file: Add GENERATE command to produce files at generate time

The idea is to write to a temp file which contains generator
expressions, and at generate time, evaluate the generator expressions,
and write the result to a file.

Because executables on Windows are limited in the length of command line
it is possible to use, it is common to write command line arguments to a
file instead and specify the file as a source of arguments.

This new FILE(GENERATE) subcommand allows the use of generator
expressions to create such files so that they can be used with
add_custom_command for example.

1 files changed, 19 insertions, 0 deletions

diff --git a/Source/cmFileCommand.h b/Source/cmFileCommand.h
index 5973fa7..586fee2 100644
--- a/Source/cmFileCommand.h
+++ b/Source/cmFileCommand.h
@@ -88,6 +88,9 @@ public:
       "  file(UPLOAD filename url [INACTIVITY_TIMEOUT timeout]\n"
       "       [TIMEOUT timeout] [STATUS status] [LOG log] [SHOW_PROGRESS])\n"
       "  file(TIMESTAMP filename variable [<format string>] [UTC])\n"
+      "  file(GENERATE OUTPUT output_file\n"
+      "       <INPUT input_file|CONTENT input_content>\n"
+      "       CONDITION expression)\n"
       "WRITE will write a message into a file called 'filename'. It "
       "overwrites the file if it already exists, and creates the file "
       "if it does not exist. (If the file is a build input, use "
@@ -231,6 +234,15 @@ public:
       "it prints status messages, and NO_SOURCE_PERMISSIONS is default.  "
       "Installation scripts generated by the install() command use this "
       "signature (with some undocumented options for internal use)."
+      "\n"
+      "GENERATE will write an <output_file> with content from an "
+      "<input_file>, or from <input_content>.  The output is generated "
+      "conditionally based on the content of the <condition>.  The file is "
+      "written at CMake generate-time and the input may contain generator "
+      "expressions.  The <condition>, <output_file> and <input_file> may "
+      "also contain generator expressions.  The <condition> must evaluate to "
+      "either '0' or '1'.  The <output_file> must evaluate to a unique name "
+      "among all configurations and among all invocations of file(GENERATE)."
       // Undocumented INSTALL options:
       //  - RENAME <name>
       //  - OPTIONAL
@@ -269,6 +281,13 @@ protected:
   bool HandleUploadCommand(std::vector<std::string> const& args);
 
   bool HandleTimestampCommand(std::vector<std::string> const& args);
+  bool HandleGenerateCommand(std::vector<std::string> const& args);
+
+private:
+  void AddEvaluationFile(const std::string &inputName,
+                         const std::string &outputExpr,
+                         const std::string &condition,
+                         bool inputIsContent);
 };