<LINK_LANGUAGE>"
+    )
diff --git a/Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt b/Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt
index 60d4c6a..50f12ee 100644
--- a/Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt
+++ b/Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt
@@ -128,3 +128,19 @@ file(MAKE_DIRECTORY "${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/>"
+)
diff --git a/Tests/IncludeDirectories/TargetIncludeDirectories/main.c b/Tests/IncludeDirectories/TargetIncludeDirectories/main.c
new file mode 100644
index 0000000..a597daa
--- /dev/null
+++ b/Tests/IncludeDirectories/TargetIncludeDirectories/main.c
@@ -0,0 +1,7 @@
+
+#include "common.h"
+
+int main(void)
+{
+  return 0;
+}
diff --git a/Tests/IncludeDirectories/TargetIncludeDirectories/main.cpp b/Tests/IncludeDirectories/TargetIncludeDirectories/main.cpp
index 5bb34aa..aed0bde 100644
--- a/Tests/IncludeDirectories/TargetIncludeDirectories/main.cpp
+++ b/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**)
 {