Computed roots: extend data structure to support the absent pragma

4 files changed, 49 insertions, 13 deletions

diff --git a/share/man/just-repository-config.5.md b/share/man/just-repository-config.5.md
index 9d038641..ca272ea4 100644
--- a/share/man/just-repository-config.5.md
+++ b/share/man/just-repository-config.5.md
@@ -37,10 +37,14 @@ which determines the type and semantic of the subsequent elements:
       entry is missing, the root is considered absent and any target
       requiring this root has to come from a specified serve end point.
 
- - *`"computed"`* refers to a file root that is the result of evaluating
-   an export target of a content-fixed repository. The list has to have
-   length 5, with the remaining arguments being the global repository name,
-   the module name, the target name, and the configuration, in that order.
+ - *`"computed"`* refers to a file root that is the result of
+   evaluating an export target of a content-fixed repository. The
+   list has to have length 5 or 6, with the remaining arguments
+   being the global repository name, the module name, the target
+   name, and the configuration, in that order, optionally followed
+   by a pragma object. If the pragma object contains the entry
+   `true` for the key `"absent"`, that root is considered absent,
+   otherwise not.
 
  - *`"tree structure"`* refers to the directory structure of a file root.
    The list has to have length 2 or 3. The second argument contains the
diff --git a/src/buildtool/file_system/precomputed_root.cpp b/src/buildtool/file_system/precomputed_root.cpp
index 0ff02628..73d99ef1 100644
--- a/src/buildtool/file_system/precomputed_root.cpp
+++ b/src/buildtool/file_system/precomputed_root.cpp
@@ -51,10 +51,12 @@ template <typename T>
 template <>
 [[nodiscard]] auto ParseImpl<ComputedRoot>(nlohmann::json const& root)
     -> expected<ComputedRoot, std::string> {
-    if (root.size() != ComputedRoot::kSchemeLength) {
+    if ((root.size() != ComputedRoot::kSchemeLength) and
+        (root.size() != ComputedRoot::kSchemeLength + 1)) {
         return unexpected{fmt::format(
             "The root has a wrong number of arguments: {}\nThe scheme requires "
-            "[<scheme>, <root>, <module>, <name>, <config>]",
+            "[<scheme>, <root>, <module>, <name>, <config>] optionally "
+            "followed by a pragma object",
             root.dump())};
     }
 
@@ -77,14 +79,37 @@ template <>
     if (not root[4].is_object()) {
         return unexpected{
             fmt::format("The root has a wrong type of <config>. Expected a "
-                        "plain json, got {}",
+                        "plain json object, got {}",
                         root[4].dump())};
     }
 
+    auto absent = false;
+
+    if (root.size() > ComputedRoot::kSchemeLength) {
+        if (not root[ComputedRoot::kSchemeLength].is_object()) {
+            return unexpected{
+                fmt::format("The root has a wrong type of optional pragma "
+                            "argument. Expected a "
+                            "plain json object, got {}",
+                            root[ComputedRoot::kSchemeLength].dump())};
+        }
+        if (root[ComputedRoot::kSchemeLength].contains("absent")) {
+            auto absent_entry = root[ComputedRoot::kSchemeLength]["absent"];
+            if (not absent_entry.is_boolean()) {
+                return unexpected{
+                    fmt::format("Expected pragma entry \"absent\" to be "
+                                "boolean, but found {}",
+                                absent_entry.dump())};
+            }
+            absent = absent_entry;
+        }
+    }
+
     return ComputedRoot{.repository = std::string{root[1]},
                         .target_module = std::string{root[2]},
                         .target_name = std::string{root[3]},
-                        .config = root[4]};
+                        .config = root[4],
+                        .absent = absent};
 }
 
 template <>
@@ -135,7 +160,8 @@ auto ComputedRoot::operator==(ComputedRoot const& other) const noexcept
     -> bool {
     return repository == other.repository and
            target_module == other.target_module and
-           target_name == other.target_name and config == other.config;
+           target_name == other.target_name and config == other.config and
+           absent == other.absent;
 }
 
 auto ComputedRoot::operator<(ComputedRoot const& other) const noexcept -> bool {
@@ -148,14 +174,18 @@ auto ComputedRoot::operator<(ComputedRoot const& other) const noexcept -> bool {
     if (auto const res = target_name <=> other.target_name; res != 0) {
         return res < 0;
     }
+    if (absent != other.absent) {
+        return absent;
+    }
     return config < other.config;
 }
 
 auto ComputedRoot::ToString() const -> std::string {
-    return fmt::format("([\"@\", {}, {}, {}], {})",
+    return fmt::format("([\"@\", {}, {}, {}{}], {})",
                        nlohmann::json(repository).dump(),
                        nlohmann::json(target_module).dump(),
                        nlohmann::json(target_name).dump(),
+                       absent ? ", {\"absent\": true}" : "",
                        config.dump());
 }
 
@@ -165,6 +195,7 @@ auto ComputedRoot::ComputeHash() const -> std::size_t {
     hash_combine<std::string>(&seed, repository);
     hash_combine<std::string>(&seed, target_module);
     hash_combine<std::string>(&seed, target_name);
+    hash_combine<bool>(&seed, absent);
     hash_combine<nlohmann::json>(&seed, config);
     return seed;
 }
diff --git a/src/buildtool/file_system/precomputed_root.hpp b/src/buildtool/file_system/precomputed_root.hpp
index f3495418..f95f7d73 100644
--- a/src/buildtool/file_system/precomputed_root.hpp
+++ b/src/buildtool/file_system/precomputed_root.hpp
@@ -33,6 +33,7 @@ struct ComputedRoot final {
     std::string target_module;
     std::string target_name;
     nlohmann::json config;
+    bool absent;
 
     [[nodiscard]] auto operator==(ComputedRoot const& other) const noexcept
         -> bool;
diff --git a/src/other_tools/utils/parse_precomputed_root.cpp b/src/other_tools/utils/parse_precomputed_root.cpp
index f30316e6..c5eebf90 100644
--- a/src/other_tools/utils/parse_precomputed_root.cpp
+++ b/src/other_tools/utils/parse_precomputed_root.cpp
@@ -84,9 +84,9 @@ namespace {
     return ComputedRoot{.repository = repo->String(),
                         .target_module = target_module->String(),
                         .target_name = target_module->String(),
-                        .config = config.IsNotNull()
-                                      ? config->ToJson()
-                                      : nlohmann::json::object()};
+                        .config = config.IsNotNull() ? config->ToJson()
+                                                     : nlohmann::json::object(),
+                        .absent = false};
 }
 
 [[nodiscard]] auto ParseTreeStructureRoot(ExpressionPtr const& repository)