cmake: Allow CMAKE_TOOLCHAIN_FILE to be set by environment variable

When no `CMAKE_TOOLCHAIN_FILE` is explicitly specified while creating
a new build tree, check for an environment variable of the same name.

1 files changed, 10 insertions, 0 deletions

diff --git a/Source/cmake.cxx b/Source/cmake.cxx
index 840a9d959c..9a866ab89b 100644
--- a/Source/cmake.cxx
+++ b/Source/cmake.cxx
@@ -2040,6 +2040,16 @@ int cmake::ActualConfigure()
                         this->GlobalGenerator->GetExtraGeneratorName().c_str(),
                         "Name of external makefile project generator.",
                         cmStateEnums::INTERNAL);
+
+    if (!this->State->GetInitializedCacheValue("CMAKE_TOOLCHAIN_FILE")) {
+      std::string envToolchain;
+      if (cmSystemTools::GetEnv("CMAKE_TOOLCHAIN_FILE", envToolchain) &&
+          !envToolchain.empty()) {
+        this->AddCacheEntry("CMAKE_TOOLCHAIN_FILE", envToolchain.c_str(),
+                            "The CMake toolchain file",
+                            cmStateEnums::FILEPATH);
+      }
+    }
   }
 
   if (cmProp instance =