2 files changed, 44 insertions, 1 deletions
diff --git a/src/other_tools/repo_map/repos_to_setup_map.cpp b/src/other_tools/repo_map/repos_to_setup_map.cpp
index 383f763d..91a69c8b 100644
--- a/src/other_tools/repo_map/repos_to_setup_map.cpp
+++ b/src/other_tools/repo_map/repos_to_setup_map.cpp
@@ -670,6 +670,7 @@ void PrecomputedRootCheckout(ExpressionPtr const& repo_desc,
             auto& ws_root = cfg["workspace_root"];
             SetReposTakeOver(&cfg, repos, repo_name);
 
+            bool absent = false;
             if (auto computed = result.AsComputed()) {
                 ws_root.push_back(ComputedRoot::kMarker);
                 ws_root.push_back(computed->repository);
@@ -680,7 +681,16 @@ void PrecomputedRootCheckout(ExpressionPtr const& repo_desc,
             else if (auto tree_structure = result.AsTreeStructure()) {
                 ws_root.push_back(TreeStructureRoot::kMarker);
                 ws_root.push_back(tree_structure->repository);
+
+                absent = tree_structure->absent;
+            }
+
+            if (absent) {
+                auto pragma = nlohmann::json::object();
+                pragma["absent"] = true;
+                ws_root.push_back(pragma);
             }
+
             std::invoke(*setter, std::move(cfg));
         },
         logger);
diff --git a/src/other_tools/utils/parse_precomputed_root.cpp b/src/other_tools/utils/parse_precomputed_root.cpp
index 7b9ef519..f30316e6 100644
--- a/src/other_tools/utils/parse_precomputed_root.cpp
+++ b/src/other_tools/utils/parse_precomputed_root.cpp
@@ -21,6 +21,34 @@
 #include "src/buildtool/build_engine/expression/expression.hpp"
 
 namespace {
+[[nodiscard]] auto ParseAbsent(ExpressionPtr const& repository)
+    -> expected<bool, std::string> {
+    auto const pragma = repository->Get("pragma", Expression::none_t{});
+    if (not pragma.IsNotNull()) {
+        // Missing "pragma", absent == false
+        return false;
+    }
+
+    if (not pragma->IsMap()) {
+        return unexpected{fmt::format(
+            "Key \"pragma\", if given, should be a map, but found {}",
+            pragma->ToString())};
+    }
+
+    auto const is_absent = pragma->Get("absent", Expression::none_t{});
+    if (not is_absent.IsNotNull()) {
+        // "pragma" doesn't contain "absent", absent == false
+        return false;
+    }
+
+    if (not is_absent->IsBool()) {
+        return unexpected{fmt::format(
+            "Expected pragma \"absent\" to be boolean, but found {}",
+            is_absent->ToString())};
+    }
+    return is_absent->Bool();
+}
+
 [[nodiscard]] auto ParseComputedRoot(ExpressionPtr const& repository)
     -> expected<ComputedRoot, std::string> {
     auto const repo = repository->Get("repo", Expression::none_t{});
@@ -67,7 +95,12 @@ namespace {
     if (not repo.IsNotNull()) {
         return unexpected<std::string>{"Mandatory key \"repo\" is missing"};
     }
-    return TreeStructureRoot{.repository = repo->String(), .absent = false};
+
+    auto absent = ParseAbsent(repository);
+    if (not absent.has_value()) {
+        return unexpected{std::move(absent).error()};
+    }
+    return TreeStructureRoot{.repository = repo->String(), .absent = *absent};
 }
 }  // namespace