[preservefiles] Use ${} expansion instead of @@

SEE #1438

CHANGES-3.3

@@ -61,4 +61,5 @@ Pre-release versions:
  - *partition* requires KPMCore 21.12 (e.g. KPMCore 4.2 API, or later).
  - *partition* can now skip installing the bootloader in more scenarios.
    #1632 (Thanks Anubhav)
+ - *preservefiles* follows `${}` variable syntax instead of `@@`.
 

src/modules/preservefiles/PreserveFiles.cpp

@@ -15,6 +15,7 @@
 #include "utils/CalamaresUtilsSystem.h"
 #include "utils/CommandList.h"
 #include "utils/Logger.h"
+#include "utils/StringExpander.h"
 #include "utils/Units.h"
 
 #include <QFile>
@@ -37,7 +38,8 @@ atReplacements( QString s )
         user = gs->value( "username" ).toString();
     }
 
-    return s.replace( "@@ROOT@@", root ).replace( "@@USER@@", user );
+    Calamares::String::DictionaryExpander d;
+    return d.add( QStringLiteral( "ROOT" ), root ).add( QStringLiteral( "USER" ), user ).expand( s );
 }
 
 PreserveFiles::PreserveFiles( QObject* parent )

src/modules/preservefiles/preservefiles.conf

@@ -40,11 +40,11 @@
 #     not exist in the host system (e.g. nvidia configuration files that
 #     are created in some boot scenarios and not in others).
 #
-# The target path (*dest*) is modified as follows:
+# The target path (*dest*) is modified by expanding variables in `${}`:
-#   - `@@ROOT@@` is replaced by the path to the target root (may be /).
+#   - `ROOT` is replaced by the path to the target root (may be /).
 #     There is never any reason to use this, since the *dest* is already
 #     interpreted in the target system.
-#   - `@@USER@@` is replaced by the username entered by on the user
+#   - `USER` is replaced by the username entered by on the user
 #       page (may be empty, for instance if no user page is enabled)
 #
 #
@@ -53,6 +53,9 @@ files:
   - from: log
     dest: /var/log/Calamares.log
     perm: root:wheel:600
+  - from: log
+    dest: /home/${USER}/installation.log
+    optional: true
   - from: config
     dest: /var/log/Calamares-install.json
     perm: root:wheel:600