Bug 1894412 - When reading /etc/os-release, fall back to BUILD_ID when...

Bug 1894412 - When reading /etc/os-release, fall back to BUILD_ID when VERSION_ID is not set.  a=dmeehan

Arch Linux doesn't come with a VERSION_ID at all, but it has a BUILD_ID.
Semantically, falling back to BUILD_ID when VERSION_ID is not present
would seem fair play:

Per https://www.freedesktop.org/software/systemd/man/latest/os-release.html:

BUILD_ID=
    A string uniquely identifying the system image originally used as the
    installation base. In most cases, VERSION_ID or IMAGE_ID+IMAGE_VERSION
    are updated when the entire system image is replaced during an update.
    BUILD_ID may be used in distributions where the original installation
    image version is important: VERSION_ID would change during incremental
    system updates, but BUILD_ID would not. This field is optional.

Original Revision: https://phabricator.services.mozilla.com/D209089

Differential Revision: https://phabricator.services.mozilla.com/D209192

widget/LSBUtils.cpp

@@ -45,6 +45,7 @@ bool GetOSRelease(nsACString& aDistributor, nsACString& aDescription,
   bool seen_id = false, seen_pretty_name = false, seen_version_id = false;
   std::string rawline;
   nsAutoCString name;
+  nsAutoCString build_id;
   while (std::getline(stream, rawline)) {
     std::string_view line(rawline);
     size_t pos = line.find('=');
@@ -68,6 +69,8 @@ bool GetOSRelease(nsACString& aDistributor, nsACString& aDescription,
         if (ExtractAndSetValue(aDescription, value)) seen_pretty_name = true;
       } else if (key == "VERSION_ID") {
         if (ExtractAndSetValue(aRelease, value)) seen_version_id = true;
+      } else if (key == "BUILD_ID") {
+        ExtractAndSetValue(build_id, value);
       } else if (key == "VERSION_CODENAME") {
         ExtractAndSetValue(aCodename, value);
       }
@@ -77,6 +80,11 @@ bool GetOSRelease(nsACString& aDistributor, nsACString& aDescription,
   if (seen_id && !name.IsEmpty() && name.EqualsIgnoreCase(aDistributor)) {
     aDistributor = name;
   }
+  // If VERSION_ID is not set but BUILD_ID is, use BUILD_ID.
+  if (!seen_version_id && !build_id.IsEmpty()) {
+    aRelease = build_id;
+    seen_version_id = true;
+  }
   // Only consider our work done if we've seen at least ID, PRETTY_NAME and
   // VERSION_ID.
   return seen_id && seen_pretty_name && seen_version_id;