QSysInfo: fall back to /usr/lib/os-release if the /etc one is missing

Turns out that there are two files and while a lot of distros symlink
one to the other, some distros lack the one in /etc.

[ChangeLog][QtCore][QSysInfo] Fixed QSysInfo::productType() to properly
detect some Linux distributions that ship with a minimal /etc.

Change-Id: Ia741b559c24d46c78fb2fffd1548cab414037220
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 13 insertions, 4 deletions

diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index a6990b88f4..b30d690025 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -2211,10 +2211,19 @@ static bool readEtcFile(QUnixOSVersion &v, const char *filename,
     return true;
 }
 
-static bool readEtcOsRelease(QUnixOSVersion &v)
+static bool readOsRelease(QUnixOSVersion &v)
 {
-    return readEtcFile(v, "/etc/os-release", QByteArrayLiteral("ID="),
-                       QByteArrayLiteral("VERSION_ID="), QByteArrayLiteral("PRETTY_NAME="));
+    QByteArray id = QByteArrayLiteral("ID=");
+    QByteArray versionId = QByteArrayLiteral("VERSION_ID=");
+    QByteArray prettyName = QByteArrayLiteral("PRETTY_NAME=");
+
+    // man os-release(5) says:
+    // The file /etc/os-release takes precedence over /usr/lib/os-release.
+    // Applications should check for the former, and exclusively use its data
+    // if it exists, and only fall back to /usr/lib/os-release if it is
+    // missing.
+    return readEtcFile(v, "/etc/os-release", id, versionId, prettyName) ||
+            readEtcFile(v, "/usr/lib/os-release", id, versionId, prettyName);
 }
 
 static bool readEtcLsbRelease(QUnixOSVersion &v)
@@ -2296,7 +2305,7 @@ static bool readEtcDebianVersion(QUnixOSVersion &v)
 
 static bool findUnixOsVersion(QUnixOSVersion &v)
 {
-    if (readEtcOsRelease(v))
+    if (readOsRelease(v))
         return true;
     if (readEtcLsbRelease(v))
         return true;