cmStringCommand: Add GENEX_STRIP subcommand.

Strip out any generator expressions in the input string.

Help/command/string.rst

@@ -35,6 +35,7 @@ String operations.
   string(FIND <string> <substring> <output variable> [REVERSE])
   string(TIMESTAMP <output variable> [<format string>] [UTC])
   string(MAKE_C_IDENTIFIER <input string> <output variable>)
+  string(GENEX_STRIP <input string> <output variable>)
 
 REGEX MATCH will match the regular expression once and store the match
 in the output variable.
@@ -154,3 +155,7 @@ If no explicit <format string> is given it will default to:
 
 MAKE_C_IDENTIFIER will write a string which can be used as an
 identifier in C.
+
+``GENEX_STRIP`` will strip any
+:manual:`generator expressions <cmake-generator-expressions(7)>` from the
+``input string`` and store the result in the ``output variable``.

Help/release/dev/string-GENEX_STRIP.rst

@@ -0,0 +1,6 @@
+string-GENEX_STRIP
+------------------
+
+* The :command:`string` command learned a new ``GENEX_STRIP`` subcommand
+  which removes
+  :manual:`generator expression <cmake-generator-expressions(7)>`.

Source/cmStringCommand.cxx

@@ -101,6 +101,10 @@ bool cmStringCommand
     {
     return this->HandleMakeCIdentifierCommand(args);
     }
+  else if(subCommand == "GENEX_STRIP")
+    {
+    return this->HandleGenexStripCommand(args);
+    }
 
   std::string e = "does not recognize sub-command "+subCommand;
   this->SetError(e);
@@ -809,6 +813,27 @@ bool cmStringCommand
   return true;
 }
 
+//----------------------------------------------------------------------------
+bool cmStringCommand
+::HandleGenexStripCommand(std::vector<std::string> const& args)
+{
+  if(args.size() != 3)
+    {
+    this->SetError("sub-command GENEX_STRIP requires two arguments.");
+    return false;
+    }
+
+  const std::string& input = args[1];
+
+  std::string result = cmGeneratorExpression::Preprocess(input,
+                        cmGeneratorExpression::StripAllGeneratorExpressions);
+
+  const std::string& variableName = args[2];
+
+  this->Makefile->AddDefinition(variableName, result.c_str());
+  return true;
+}
+
 //----------------------------------------------------------------------------
 bool cmStringCommand::HandleStripCommand(
   std::vector<std::string> const& args)

Source/cmStringCommand.h

@@ -75,6 +75,7 @@ protected:
   bool HandleFindCommand(std::vector<std::string> const& args);
   bool HandleTimestampCommand(std::vector<std::string> const& args);
   bool HandleMakeCIdentifierCommand(std::vector<std::string> const& args);
+  bool HandleGenexStripCommand(std::vector<std::string> const& args);
 
   class RegexReplacement
   {

Tests/StringFileTest/CMakeLists.txt

@@ -286,3 +286,9 @@ string(MAKE_C_IDENTIFIER "1one-two$" MCI_1)
 if(NOT MCI_1 STREQUAL _1one_two_)
   message(SEND_ERROR "MAKE_C_IDENTIFIER did not create expected result.")
 endif()
+
+string(GENEX_STRIP "one;$<1:two;three>;four;$<TARGET_OBJECTS:some_target>" strip_result)
+
+if (NOT strip_result STREQUAL "one;four")
+  message(SEND_ERROR "GENEX_STRIP did not create expected result: ${strip_result}")
+endif()