find_*: Avoid searching prefix derived from CMake's own source tree

When `cmake` is running from its own build tree, `CMAKE_ROOT` is in
the source tree and should not be used to derive a search prefix.

Fixes: #27853

Modules/Platform/CrayLinuxEnvironment.cmake

@@ -40,9 +40,16 @@ endif()
 # The rest of this file is based on UnixPaths.cmake, adjusted for Cray
 
 # add the install directory of the running cmake to the search directories
-# CMAKE_ROOT is CMAKE_INSTALL_PREFIX/share/cmake, so we need to go two levels up
+# CMAKE_ROOT is CMAKE_INSTALL_PREFIX/share/cmake, so we need to go two levels up.
+# When CMake runs from its build tree, CMAKE_ROOT is the source tree instead.
 get_filename_component(__cmake_install_dir "${CMAKE_ROOT}" PATH)
 get_filename_component(__cmake_install_dir "${__cmake_install_dir}" PATH)
+get_property(__cmake_running_in_build_tree GLOBAL PROPERTY
+  _CMAKE_RUNNING_IN_BUILD_TREE)
+if(__cmake_running_in_build_tree)
+  set(__cmake_install_dir "")
+endif()
+unset(__cmake_running_in_build_tree)
 
 # Note: Some Cray's have the SYSROOT_DIR variable defined, pointing to a copy
 # of the NIDs userland.  If so, then we'll use it.  Otherwise, just assume
@@ -53,10 +60,13 @@ get_filename_component(__cmake_install_dir "${__cmake_install_dir}" PATH)
 list(APPEND CMAKE_SYSTEM_PREFIX_PATH
   # Standard
   $ENV{SYSROOT_DIR}/usr/local $ENV{SYSROOT_DIR}/usr $ENV{SYSROOT_DIR}/
-
-  # CMake install location
-  "${__cmake_install_dir}"
   )
+if(__cmake_install_dir)
+  list(APPEND CMAKE_SYSTEM_PREFIX_PATH
+    # CMake install location
+    "${__cmake_install_dir}"
+    )
+endif()
 if (NOT CMAKE_FIND_NO_INSTALL_PREFIX)
   list(APPEND CMAKE_SYSTEM_PREFIX_PATH
     # Project install destination.

Modules/Platform/UnixPaths.cmake

@@ -18,9 +18,16 @@ set(__UNIX_PATHS_INCLUDED 1)
 set(UNIX 1)
 
 # also add the install directory of the running cmake to the search directories
-# CMAKE_ROOT is CMAKE_INSTALL_PREFIX/share/cmake, so we need to go two levels up
+# CMAKE_ROOT is CMAKE_INSTALL_PREFIX/share/cmake, so we need to go two levels up.
+# When CMake runs from its build tree, CMAKE_ROOT is the source tree instead.
 get_filename_component(_CMAKE_INSTALL_DIR "${CMAKE_ROOT}" PATH)
 get_filename_component(_CMAKE_INSTALL_DIR "${_CMAKE_INSTALL_DIR}" PATH)
+get_property(_cmake_running_in_build_tree GLOBAL PROPERTY
+  _CMAKE_RUNNING_IN_BUILD_TREE)
+if(_cmake_running_in_build_tree)
+  set(_CMAKE_INSTALL_DIR "")
+endif()
+unset(_cmake_running_in_build_tree)
 
 # List common installation prefixes.  These will be used for all
 # search types.
@@ -31,10 +38,13 @@ get_filename_component(_CMAKE_INSTALL_DIR "${_CMAKE_INSTALL_DIR}" PATH)
 list(APPEND CMAKE_SYSTEM_PREFIX_PATH
   # Standard
   /usr/local /usr /
-
-  # CMake install location
-  "${_CMAKE_INSTALL_DIR}"
   )
+if(_CMAKE_INSTALL_DIR)
+  list(APPEND CMAKE_SYSTEM_PREFIX_PATH
+    # CMake install location
+    "${_CMAKE_INSTALL_DIR}"
+    )
+endif()
 if (NOT CMAKE_FIND_NO_INSTALL_PREFIX)
   list(APPEND CMAKE_SYSTEM_PREFIX_PATH
     # Project install destination.

