built-in "install" rule: verify well-formedness of resulting stage

The install target, like any other target, has to have artifacts
and runfiles being proper stages, i.e., in such a way that the
keys can be interpreted as names in the file system without causing
conflicts. This property used to be unchecked, thus allowing users
to define mal-formed targets that, when used as inputs to actions,
would result in unspecified layout of the action directory. Fix
this by adding an appropriate check enforcing well-formedness of
the resulting stage.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/buildtool/build_engine/target_map/built_in_rules.cpp b/src/buildtool/build_engine/target_map/built_in_rules.cpp
index 6bd65a55..70ecf1f2 100644
--- a/src/buildtool/build_engine/target_map/built_in_rules.cpp
+++ b/src/buildtool/build_engine/target_map/built_in_rules.cpp
@@ -666,6 +666,11 @@ void InstallRuleWithDeps(
         stage = ExpressionPtr{Expression::map_t{stage, to_stage}};
     }
 
+    auto conflict = BuildMaps::Target::Utils::tree_conflict(stage);
+    if (conflict) {
+        (*logger)(fmt::format("TREE conflict on subtree {}", *conflict), true);
+        return;
+    }
     auto const& empty_map = Expression::kEmptyMap;
     auto result = std::make_shared<AnalysedTarget const>(
         TargetResult{