find_package: Save/restore PACKAGE_PREFIX_DIR

Package configuration files generated by `configure_package_config_file`
set this variable in `@PACKAGE_INIT@` and then use it later.  There may
be intervening calls to `find_package`, e.g., via `find_dependency`.
If the loaded package also used `configure_package_config_file`, it
may change the value of `PACKAGE_PREFIX_DIR`.  Explicitly save and
restore the value to avoid this.

Fixes: #25827

1 files changed, 30 insertions, 0 deletions

diff --git a/Source/cmFindPackageCommand.cxx b/Source/cmFindPackageCommand.cxx
index 9b51b1a..3bfabd9 100644
--- a/Source/cmFindPackageCommand.cxx
+++ b/Source/cmFindPackageCommand.cxx
@@ -982,6 +982,36 @@ bool cmFindPackageCommand::InitialPass(std::vector<std::string> const& args)
     return true;
   }
 
+  // Restore PACKAGE_PREFIX_DIR to its pre-call value when we return. If our
+  // caller is a file generated by configure_package_config_file(), and if
+  // the package we are about to load also has a config file created by that
+  // command, it will overwrite PACKAGE_PREFIX_DIR. We need to restore it in
+  // case something still refers to it in our caller's scope after we return.
+  class RestoreVariableOnLeavingScope
+  {
+    cmMakefile* makefile_;
+    cm::optional<std::string> value_;
+
+  public:
+    RestoreVariableOnLeavingScope(cmMakefile* makefile)
+      : makefile_(makefile)
+    {
+      cmValue v = makefile->GetDefinition("PACKAGE_PREFIX_DIR");
+      if (v) {
+        value_ = *v;
+      }
+    }
+    ~RestoreVariableOnLeavingScope()
+    {
+      if (this->value_) {
+        makefile_->AddDefinition("PACKAGE_PREFIX_DIR", *value_);
+      } else {
+        makefile_->RemoveDefinition("PACKAGE_PREFIX_DIR");
+      }
+    }
+  };
+  RestoreVariableOnLeavingScope restorePackagePrefixDir(this->Makefile);
+
   // Now choose what method(s) we will use to satisfy the request. Note that
   // we still want all the above checking of arguments, etc. regardless of the
   // method used. This will ensure ill-formed arguments are caught earlier,