Modules/Platform/WindowsPaths.cmake

@@ -50,9 +50,19 @@ endif()
 unset(_programfiles)
 
 # Add the CMake install location.
+# CMAKE_ROOT is CMAKE_INSTALL_PREFIX/share/cmake, so we need to go two levels up.
+# When CMake runs from its build tree, CMAKE_ROOT is the source tree instead.
 get_filename_component(_CMAKE_INSTALL_DIR "${CMAKE_ROOT}" PATH)
 get_filename_component(_CMAKE_INSTALL_DIR "${_CMAKE_INSTALL_DIR}" PATH)
-list(APPEND CMAKE_SYSTEM_PREFIX_PATH "${_CMAKE_INSTALL_DIR}")
+get_property(_cmake_running_in_build_tree GLOBAL PROPERTY
+  _CMAKE_RUNNING_IN_BUILD_TREE)
+if(_cmake_running_in_build_tree)
+  set(_CMAKE_INSTALL_DIR "")
+endif()
+unset(_cmake_running_in_build_tree)
+if(_CMAKE_INSTALL_DIR)
+  list(APPEND CMAKE_SYSTEM_PREFIX_PATH "${_CMAKE_INSTALL_DIR}")
+endif()
 
 if (NOT CMAKE_FIND_NO_INSTALL_PREFIX)
   # Add other locations.
@@ -88,8 +98,12 @@ if (NOT CMAKE_FIND_NO_INSTALL_PREFIX)
     )
   endif()
 endif()
+if(_CMAKE_INSTALL_DIR)
+  list(APPEND CMAKE_SYSTEM_LIBRARY_PATH
+    "${_CMAKE_INSTALL_DIR}/bin"
+    )
+endif()
 list(APPEND CMAKE_SYSTEM_LIBRARY_PATH
-  "${_CMAKE_INSTALL_DIR}/bin"
   /bin
   )
 

Source/cmState.cxx

@@ -673,6 +673,9 @@ cmValue cmState::GetGlobalProperty(std::string const& prop)
     this->SetGlobalProperty("ENABLED_LANGUAGES", langs);
   } else if (prop == "CMAKE_ROLE") {
     this->SetGlobalProperty("CMAKE_ROLE", this->GetRoleString());
+  } else if (prop == "_CMAKE_RUNNING_IN_BUILD_TREE") {
+    this->SetGlobalProperty("_CMAKE_RUNNING_IN_BUILD_TREE",
+                            cmSystemTools::GetCMakeInBuildTree() ? "1" : "0");
   }
 #define STRING_LIST_ELEMENT(F) ";" #F
   if (prop == "CMAKE_C_KNOWN_FEATURES") {

Source/cmSystemTools.cxx

@@ -2889,6 +2889,8 @@ std::string InitLogicalWorkingDirectory()
   return cwd;
 }
 
+bool cmSystemToolsCMakeInBuildTree = false;
+
 std::string cmSystemToolsLogicalWorkingDirectory =
   InitLogicalWorkingDirectory();
 
@@ -3013,6 +3015,7 @@ void FindCMakeResourcesInBuildTree(std::string const& exe_dir)
   if (fin && cmSystemTools::GetLineFromStream(fin, src_dir) &&
       cmSystemTools::FileIsDirectory(src_dir)) {
     cmSystemToolsCMakeRoot = src_dir;
+    cmSystemToolsCMakeInBuildTree = true;
   } else {
     dir = cmSystemTools::GetFilenamePath(dir);
     src_dir_txt = cmStrCat(dir, "/CMakeFiles/CMakeSourceDir.txt");
@@ -3020,6 +3023,7 @@ void FindCMakeResourcesInBuildTree(std::string const& exe_dir)
     if (fin2 && cmSystemTools::GetLineFromStream(fin2, src_dir) &&
         cmSystemTools::FileIsDirectory(src_dir)) {
       cmSystemToolsCMakeRoot = src_dir;
+      cmSystemToolsCMakeInBuildTree = true;
     }
   }
   if (!cmSystemToolsCMakeRoot.empty() && cmSystemToolsHTMLDoc.empty() &&
@@ -3037,6 +3041,7 @@ void cmSystemTools::FindCMakeResources(char const* argv0)
 #ifdef CMAKE_BOOTSTRAP
   // The bootstrap cmake knows its resource locations.
   cmSystemToolsCMakeRoot = CMAKE_BOOTSTRAP_SOURCE_DIR;
+  cmSystemToolsCMakeInBuildTree = true;
   cmSystemToolsCMakeCommand = exe;
   // The bootstrap cmake does not provide the other tools,
   // so use the directory where they are about to be built.
@@ -3120,6 +3125,11 @@ std::string const& cmSystemTools::GetCMakeRoot()
   return cmSystemToolsCMakeRoot;
 }
 
