ENH: Add install(DIRECTORY) option 'OPTIONAL'

This adds the OPTIONAL option to the install(DIRECTORY) command.  It
tells the installation rule that it is not an error if the source
directory does not exist.  See issue #8394.

Source/cmInstallCommand.cxx

@@ -855,6 +855,7 @@ cmInstallCommand::HandleDirectoryMode(std::vector<std::string> const& args)
                DoingConfigurations, DoingComponent };
   Doing doing = DoingDirs;
   bool in_match_mode = false;
+  bool optional = false;
   std::vector<std::string> dirs;
   const char* destination = 0;
   std::string permissions_file;
@@ -878,6 +879,21 @@ cmInstallCommand::HandleDirectoryMode(std::vector<std::string> const& args)
       // Switch to setting the destination property.
       doing = DoingDestination;
       }
+    else if(args[i] == "OPTIONAL")
+      {
+      if(in_match_mode)
+        {
+        cmOStringStream e;
+        e << args[0] << " does not allow \""
+          << args[i] << "\" after PATTERN or REGEX.";
+        this->SetError(e.str().c_str());
+        return false;
+        }
+
+      // Mark the rule as optional.
+      optional = true;
+      doing = DoingNone;
+      }
     else if(args[i] == "PATTERN")
       {
       // Switch to a new pattern match rule.
@@ -1144,7 +1160,8 @@ cmInstallCommand::HandleDirectoryMode(std::vector<std::string> const& args)
                                     permissions_dir.c_str(),
                                     configurations,
                                     component.c_str(),
-                                    literal_args.c_str()));
+                                    literal_args.c_str(),
+                                    optional));
 
   // Tell the global generator about any installation component names
   // specified.

Source/cmInstallCommand.h

@@ -215,7 +215,7 @@ public:
       "  install(DIRECTORY dirs... DESTINATION <dir>\n"
       "          [FILE_PERMISSIONS permissions...]\n"
       "          [DIRECTORY_PERMISSIONS permissions...]\n"
-      "          [USE_SOURCE_PERMISSIONS]\n"
+      "          [USE_SOURCE_PERMISSIONS] [OPTIONAL]\n"
       "          [CONFIGURATIONS [Debug|Release|...]]\n"
       "          [COMPONENT <component>] [FILES_MATCHING]\n"
       "          [[PATTERN <pattern> | REGEX <regex>]\n"

Source/cmInstallDirectoryGenerator.cxx

@@ -26,10 +26,11 @@ cmInstallDirectoryGenerator
                               const char* dir_permissions,
                               std::vector<std::string> const& configurations,
                               const char* component,
-                              const char* literal_args):
+                              const char* literal_args,
+                              bool optional):
   cmInstallGenerator(dest, configurations, component), Directories(dirs),
   FilePermissions(file_permissions), DirPermissions(dir_permissions),
-  LiteralArguments(literal_args)
+  LiteralArguments(literal_args), Optional(optional)
 {
 }
 
@@ -45,12 +46,11 @@ cmInstallDirectoryGenerator::GenerateScriptActions(std::ostream& os,
                                                    Indent const& indent)
 {
   // Write code to install the directories.
-  bool not_optional = false;
   const char* no_properties = 0;
   const char* no_rename = 0;
   this->AddInstallRule(os, cmTarget::INSTALL_DIRECTORY,
                        this->Directories,
-                       not_optional, no_properties,
+                       this->Optional, no_properties,
                        this->FilePermissions.c_str(),
                        this->DirPermissions.c_str(),
                        no_rename, this->LiteralArguments.c_str(),

Source/cmInstallDirectoryGenerator.h

@@ -31,7 +31,8 @@ public:
                               const char* dir_permissions,
                               std::vector<std::string> const& configurations,
                               const char* component,
-                              const char* literal_args);
+                              const char* literal_args,
+                              bool optional = false);
   virtual ~cmInstallDirectoryGenerator();
 
 protected:
@@ -40,6 +41,7 @@ protected:
   std::string FilePermissions;
   std::string DirPermissions;
   std::string LiteralArguments;
+  bool Optional;
 };
 
 #endif

Tests/SimpleInstall/CMakeLists.txt

@@ -270,6 +270,9 @@ ELSE(STAGE2)
   # Test empty directory installation.
   INSTALL(DIRECTORY DESTINATION MyTest/share/empty)
 
+  # Test optional directory installation.
+  INSTALL(DIRECTORY does-not-exist DESTINATION MyTest/share OPTIONAL)
+
   # Test user-specified install scripts, with and without COMPONENT.
   INSTALL(
     SCRIPT InstallScript1.cmake

Tests/SimpleInstallS2/CMakeLists.txt

@@ -270,6 +270,9 @@ ELSE(STAGE2)
   # Test empty directory installation.
   INSTALL(DIRECTORY DESTINATION MyTest/share/empty)
 
+  # Test optional directory installation.
+  INSTALL(DIRECTORY does-not-exist DESTINATION MyTest/share OPTIONAL)
+
   # Test user-specified install scripts, with and without COMPONENT.
   INSTALL(
     SCRIPT InstallScript1.cmake