1 files changed, 249 insertions, 0 deletions
diff --git a/src/buildtool/build_engine/expression/expression.cpp b/src/buildtool/build_engine/expression/expression.cpp
new file mode 100644
index 00000000..5a161468
--- /dev/null
+++ b/src/buildtool/build_engine/expression/expression.cpp
@@ -0,0 +1,249 @@
+#include "src/buildtool/build_engine/expression/expression.hpp"
+
+#include <exception>
+#include <optional>
+#include <sstream>
+#include <string>
+#include <type_traits>
+
+#include "fmt/core.h"
+#include "gsl-lite/gsl-lite.hpp"
+#include "src/buildtool/build_engine/expression/evaluator.hpp"
+#include "src/buildtool/logging/logger.hpp"
+#include "src/utils/cpp/json.hpp"
+
+auto Expression::operator[](
+    std::string const& key) const& -> ExpressionPtr const& {
+    auto value = Map().Find(key);
+    if (value) {
+        return value->get();
+    }
+    throw ExpressionTypeError{
+        fmt::format("Map does not contain key '{}'.", key)};
+}
+
+auto Expression::operator[](std::string const& key) && -> ExpressionPtr {
+    auto value = std::move(*this).Map().Find(key);
+    if (value) {
+        return std::move(*value);
+    }
+    throw ExpressionTypeError{
+        fmt::format("Map does not contain key '{}'.", key)};
+}
+
+auto Expression::operator[](
+    ExpressionPtr const& key) const& -> ExpressionPtr const& {
+    return (*this)[key->String()];
+}
+
+auto Expression::operator[](ExpressionPtr const& key) && -> ExpressionPtr {
+    return std::move(*this)[key->String()];
+}
+
+auto Expression::operator[](size_t pos) const& -> ExpressionPtr const& {
+    if (pos < List().size()) {
+        return List().at(pos);
+    }
+    throw ExpressionTypeError{
+        fmt::format("List pos '{}' is out of bounds.", pos)};
+}
+
+auto Expression::operator[](size_t pos) && -> ExpressionPtr {
+    auto&& list = std::move(*this).List();
+    if (pos < list.size()) {
+        return list.at(pos);
+    }
+    throw ExpressionTypeError{
+        fmt::format("List pos '{}' is out of bounds.", pos)};
+}
+
+auto Expression::ToJson(Expression::JsonMode mode) const -> nlohmann::json {
+    if (IsBool()) {
+        return Bool();
+    }
+    if (IsNumber()) {
+        return Number();
+    }
+    if (IsString()) {
+        return String();
+    }
+    if (IsArtifact() and mode != JsonMode::NullForNonJson) {
+        return Artifact().ToJson();
+    }
+    if (IsResult() and mode != JsonMode::NullForNonJson) {
+        auto const& result = Result();
+        return Expression{map_t{{{"artifact_stage", result.artifact_stage},
+                                 {"runfiles", result.runfiles},
+                                 {"provides", result.provides}}}}
+            .ToJson(JsonMode::SerializeAllButNodes);
+    }
+    if (IsNode() and mode != JsonMode::NullForNonJson) {
+        switch (mode) {
+            case JsonMode::SerializeAll:
+                return Node().ToJson();
+            case JsonMode::SerializeAllButNodes:
+                return {{"type", "NODE"}, {"id", ToIdentifier()}};
+            default:
+                break;
+        }
+    }
+    if (IsList()) {
+        auto json = nlohmann::json::array();
+        auto const& list = List();
+        std::transform(list.begin(),
+                       list.end(),
+                       std::back_inserter(json),
+                       [mode](auto const& e) { return e->ToJson(mode); });
+        return json;
+    }
+    if (IsMap()) {
+        auto json = nlohmann::json::object();
+        auto const& map = Value<map_t>()->get();
+        std::for_each(map.begin(), map.end(), [&](auto const& p) {
+            json.emplace(p.first, p.second->ToJson(mode));
+        });
+        return json;
+    }
+    if (IsName() and mode != JsonMode::NullForNonJson) {
+        return Name().ToJson();
+    }
+    return nlohmann::json{};
+}
+
+auto Expression::IsCacheable() const -> bool {
+    // Must be updated whenever we add a new non-cacheable value
+    if (IsName()) {
+        return false;
+    }
+    if (IsResult()) {
+        return Result().is_cacheable;
+    }
+    if (IsNode()) {
+        return Node().IsCacheable();
+    }
