FileSource cleanups

- Add documentation
- Use `std::string_view` rather than `std::string`
- Expose formatting operations with abseil, libfmt, and ostream

Bug: b/464085167

Author: Databean

base/cvd/cuttlefish/host/libs/config/BUILD.bazel

@@ -219,6 +219,11 @@ cf_cc_library(
     name = "file_source",
     srcs = ["file_source.cc"],
     hdrs = ["file_source.h"],
+    deps = [
+        "@abseil-cpp//absl/strings",
+        "@abseil-cpp//absl/strings:str_format",
+        "@fmt",
+    ],
 )
 
 cf_cc_library(

base/cvd/cuttlefish/host/libs/config/fetcher_config.cpp

@@ -165,7 +165,7 @@ CvdFile JsonToCvdFile(const std::string& file_path, const Json::Value& json) {
 
 Json::Value CvdFileToJson(const CvdFile& cvd_file) {
   Json::Value json;
-  json[kCvdFileSource] = SourceEnumToString(cvd_file.source);
+  json[kCvdFileSource] = std::string(SourceEnumToString(cvd_file.source));
   json[kCvdFileBuildId] = cvd_file.build_id;
   json[kCvdFileBuildTarget] = cvd_file.build_target;
   json[kCvdFileArchiveSource] = cvd_file.archive_source;

base/cvd/cuttlefish/host/libs/config/file_source.cc

@@ -16,41 +16,40 @@
 
 #include "cuttlefish/host/libs/config/file_source.h"
 
-#include <cctype>
-#include <string>
+#include <ostream>
+#include <string_view>
+
+#include "absl/strings/match.h"
 
 namespace cuttlefish {
 
-FileSource SourceStringToEnum(std::string source) {
-  for (auto& c : source) {
-    c = std::tolower(c);
-  }
-  if (source == "default_build") {
+FileSource SourceStringToEnum(std::string_view source) {
+  if (absl::EqualsIgnoreCase(source, "default_build")) {
     return FileSource::DEFAULT_BUILD;
-  } else if (source == "system_build") {
+  } else if (absl::EqualsIgnoreCase(source, "system_build")) {
     return FileSource::SYSTEM_BUILD;
-  } else if (source == "kernel_build") {
+  } else if (absl::EqualsIgnoreCase(source, "kernel_build")) {
     return FileSource::KERNEL_BUILD;
-  } else if (source == "local_file") {
+  } else if (absl::EqualsIgnoreCase(source, "local_file")) {
     return FileSource::LOCAL_FILE;
-  } else if (source == "generated") {
+  } else if (absl::EqualsIgnoreCase(source, "generated")) {
     return FileSource::GENERATED;
-  } else if (source == "bootloader_build") {
+  } else if (absl::EqualsIgnoreCase(source, "bootloader_build")) {
     return FileSource::BOOTLOADER_BUILD;
-  } else if (source == "android_efi_loader_build") {
+  } else if (absl::EqualsIgnoreCase(source, "android_efi_loader_build")) {
     return FileSource::ANDROID_EFI_LOADER_BUILD;
-  } else if (source == "boot_build") {
+  } else if (absl::EqualsIgnoreCase(source, "boot_build")) {
     return FileSource::BOOT_BUILD;
-  } else if (source == "host_package_build") {
+  } else if (absl::EqualsIgnoreCase(source, "host_package_build")) {
     return FileSource::HOST_PACKAGE_BUILD;
-  } else if (source == "chrome_os_build") {
+  } else if (absl::EqualsIgnoreCase(source, "chrome_os_build")) {
     return FileSource::CHROME_OS_BUILD;
   } else {
     return FileSource::UNKNOWN_PURPOSE;
   }
 }
 
-std::string SourceEnumToString(const FileSource& source) {
+std::string_view SourceEnumToString(FileSource source) {
   if (source == FileSource::DEFAULT_BUILD) {
     return "default_build";
   } else if (source == FileSource::SYSTEM_BUILD) {
@@ -76,4 +75,8 @@ std::string SourceEnumToString(const FileSource& source) {
   }
 }
 
+std::ostream& operator<<(std::ostream& out, FileSource source) {
+  return out << SourceEnumToString(source);
+}
+
 }  // namespace cuttlefish

base/cvd/cuttlefish/host/libs/config/file_source.h

@@ -15,11 +15,22 @@
  */
 #pragma once
 
-#include <string>
+#include <ostream>
+#include <string_view>
+
+#include "absl/strings/str_format.h"
+#include "fmt/ostream.h"
 
 namespace cuttlefish {
 
-// Order in enum is not guaranteed to be stable, serialized as a string.
+/**
+ * When a file is downloaded from `cvd fetch`, this is the "reason" the file is
+ * downloaded. More specifically, whether it corresponds to the
+ * `--default_build` argument, the `--system_build` argument, `--kernel_build`,
+ * et cetera.
+ *
+ * Order in enum is not guaranteed to be stable, serialized as a string.
+ */
 enum class FileSource {
   UNKNOWN_PURPOSE = 0,
   DEFAULT_BUILD,
@@ -34,7 +45,21 @@ enum class FileSource {
   CHROME_OS_BUILD,
 };
 
-FileSource SourceStringToEnum(std::string source);
-std::string SourceEnumToString(const FileSource& source);
+FileSource SourceStringToEnum(std::string_view source);
+std::string_view SourceEnumToString(FileSource source);
+
+std::ostream& operator<<(std::ostream&, FileSource);
+
+template <typename Sink>
+void AbslStringify(Sink& sink, FileSource file_source) {
+  sink.Append(SourceEnumToString(file_source));
+}
 
 }  // namespace cuttlefish
+
+namespace fmt {
+
+template <>
+struct formatter<::cuttlefish::FileSource> : ostream_formatter {};
+
+}  // namespace fmt