From 25b6e7b710d7739cca44ed19bf45a190e72a6b82 Mon Sep 17 00:00:00 2001
From: Brad King <brad.king@kitware.com>
Date: Thu, 17 Nov 2016 10:29:55 -0500
Subject: Tolerate removed/replaced CMakeCache.txt with old CMakeFiles/

Users or scripts commonly remove or replace `CMakeCache.txt` without
also removing `CMakeFiles/`.  In this case the information saved in the
cache from platform information initialization is missing, so we need to
re-initialize it.  In such a case, remove the platform information
directory so that re-initialization will occur and restore needed
information to the cache.

Closes: #14820
---
 Source/cmGlobalGenerator.cxx                    | 20 ++++++++++++++++++++
 Tests/RunCMake/Configure/RemoveCache-stdout.txt |  1 +
 Tests/RunCMake/Configure/RemoveCache.cmake      | 17 +++++++++++++++++
 Tests/RunCMake/Configure/RunCMakeTest.cmake     |  9 +++++++++
 4 files changed, 47 insertions(+)
 create mode 100644 Tests/RunCMake/Configure/RemoveCache-stdout.txt
 create mode 100644 Tests/RunCMake/Configure/RemoveCache.cmake

diff --git a/Source/cmGlobalGenerator.cxx b/Source/cmGlobalGenerator.cxx
index fa447ff..2808051 100644
--- a/Source/cmGlobalGenerator.cxx
+++ b/Source/cmGlobalGenerator.cxx
@@ -50,6 +50,9 @@
 #include <cm_jsoncpp_writer.h>
 #endif
 
+const std::string kCMAKE_PLATFORM_INFO_INITIALIZED =
+  "CMAKE_PLATFORM_INFO_INITIALIZED";
+
 class cmInstalledFile;
 
 bool cmTarget::StrictTargetComparison::operator()(cmTarget const* t1,
@@ -428,6 +431,23 @@ void cmGlobalGenerator::EnableLanguage(
   // set the dir for parent files so they can be used by modules
   mf->AddDefinition("CMAKE_PLATFORM_INFO_DIR", rootBin.c_str());
 
+  if (!this->CMakeInstance->GetIsInTryCompile()) {
+    // Keep a mark in the cache to indicate that we've initialized the
+    // platform information directory.  If the platform information
+    // directory exists but the mark is missing then CMakeCache.txt
+    // has been removed or replaced without also removing the CMakeFiles/
+    // directory.  In this case remove the platform information directory
+    // so that it will be re-initialized and the relevant information
+    // restored in the cache.
+    if (cmSystemTools::FileIsDirectory(rootBin) &&
+        !mf->IsOn(kCMAKE_PLATFORM_INFO_INITIALIZED)) {
+      cmSystemTools::RemoveADirectory(rootBin);
+    }
+    this->GetCMakeInstance()->AddCacheEntry(
+      kCMAKE_PLATFORM_INFO_INITIALIZED, "1",
+      "Platform information initialized", cmStateEnums::INTERNAL);
+  }
+
   // find and make sure CMAKE_MAKE_PROGRAM is defined
   if (!this->FindMakeProgram(mf)) {
     return;
diff --git a/Tests/RunCMake/Configure/RemoveCache-stdout.txt b/Tests/RunCMake/Configure/RemoveCache-stdout.txt
new file mode 100644
index 0000000..73e7e5d
--- /dev/null
+++ b/Tests/RunCMake/Configure/RemoveCache-stdout.txt
@@ -0,0 +1 @@
+-- The C compiler identification is
diff --git a/Tests/RunCMake/Configure/RemoveCache.cmake b/Tests/RunCMake/Configure/RemoveCache.cmake
new file mode 100644
index 0000000..304918f
--- /dev/null
+++ b/Tests/RunCMake/Configure/RemoveCache.cmake
@@ -0,0 +1,17 @@
+enable_language(C)
+
+set(vars
+  CMAKE_EXECUTABLE_FORMAT
+  )
+
+if(CMAKE_HOST_UNIX)
+  list(APPEND vars
+    CMAKE_UNAME
+    )
+endif()
+
+foreach(v IN LISTS vars)
+  if(NOT DEFINED ${v})
+    message(SEND_ERROR "Variable '${v}' is not set!")
+  endif()
+endforeach()
diff --git a/Tests/RunCMake/Configure/RunCMakeTest.cmake b/Tests/RunCMake/Configure/RunCMakeTest.cmake
index 91adb4e..4a135be 100644
--- a/Tests/RunCMake/Configure/RunCMakeTest.cmake
+++ b/Tests/RunCMake/Configure/RunCMakeTest.cmake
@@ -24,3 +24,12 @@ file(WRITE "${depend}" "2")
 run_cmake_command(RerunCMake-build2 ${CMAKE_COMMAND} --build .)
 unset(RunCMake_TEST_BINARY_DIR)
 unset(RunCMake_TEST_NO_CLEAN)
+
+# Use a single build tree for a few tests without cleaning.
+set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/RemoveCache-build)
+set(RunCMake_TEST_NO_CLEAN 1)
+file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+run_cmake(RemoveCache)
+file(REMOVE "${RunCMake_TEST_BINARY_DIR}/CMakeCache.txt")
+run_cmake(RemoveCache)
-- 
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