+    if (IsList()) {
+        for (auto const& entry : List()) {
+            if (not entry->IsCacheable()) {
+                return false;
+            }
+        }
+    }
+    if (IsMap()) {
+        for (auto const& [key, entry] : Map()) {
+            if (not entry->IsCacheable()) {
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
+auto Expression::ToString() const -> std::string {
+    return ToJson().dump();
+}
+
+auto Expression::ToHash() const noexcept -> std::string {
+    if (hash_.load() == nullptr) {
+        if (not hash_loading_.exchange(true)) {
+            hash_ = std::make_shared<std::string>(ComputeHash());
+            hash_.notify_all();
+        }
+        else {
+            hash_.wait(nullptr);
+        }
+    }
+    return *hash_.load();
+}
+
+auto Expression::FromJson(nlohmann::json const& json) noexcept
+    -> ExpressionPtr {
+    if (json.is_null()) {
+        return ExpressionPtr{none_t{}};
+    }
+    try {  // try-catch because json.get<>() could throw, although checked
+        if (json.is_boolean()) {
+            return ExpressionPtr{json.get<bool>()};
+        }
+        if (json.is_number()) {
+            return ExpressionPtr{json.get<number_t>()};
+        }
+        if (json.is_string()) {
+            return ExpressionPtr{std::string{json.get<std::string>()}};
+        }
+        if (json.is_array()) {
+            auto l = Expression::list_t{};
+            l.reserve(json.size());
+            std::transform(json.begin(),
+                           json.end(),
+                           std::back_inserter(l),
+                           [](auto const& j) { return FromJson(j); });
+            return ExpressionPtr{l};
+        }
+        if (json.is_object()) {
+            auto m = Expression::map_t::underlying_map_t{};
+            for (auto& el : json.items()) {
+                m.emplace(el.key(), FromJson(el.value()));
+            }
+            return ExpressionPtr{Expression::map_t{m}};
+        }
+    } catch (...) {
+        gsl_EnsuresAudit(false);  // ensure that the try-block never throws
+    }
+    return ExpressionPtr{nullptr};
+}
+
+template <size_t kIndex>
+auto Expression::TypeStringForIndex() const noexcept -> std::string {
+    using var_t = decltype(data_);
+    if (kIndex == data_.index()) {
+        return TypeToString<std::variant_alternative_t<kIndex, var_t>>();
+    }
+    constexpr auto size = std::variant_size_v<var_t>;
+    if constexpr (kIndex < size - 1) {
+        return TypeStringForIndex<kIndex + 1>();
+    }
+    return TypeToString<std::variant_alternative_t<size - 1, var_t>>();
+}
+
+auto Expression::TypeString() const noexcept -> std::string {
+    return TypeStringForIndex();
+}
+
+auto Expression::ComputeHash() const noexcept -> std::string {
+    auto hash = std::string{};
+    if (IsNone() or IsBool() or IsNumber() or IsString() or IsArtifact() or
+        IsResult() or IsNode() or IsName()) {
+        // just hash the JSON representation, but prepend "@" for artifact,
+        // "=" for result, "#" for node, and "$" for name.
+        std::string prefix{
+            IsArtifact()
+                ? "@"
+                : IsResult() ? "=" : IsNode() ? "#" : IsName() ? "$" : ""};
+        hash = hash_gen_.Run(prefix + ToString()).Bytes();
+    }
+    else {
+        auto hasher = hash_gen_.IncrementalHasher();
+        if (IsList()) {
+            auto list = Value<Expression::list_t>();
+            hasher.Update("[");
+            for (auto const& el : list->get()) {
+                hasher.Update(el->ToHash());
+            }
+        }
+        else if (IsMap()) {
+            auto map = Value<Expression::map_t>();
+            hasher.Update("{");
+            for (auto const& el : map->get()) {
+                hasher.Update(hash_gen_.Run(el.first).Bytes());
+                hasher.Update(el.second->ToHash());
+            }
+        }
+        auto digest = std::move(hasher).Finalize();
+        if (not digest) {
+            Logger::Log(LogLevel::Error, "Failed to finalize hash.");
+            std::terminate();
+        }
+        hash = digest->Bytes();
+    }
+    return hash;
+}