ArtifactsRoot: support rehash-function

When constructing a git tree out of an artifact stage, support
rehashing the artifact digests on the fly, so that artifact stages
not based on GitSHA1 can be supported as well.

3 files changed, 24 insertions, 15 deletions

diff --git a/src/buildtool/computed_roots/TARGETS b/src/buildtool/computed_roots/TARGETS
index bb2bc0a4..e1d9bd79 100644
--- a/src/buildtool/computed_roots/TARGETS
+++ b/src/buildtool/computed_roots/TARGETS
@@ -29,7 +29,9 @@
   , "stage": ["src", "buildtool", "computed_roots"]
   , "deps":
     [ ["src/buildtool/build_engine/expression", "expression_ptr_interface"]
+    , ["src/buildtool/execution_api/utils", "rehash_utils"]
     , ["src/buildtool/multithreading", "async_map_consumer"]
+    , ["src/utils/cpp", "expected"]
     ]
   , "private-deps":
     [ ["@", "fmt", "", "fmt"]
diff --git a/src/buildtool/computed_roots/artifacts_root.cpp b/src/buildtool/computed_roots/artifacts_root.cpp
index 8124461b..1fa5ee7d 100644
--- a/src/buildtool/computed_roots/artifacts_root.cpp
+++ b/src/buildtool/computed_roots/artifacts_root.cpp
@@ -31,6 +31,7 @@
 #include "src/buildtool/common/artifact_digest.hpp"
 #include "src/buildtool/file_system/git_repo.hpp"
 #include "src/buildtool/file_system/object_type.hpp"
+#include "src/utils/cpp/expected.hpp"
 #include "src/utils/cpp/hex_string.hpp"
 
 namespace {
@@ -138,7 +139,8 @@ struct PartialTree {
 }  // namespace
 
 auto ArtifactsRoot(ExpressionPtr const& stage,
-                   AsyncMapConsumerLoggerPtr const& logger)
+                   AsyncMapConsumerLoggerPtr const& logger,
+                   std::optional<RehashUtils::Rehasher> const& rehash)
     -> std::optional<std::string> {
     if (not stage->IsMap()) {
         (*logger)(fmt::format("Expected stage to be a map, but found {}",
@@ -167,23 +169,26 @@ auto ArtifactsRoot(ExpressionPtr const& stage,
                       true);
             return std::nullopt;
         }
-        auto digest = val.ToArtifact().Digest();
-        if (not digest) {
-            (*logger)(
-                fmt::format("Failed to determine digest of known artifact {}",
-                            entry->ToString()),
-                true);
-            return std::nullopt;
-        }
-        auto ot = val.ToArtifact().Type();
-        if (not ot) {
-            (*logger)(fmt::format("Failed to determine object typle of known "
+        auto info_opt = val.ToArtifact().Info();
+        if (not info_opt) {
+            (*logger)(fmt::format("Failed to determine artifact info of known "
                                   "artifact {}",
                                   entry->ToString()),
                       true);
             return std::nullopt;
         }
-        if (not partial_tree.Add(ps, digest->hash(), *ot, logger)) {
+        auto info = *info_opt;
+        if (rehash) {
+            auto rehash_result = rehash->Rehash(info);
+            if (not rehash_result) {
+                (*logger)(
+                    fmt::format("Rehashing failed: {}", rehash_result.error()),
+                    true);
+                return std::nullopt;
+            }
+            info = *rehash_result;
+        }
+        if (not partial_tree.Add(ps, info.digest.hash(), info.type, logger)) {
             return std::nullopt;
         }
     }
diff --git a/src/buildtool/computed_roots/artifacts_root.hpp b/src/buildtool/computed_roots/artifacts_root.hpp
index 6ed727fa..95b72877 100644
--- a/src/buildtool/computed_roots/artifacts_root.hpp
+++ b/src/buildtool/computed_roots/artifacts_root.hpp
@@ -19,6 +19,7 @@
 #include <string>
 
 #include "src/buildtool/build_engine/expression/expression_ptr.hpp"
+#include "src/buildtool/execution_api/utils/rehash_utils.hpp"
 #include "src/buildtool/multithreading/async_map_consumer.hpp"
 
 /// \brief Compute to the git tree identifier, as hex string, corresponding to
@@ -28,7 +29,8 @@
 /// \param logger Logger to report problems; will be called with the fatal
 /// property in case of error
 auto ArtifactsRoot(ExpressionPtr const& stage,
-                   AsyncMapConsumerLoggerPtr const& logger)
-    -> std::optional<std::string>;
+                   AsyncMapConsumerLoggerPtr const& logger,
+                   std::optional<RehashUtils::Rehasher> const& rehash =
+                       std::nullopt) -> std::optional<std::string>;
 
 #endif