files: add force flag

Enabling this flag for a `home.file` entry causes the target to be
unconditionally overwritten. The option is not visible in
documentation for now and shouldn't be relied on for general use.

(cherry picked from commit 37694e9f51)

modules/files.nix

@@ -45,6 +45,13 @@ in
     # overwrite an existing file.
     home.activation.checkLinkTargets = dag.entryBefore ["writeBoundary"] (
       let
+        # Paths that should be forcibly overwritten by Home Manager.
+        # Caveat emptor!
+        forcedPaths =
+          concatMapStringsSep " " (p: ''"$HOME/${p}"'')
+            (mapAttrsToList (n: v: v.target)
+            (filterAttrs (n: v: v.force) cfg));
+
         check = pkgs.writeText "check" ''
           . ${./lib-bash/color-echo.sh}
 
@@ -52,12 +59,25 @@ in
           # considered part of a Home Manager generation.
           homeFilePattern="$(readlink -e "${builtins.storeDir}")/*-home-manager-files/*"
 
+          forcedPaths=(${forcedPaths})
+
           newGenFiles="$1"
           shift
           for sourcePath in "$@" ; do
             relativePath="''${sourcePath#$newGenFiles/}"
             targetPath="$HOME/$relativePath"
-            if [[ -e "$targetPath" \
+
+            forced=""
+            for forcedPath in "''${forcedPaths[@]}"; do
+              if [[ $targetPath == $forcedPath* ]]; then
+                forced="yeah"
+                break
+              fi
+            done
+
+            if [[ -n $forced ]]; then
+              $VERBOSE_ECHO "Skipping collision check for $targetPath"
+            elif [[ -e "$targetPath" \
                 && ! "$(readlink "$targetPath")" == $homeFilePattern ]] ; then
               if [[ ! -L "$targetPath" && -n "$HOME_MANAGER_BACKUP_EXT" ]] ; then
                 backup="$targetPath.$HOME_MANAGER_BACKUP_EXT"

modules/lib/file-type.nix

@@ -86,6 +86,18 @@ in
             into place.
           '';
         };
+
+        force = mkOption {
+          type = types.bool;
+          default = false;
+          visible = false;
+          description = ''
+            Whether the target path should be unconditionally replaced
+            by the managed file source. Warning, this will silently
+            delete the target regardless of whether it is a file or
+            link.
+          '';
+        };
       };
 
       config = {