Add physical partition detection fallback logic to AndroidBuild

Bug: b/472553631

Author: Databean

base/cvd/cuttlefish/host/commands/assemble_cvd/android_build/BUILD.bazel

@@ -129,6 +129,16 @@ cf_cc_library(
     ],
 )
 
+cf_cc_library(
+    name = "physical_partitions",
+    srcs = ["physical_partitions.cc"],
+    hdrs = ["physical_partitions.h"],
+    deps = [
+        "//cuttlefish/host/commands/assemble_cvd/android_build",
+        "//cuttlefish/result",
+    ],
+)
+
 cf_cc_library(
     name = "super_image",
     srcs = ["super_image.cc"],

base/cvd/cuttlefish/host/commands/assemble_cvd/android_build/physical_partitions.cc

@@ -0,0 +1,70 @@
+//
+// Copyright (C) 2025 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "cuttlefish/host/commands/assemble_cvd/android_build/physical_partitions.h"
+
+#include <functional>
+#include <memory>
+#include <ostream>
+#include <set>
+
+#include "cuttlefish/host/commands/assemble_cvd/android_build/android_build.h"
+#include "cuttlefish/result/result.h"
+
+namespace cuttlefish {
+namespace {
+
+class PhysicalPartitionsImpl : public AndroidBuild {
+ public:
+  PhysicalPartitionsImpl(AndroidBuild& build) : build_(build) {}
+
+  Result<std::set<std::string, std::less<void>>> PhysicalPartitions() override {
+    if (auto res = build_.PhysicalPartitions(); res.ok()) {
+      return *res;
+    }
+
+    std::set<std::string, std::less<void>> partitions =
+        CF_EXPECT(build_.Images());
+    for (std::string logical : CF_EXPECT(build_.LogicalPartitions())) {
+      partitions.erase(logical);
+    }
+
+    if (partitions.count("super_empty")) {
+      partitions.erase("super_empty");
+      partitions.insert("super");
+    }
+
+    return partitions;
+  }
+
+ private:
+  std::ostream& Format(std::ostream& out) const override {
+    return out << "PhysicalPartitions";
+  }
+
+  AndroidBuild& build_;
+};
+
+}  // namespace
+
+Result<std::unique_ptr<AndroidBuild>> PhysicalPartitions(AndroidBuild& build) {
+  auto partitions = std::make_unique<PhysicalPartitionsImpl>(build);
+
+  CF_EXPECT(partitions->PhysicalPartitions());
+
+  return partitions;
+}
+
+}  // namespace cuttlefish

base/cvd/cuttlefish/host/commands/assemble_cvd/android_build/physical_partitions.h

@@ -0,0 +1,37 @@
+//
+// Copyright (C) 2025 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <memory>
+
+#include "cuttlefish/host/commands/assemble_cvd/android_build/android_build.h"
+#include "cuttlefish/result/result.h"
+
+namespace cuttlefish {
+
+/**
+ * Wrap an `AndroidBuild` with fallback physical partition detection logic.
+ *
+ * If the `AndroidBuild` does not already provide GPT entry information, this
+ * makes a best guess based on known logical partitions and image files.
+ *
+ * One use case is the android product directory or `m` case, where the build
+ * system produces a collection of `.img` files including a `super.img`, but no
+ * explicit list of physical partitions.
+ */
+Result<std::unique_ptr<AndroidBuild>> PhysicalPartitions(AndroidBuild&);
+
+}  // namespace cuttlefish