file(INSTALL): Improve formatting of symlink creation error

Avoid printing two error messages.  Format paths without wrapping.

Source/cmFileCopier.cxx

@@ -504,11 +504,12 @@ bool cmFileCopier::InstallSymlinkChain(std::string& fromFile,
       cmSystemTools::RemoveFile(toFile);
       cmSystemTools::MakeDirectory(toFilePath);
 
-      if (!cmSystemTools::CreateSymlink(symlinkTarget, toFile)) {
-        std::ostringstream e;
-        e << this->Name << " cannot create symlink \"" << toFile
-          << "\": " << cmSystemTools::GetLastSystemError() << ".";
-        this->Status.SetError(e.str());
+      cmsys::Status status =
+        cmSystemTools::CreateSymlinkQuietly(symlinkTarget, toFile);
+      if (!status) {
+        std::string e = cmStrCat(this->Name, " cannot create symlink\n  ",
+                                 toFile, "\nbecause: ", status.GetString());
+        this->Status.SetError(e);
         return false;
       }
     }
@@ -557,12 +558,13 @@ bool cmFileCopier::InstallSymlink(const std::string& fromFile,
     cmSystemTools::MakeDirectory(cmSystemTools::GetFilenamePath(toFile));
 
     // Create the symlink.
-    if (!cmSystemTools::CreateSymlink(symlinkTarget, toFile)) {
-      std::ostringstream e;
-      e << this->Name << " cannot duplicate symlink \"" << fromFile
-        << "\" at \"" << toFile
-        << "\": " << cmSystemTools::GetLastSystemError() << ".";
-      this->Status.SetError(e.str());
+    cmsys::Status status =
+      cmSystemTools::CreateSymlinkQuietly(symlinkTarget, toFile);
+    if (!status) {
+      std::string e =
+        cmStrCat(this->Name, " cannot duplicate symlink\n  ", fromFile,
+                 "\nat\n  ", toFile, "\nbecause: ", status.GetString());
+      this->Status.SetError(e);
       return false;
     }
   }

Tests/RunCMake/install/DIRECTORY-symlink-clobber-all-result.txt

@@ -0,0 +1 @@
+1

Tests/RunCMake/install/DIRECTORY-symlink-clobber-all-stderr.txt

@@ -0,0 +1,12 @@
+^CMake Error at cmake_install.cmake:[0-9]+ \(file\):
+  file INSTALL cannot duplicate symlink
+
+    [^
+]*/Tests/RunCMake/install/DIRECTORY-symlink-clobber-build/new/dir
+
+  at
+
+    [^
+]*/Tests/RunCMake/install/DIRECTORY-symlink-clobber-build/root-all/dest/dir
+
+  because:

Tests/RunCMake/install/DIRECTORY-symlink-clobber-all-stdout.txt

@@ -0,0 +1,12 @@
+-- Installing: [^
+]*/Tests/RunCMake/install/DIRECTORY-symlink-clobber-build/root-all/dest/dir
+-- Installing: [^
+]*/Tests/RunCMake/install/DIRECTORY-symlink-clobber-build/root-all/dest/dir/file
+-- Installing: [^
+]*/Tests/RunCMake/install/DIRECTORY-symlink-clobber-build/root-all/dest/lnk
+-- Up-to-date: [^
+]*/Tests/RunCMake/install/DIRECTORY-symlink-clobber-build/root-all/dest/lnk
+-- Up-to-date: [^
+]*/Tests/RunCMake/install/DIRECTORY-symlink-clobber-build/root-all/dest/lnk/file
+-- Installing: [^
+]*/Tests/RunCMake/install/DIRECTORY-symlink-clobber-build/root-all/dest/dir

Tests/RunCMake/install/DIRECTORY-symlink-clobber.cmake

@@ -0,0 +1,11 @@
+file(MAKE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/old/dir)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/old/dir/file "")
+file(CREATE_LINK dir ${CMAKE_CURRENT_BINARY_DIR}/old/lnk SYMBOLIC)
+install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/old/dir DESTINATION dest)
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/old/lnk     DESTINATION dest)
+
+file(MAKE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/new/lnk)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/new/lnk/file "")
+file(CREATE_LINK lnk ${CMAKE_CURRENT_BINARY_DIR}/new/dir SYMBOLIC)
+install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/new/lnk DESTINATION dest)
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/new/dir     DESTINATION dest)

Tests/RunCMake/install/RunCMakeTest.cmake

@@ -175,6 +175,10 @@ run_install_test(FILES-PERMISSIONS)
 run_install_test(TARGETS-RPATH)
 run_install_test(InstallRequiredSystemLibraries)
 
+if(UNIX)
+  run_install_test(DIRECTORY-symlink-clobber)
+endif()
+
 if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
   run_cmake(TARGETS-RUNTIME_DEPENDENCIES-macos-two-bundle)
   run_cmake(TARGETS-RUNTIME_DEPENDENCIES-macos-no-framework)