cmake: Warn about unnecessary paths on command line

We can't make it an error as that would break existing behavior.

Fixes: #23110

Source/cmake.cxx

@@ -790,6 +790,7 @@ void cmake::SetArgs(const std::vector<std::string>& args)
   bool haveBArg = false;
   bool scriptMode = false;
   std::string possibleUnknownArg;
+  std::string extraProvidedPath;
 #if !defined(CMAKE_BOOTSTRAP)
   std::string profilingFormat;
   std::string profilingOutput;
@@ -1168,10 +1169,18 @@ void cmake::SetArgs(const std::vector<std::string>& args)
     } else if (!matched && cmHasLiteralPrefix(arg, "-")) {
       possibleUnknownArg = arg;
     } else if (!matched) {
-      this->SetDirectoriesFromFile(arg);
+      bool parsedDirectory = this->SetDirectoriesFromFile(arg);
+      if (!parsedDirectory) {
+        extraProvidedPath = arg;
+      }
     }
   }
 
+  if (!extraProvidedPath.empty() && !scriptMode) {
+    this->IssueMessage(MessageType::WARNING,
+                       cmStrCat("Ignoring extra path from command line:\n ",
+                                extraProvidedPath));
+  }
   if (!possibleUnknownArg.empty() && !scriptMode) {
     cmSystemTools::Error(cmStrCat("Unknown argument ", possibleUnknownArg));
     cmSystemTools::Error("Run 'cmake --help' for all supported options.");
@@ -1450,22 +1459,27 @@ void cmake::PrintTraceFormatVersion()
   }
 }
 
-void cmake::SetDirectoriesFromFile(const std::string& arg)
+bool cmake::SetDirectoriesFromFile(const std::string& arg)
 {
   // Check if the argument refers to a CMakeCache.txt or
   // CMakeLists.txt file.
   std::string listPath;
   std::string cachePath;
+  bool is_empty_directory = false;
   if (cmSystemTools::FileIsDirectory(arg)) {
     std::string path = cmSystemTools::CollapseFullPath(arg);
     cmSystemTools::ConvertToUnixSlashes(path);
     std::string cacheFile = cmStrCat(path, "/CMakeCache.txt");
     std::string listFile = cmStrCat(path, "/CMakeLists.txt");
+
+    is_empty_directory = true;
     if (cmSystemTools::FileExists(cacheFile)) {
       cachePath = path;
+      is_empty_directory = false;
     }
     if (cmSystemTools::FileExists(listFile)) {
       listPath = path;
+      is_empty_directory = false;
     }
   } else if (cmSystemTools::FileExists(arg)) {
     std::string fullPath = cmSystemTools::CollapseFullPath(arg);
@@ -1497,7 +1511,7 @@ void cmake::SetDirectoriesFromFile(const std::string& arg)
       if (existingValue) {
         this->SetHomeOutputDirectory(cachePath);
         this->SetHomeDirectory(*existingValue);
-        return;
+        return true;
       }
     }
   }
@@ -1505,9 +1519,15 @@ void cmake::SetDirectoriesFromFile(const std::string& arg)
   bool no_source_tree = this->GetHomeDirectory().empty();
   bool no_build_tree = this->GetHomeOutputDirectory().empty();
 
+  // When invoked with a path that points to an existing CMakeCache
+  // This function is called multiple times with the same path
+  const bool passed_same_path = (listPath == this->GetHomeDirectory()) ||
+    (listPath == this->GetHomeOutputDirectory());
+  bool used_provided_path =
+    (passed_same_path || no_source_tree || no_build_tree);
+
   // If there is a CMakeLists.txt file, use it as the source tree.
   if (!listPath.empty()) {
-
     // When invoked with a path that points to an existing CMakeCache
     // This function is called multiple times with the same path
     if (no_source_tree && no_build_tree) {
@@ -1527,13 +1547,20 @@ void cmake::SetDirectoriesFromFile(const std::string& arg)
       std::string full = cmSystemTools::CollapseFullPath(arg);
       this->SetHomeDirectory(full);
     }
-    if (no_build_tree) {
+    if (no_build_tree && !no_source_tree && is_empty_directory) {
+      // passed `-S <path> <build_dir> when build_dir is an empty directory
+      std::string full = cmSystemTools::CollapseFullPath(arg);
+      this->SetHomeOutputDirectory(full);
+    } else if (no_build_tree) {
       // We didn't find a CMakeCache.txt and it wasn't specified
       // with -B. Assume the current working directory as the build tree.
       std::string cwd = cmSystemTools::GetCurrentWorkingDirectory();
       this->SetHomeOutputDirectory(cwd);
+      used_provided_path = false;
     }
   }
+
+  return used_provided_path;
 }
 
 // at the end of this CMAKE_ROOT and CMAKE_COMMAND should be added to the

Source/cmake.h

@@ -648,7 +648,7 @@ protected:
    */
   int CheckBuildSystem();
 
-  void SetDirectoriesFromFile(const std::string& arg);
+  bool SetDirectoriesFromFile(const std::string& arg);
 
   //! Make sure all commands are what they say they are and there is no
   /// macros.

Tests/RunCMake/CommandLine/B-S-extra-path-stderr.txt

@@ -0,0 +1,4 @@
+^CMake Warning:
+  Ignoring extra path from command line:
+
+   /extra/path/$

Tests/RunCMake/CommandLine/RunCMakeTest.cmake

@@ -143,6 +143,10 @@ endif()
   run_cmake_with_options(S-arg-build-dir-not-created -S ${source_dir} build/)
   run_cmake_with_options(S-arg-reverse-build-dir-not-created build/ -S${source_dir} )
 
+  file(REMOVE_RECURSE "${source_dir}/build")
+  file(MAKE_DIRECTORY "${source_dir}/build")
+  run_cmake_with_options(S-arg-build-dir-empty -S ${source_dir} build/)
+
   set(source_dir ${RunCMake_SOURCE_DIR}/ExplicitDirs)
   set(binary_dir ${RunCMake_BINARY_DIR}/ExplicitDirs-build)
 
@@ -155,6 +159,7 @@ endif()
   run_cmake_with_options(S-no-arg -S )
   run_cmake_with_options(S-no-arg2 -S -T)
   run_cmake_with_options(S-B -S ${source_dir} -B ${binary_dir})
+  run_cmake_with_options(S-B-extra-path -S ${source_dir} -B ${binary_dir} /extra/path/)
 
   # make sure that -B can explicitly construct build directories
   file(REMOVE_RECURSE "${binary_dir}")
@@ -165,6 +170,7 @@ endif()
   run_cmake_with_options(B-no-arg2 -B -T)
   file(REMOVE_RECURSE "${binary_dir}")
   run_cmake_with_options(B-S -B${binary_dir} -S${source_dir})
+  run_cmake_with_options(B-S-extra-path -B${binary_dir} -S${source_dir} /extra/path/)
 
   message("copied to ${RunCMake_TEST_BINARY_DIR}/initial-cache.txt")
   file(COPY ${RunCMake_SOURCE_DIR}/C_buildsrcdir/initial-cache.txt DESTINATION ${RunCMake_TEST_BINARY_DIR})

Tests/RunCMake/CommandLine/S-B-extra-path-stderr.txt

@@ -0,0 +1,4 @@
+^CMake Warning:
+  Ignoring extra path from command line:
+
+   /extra/path/$