cmake: Improve '-E create_symlink' edge case handling (#14713)

The logic added by commit ffc0b5e4 (Overwrite the symlink if it already
exists, 2007-02-15) does not recognize and remove existing broken links
before replacing them.  Improve the logic to remove any existing
destination file or link (but not directory).  On failure, report an
error message explaining why the existing path could not be removed or
the new one could not be created.

Add a RunCMake.CommandLine test to cover 'cmake -E' cases.  Start with
test cases covering 'cmake -E create_symlink' behavior on UNIX platforms.

9 files changed, 56 insertions, 15 deletions

diff --git a/Source/cmcmd.cxx b/Source/cmcmd.cxx
index 7891969..c1576c4 100644
--- a/Source/cmcmd.cxx
+++ b/Source/cmcmd.cxx
@@ -460,23 +460,25 @@ int cmcmd::ExecuteCMakeCommand(std::vector<std::string>& args)
     else if (args[1] == "create_symlink" && args.size() == 4)
       {
       const char* destinationFileName = args[3].c_str();
-      if ( cmSystemTools::FileExists(destinationFileName) )
+      if((cmSystemTools::FileExists(destinationFileName) ||
+          cmSystemTools::FileIsSymlink(destinationFileName)) &&
+         !cmSystemTools::RemoveFile(destinationFileName))
         {
-        if ( cmSystemTools::FileIsSymlink(destinationFileName) )
-          {
-          if ( !cmSystemTools::RemoveFile(destinationFileName) ||
-            cmSystemTools::FileExists(destinationFileName) )
-            {
-            return 0;
-            }
-          }
-        else
-          {
-          return 0;
-          }
+        std::string emsg = cmSystemTools::GetLastSystemError();
+        std::cerr <<
+          "failed to create symbolic link '" << destinationFileName <<
+          "' because existing path cannot be removed: " << emsg << "\n";
+        return 1;
+        }
+      if(!cmSystemTools::CreateSymlink(args[2].c_str(), args[3].c_str()))
+        {
+        std::string emsg = cmSystemTools::GetLastSystemError();
+        std::cerr <<
+          "failed to create symbolic link '" << destinationFileName <<
+          "': " << emsg << "\n";
+        return 1;
         }
-      return cmSystemTools::CreateSymlink(args[2].c_str(),
-                                          args[3].c_str())? 0:1;
+      return 0;
       }
 
     // Internal CMake shared library support.
diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index fc730a7..9646e67 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -111,5 +111,6 @@ add_RunCMake_test(File_Generate)
 add_RunCMake_test(ExportWithoutLanguage)
 add_RunCMake_test(target_link_libraries)
 add_RunCMake_test(CheckModules)
+add_RunCMake_test(CommandLine)
 
 add_RunCMake_test(install)
diff --git a/Tests/RunCMake/CommandLine/E_create_symlink-broken-create-check.cmake b/Tests/RunCMake/CommandLine/E_create_symlink-broken-create-check.cmake
new file mode 100644
index 0000000..d7e652d
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/E_create_symlink-broken-create-check.cmake
@@ -0,0 +1,6 @@
+if(NOT IS_SYMLINK ${RunCMake_TEST_BINARY_DIR}/L)
+  set(RunCMake_TEST_FAILED "Symlink 'L' incorrectly not created!")
+endif()
+if(EXISTS ${RunCMake_TEST_BINARY_DIR}/L)
+  set(RunCMake_TEST_FAILED "Symlink 'L' not broken!")
+endif()
diff --git a/Tests/RunCMake/CommandLine/E_create_symlink-broken-replace-check.cmake b/Tests/RunCMake/CommandLine/E_create_symlink-broken-replace-check.cmake
new file mode 100644
index 0000000..c078ae8
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/E_create_symlink-broken-replace-check.cmake
@@ -0,0 +1,3 @@
+if(NOT IS_DIRECTORY ${RunCMake_TEST_BINARY_DIR}/L)
+  set(RunCMake_TEST_FAILED "Symlink 'L' not replaced correctly!")
+endif()
diff --git a/Tests/RunCMake/CommandLine/E_create_symlink-missing-dir-result.txt b/Tests/RunCMake/CommandLine/E_create_symlink-missing-dir-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/E_create_symlink-missing-dir-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/CommandLine/E_create_symlink-missing-dir-stderr.txt b/Tests/RunCMake/CommandLine/E_create_symlink-missing-dir-stderr.txt
new file mode 100644
index 0000000..7a6d84b
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/E_create_symlink-missing-dir-stderr.txt
@@ -0,0 +1 @@
+failed to create symbolic link 'missing-dir/L':
diff --git a/Tests/RunCMake/CommandLine/E_create_symlink-no-replace-dir-result.txt b/Tests/RunCMake/CommandLine/E_create_symlink-no-replace-dir-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/E_create_symlink-no-replace-dir-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/CommandLine/E_create_symlink-no-replace-dir-stderr.txt b/Tests/RunCMake/CommandLine/E_create_symlink-no-replace-dir-stderr.txt
new file mode 100644
index 0000000..ebed0d6
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/E_create_symlink-no-replace-dir-stderr.txt
@@ -0,0 +1 @@
+failed to create symbolic link '\.' because existing path cannot be removed:
diff --git a/Tests/RunCMake/CommandLine/RunCMakeTest.cmake b/Tests/RunCMake/CommandLine/RunCMakeTest.cmake
new file mode 100644
index 0000000..ee6cd99
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/RunCMakeTest.cmake
@@ -0,0 +1,25 @@
+include(RunCMake)
+
+if(UNIX)
+  run_cmake_command(E_create_symlink-missing-dir
+    ${CMAKE_COMMAND} -E create_symlink T missing-dir/L
+    )
+
+  # Use a single build tree for a few tests without cleaning.
+  set(RunCMake_TEST_BINARY_DIR
+    ${RunCMake_BINARY_DIR}/E_create_symlink-broken-build)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  run_cmake_command(E_create_symlink-broken-create
+    ${CMAKE_COMMAND} -E create_symlink T L
+    )
+  run_cmake_command(E_create_symlink-broken-replace
+    ${CMAKE_COMMAND} -E create_symlink . L
+    )
+  unset(RunCMake_TEST_BINARY_DIR)
+  unset(RunCMake_TEST_NO_CLEAN)
+
+  run_cmake_command(E_create_symlink-no-replace-dir
+    ${CMAKE_COMMAND} -E create_symlink T .
+    )
+endif()