[partition] Address default-labeling issues

CHANGES-3.2

@@ -23,7 +23,7 @@ This release contains contributions from (alphabetically by name):
 ## Modules ##
  - *fstab* module correctly handles empty UUID strings. (Thanks Evan)
  - *partition* module no longer forgets configured partition-layouts.
-   (Thanks Santosh)
+   It also respects configured partition labels better. (Thanks Santosh)
 
 
 # 3.2.53 (2022-03-04) #

src/modules/partition/core/PartitionCoreModule.cpp

@@ -941,6 +941,15 @@ PartitionCoreModule::setBootLoaderInstallPath( const QString& path )
     m_bootLoaderInstallPath = path;
 }
 
+static void
+applyDefaultLabel( Partition* p, bool ( *predicate )( const Partition* ), const QString& label )
+{
+    if ( p->label().isEmpty() && predicate( p ) )
+    {
+        p->setLabel( label );
+    }
+}
+
 void
 PartitionCoreModule::layoutApply( Device* dev,
                                   qint64 firstSector,
@@ -957,25 +966,28 @@ PartitionCoreModule::layoutApply( Device* dev,
     // PartitionInfo::mountPoint() says where it will be mounted in the target system.
     // .. the latter is more interesting.
     //
-    // If we have a separate /boot, mark that one as bootable, otherwise mark
+    // If we have a separate /boot, mark that one as bootable,
-    // the root / as bootable.
+    // otherwise mark the root / as bootable.
     //
-    // TODO: perhaps the partition that holds the bootloader?
+    // If the layout hasn't applied a label to the partition,
+    //      apply a default label (to boot and root, at least).
+    const auto is_boot = []( const Partition* p ) -> bool
+    {
         const QString boot = QStringLiteral( "/boot" );
+        return PartitionInfo::mountPoint( p ) == boot || p->mountPoint() == boot;
+    };
+    const auto is_root = []( const Partition* p ) -> bool
+    {
         const QString root = QStringLiteral( "/" );
-    const auto is_boot
+        return PartitionInfo::mountPoint( p ) == root || p->mountPoint() == root;
-        = [ & ]( Partition* p ) -> bool { return PartitionInfo::mountPoint( p ) == boot || p->mountPoint() == boot; };
+    };
-    const auto is_root
-        = [ & ]( Partition* p ) -> bool { return PartitionInfo::mountPoint( p ) == root || p->mountPoint() == root; };
 
     const bool separate_boot_partition
         = std::find_if( partList.constBegin(), partList.constEnd(), is_boot ) != partList.constEnd();
     for ( Partition* part : partList )
     {
-        if ( is_boot( part ) )
+        applyDefaultLabel( part, is_root, QStringLiteral( "root" ) );
-        {
+        applyDefaultLabel( part, is_boot, QStringLiteral( "boot" ) );
-            part->setLabel( "boot" );
-        }
         if ( ( separate_boot_partition && is_boot( part ) ) || ( !separate_boot_partition && is_root( part ) ) )
         {
             createPartition(