+bool cmSystemTools::GetCMakeInBuildTree()
+{
+  return cmSystemToolsCMakeInBuildTree;
+}
+
 std::string const& cmSystemTools::GetHTMLDoc()
 {
   return cmSystemToolsHTMLDoc;

Source/cmSystemTools.h

@@ -560,6 +560,7 @@ public:
   static std::string const& GetCMakeCursesCommand();
   static std::string const& GetCMClDepsCommand();
   static std::string const& GetCMakeRoot();
+  static bool GetCMakeInBuildTree();
   static std::string const& GetHTMLDoc();
 
   /** Get the CMake config directory **/

Tests/RunCMake/find_library/BuildTreePrefixNoLeak.cmake

@@ -0,0 +1,32 @@
+# Regression net for the build-tree prefix leak fixed in the Platform modules.
+# When CMake runs from its build tree, CMAKE_ROOT is the source tree rather
+# than an install-tree resource directory.  In that case, the historical
+# dirname(dirname(CMAKE_ROOT)) install-prefix calculation must not be added to
+# CMAKE_SYSTEM_PREFIX_PATH.
+
+get_property(_cmake_running_in_build_tree GLOBAL PROPERTY
+  _CMAKE_RUNNING_IN_BUILD_TREE)
+
+if(_cmake_running_in_build_tree)
+  get_filename_component(_leak_root_dir "${CMAKE_ROOT}" PATH)
+  get_filename_component(_leak_prefix "${_leak_root_dir}" PATH)
+
+    # Empty means there is no candidate.  "/" is already a standard entry, not
+    # evidence of this leak.
+    if(_leak_prefix AND
+      NOT _leak_prefix STREQUAL "/" AND
+      _leak_prefix IN_LIST CMAKE_SYSTEM_PREFIX_PATH)
+    # Corner case intentionally not excluded: checking the CMake *source* tree
+    # out into a system prefix such as /usr/src or /opt/<x> would make
+    # _leak_prefix a standard root and trip this assertion.  Those are
+    # install/system trees, not dev/CI workspaces, so the corner is treated as
+    # an unsupported layout.
+    message(FATAL_ERROR
+      "CMAKE_SYSTEM_PREFIX_PATH leaked dirname(dirname(CMAKE_ROOT))=\"${_leak_prefix}\" "
+      "(CMAKE_ROOT=\"${CMAKE_ROOT}\"); the Platform/*.cmake build-tree guard regressed.")
+  endif()
+endif()
+
+unset(_cmake_running_in_build_tree)
+unset(_leak_root_dir)
+unset(_leak_prefix)

Tests/RunCMake/find_library/RunCMakeTest.cmake

@@ -3,6 +3,7 @@ include(RunCMake)
 run_cmake(ConfigureLogTransitions)
 run_cmake(ConfigureLogTransitionsSuppressed)
 run_cmake(Created)
+run_cmake(BuildTreePrefixNoLeak)
 run_cmake(FromPrefixPath)
 run_cmake(FromPATHEnv)
 run_cmake_with_options(IgnoreInstallPrefix "-DCMAKE_INSTALL_PREFIX=${RunCMake_BINARY_DIR}/IgnoreInstallPrefix-build/")