Make 'focus' disable blocking fullscreen windows

The problem here is that con_fullscreen_permits_focusing() does not
check if there is a blocking fullscreen container in the workspace that
the container to be focused belongs. This makes it possible to focus a
container behind a fullscreen window if it's in an unfocused workspace.

This commit introduces a change in the 'focus' command behaviour. When
focusing a container blocked by a fullscreen container, either CF_OUTPUT
or CF_GLOBAL, the blocking container loses its fullscreen mode and the
target container is focused like normal.

This should not affect directional focus commands: left, right, up,
down, parent, child.

Fixes issue #1819.

testcases/t/156-fullscreen-focus.t

@@ -157,9 +157,6 @@ isnt($x->input_focus, $right2->id, 'bottom right window no longer focused');
 cmd 'focus child';
 is($x->input_focus, $right2->id, 'bottom right window focused again');
 
-cmd '[id="' . $left->id . '"] focus';
-is($x->input_focus, $right2->id, 'prevented focus change to left window');
-
 cmd 'focus up';
 is($x->input_focus, $right1->id, 'allowed focus up');
 
@@ -178,9 +175,6 @@ is($x->input_focus, $right1->id, 'allowed focus wrap (down)');
 cmd 'focus up';
 is($x->input_focus, $right2->id, 'allowed focus wrap (up)');
 
-cmd '[id="' . $diff_ws->id . '"] focus';
-is($x->input_focus, $right2->id, 'prevented focus change to different ws');
-
 ################################################################################
 # Same tests when we're in non-global fullscreen mode. It should now be possible
 # to focus a container in a different workspace.
@@ -202,9 +196,6 @@ isnt($x->input_focus, $right2->id, 'bottom right window no longer focused');
 cmd 'focus child';
 is($x->input_focus, $right2->id, 'bottom right window focused again');
 
-cmd '[id="' . $left->id . '"] focus';
-is($x->input_focus, $right2->id, 'prevented focus change to left window');
-
 cmd 'focus up';
 is($x->input_focus, $right1->id, 'allowed focus up');
 
@@ -323,6 +314,105 @@ verify_move(2, 'prevented move to workspace by name');
 cmd "move to workspace prev";
 verify_move(2, 'prevented move to workspace by position');
 
-# TODO: Tests for "move to output" and "move workspace to output".
+################################################################################
+# Ensure it's possible to focus a window using the focus command despite
+# fullscreen window blocking it. Fullscreen window should lose its fullscreen
+# mode.
+################################################################################
 
+# first & second tiling, focus using id
+kill_all_windows;
+
+$tmp = fresh_workspace;
+my $first = open_window;
+my $second = open_window;
+cmd 'fullscreen';
+is($x->input_focus, $second->id, 'fullscreen window focused');
+is_num_fullscreen($tmp, 1, '1 fullscreen window');
+
+cmd '[id="'. $first->id .'"] focus';
+sync_with_i3;
+
+is($x->input_focus, $first->id, 'correctly focused using id');
+is_num_fullscreen($tmp, 0, 'no fullscreen windows');
+
+# first floating, second tiling, focus using 'focus floating'
+kill_all_windows;
+
+$tmp = fresh_workspace;
+my $first = open_floating_window;
+my $second = open_window;
+cmd 'fullscreen';
+is($x->input_focus, $second->id, 'fullscreen window focused');
+is_num_fullscreen($tmp, 1, '1 fullscreen window');
+
+cmd 'focus floating';
+sync_with_i3;
+
+is($x->input_focus, $first->id, 'correctly focused using focus floating');
+is_num_fullscreen($tmp, 0, 'no fullscreen windows');
+
+# first tiling, second floating, focus using 'focus tiling'
+kill_all_windows;
+
+$tmp = fresh_workspace;
+my $first = open_window;
+my $second = open_floating_window;
+cmd 'fullscreen';
+is($x->input_focus, $second->id, 'fullscreen window focused');
+is_num_fullscreen($tmp, 1, '1 fullscreen window');
+
+cmd 'focus tiling';
+sync_with_i3;
+
+is($x->input_focus, $first->id, 'correctly focused using focus tiling');
+is_num_fullscreen($tmp, 0, 'no fullscreen windows');
+
+################################################################################
+# When the fullscreen window is in an other workspace it should maintain its
+# fullscreen mode since it's not blocking the window to be focused.
+################################################################################
+
+kill_all_windows;
+
+$tmp = fresh_workspace;
+my $first = open_window;
+
+$tmp2 = fresh_workspace;
+my $second = open_window;
+cmd 'fullscreen';
+is($x->input_focus, $second->id, 'fullscreen window focused');
+is_num_fullscreen($tmp2, 1, '1 fullscreen window');
+
+cmd '[id="'. $first->id .'"] focus';
+sync_with_i3;
+
+is($x->input_focus, $first->id, 'correctly focused using focus id');
+is_num_fullscreen($tmp, 0, 'no fullscreen windows on first workspace');
+is_num_fullscreen($tmp2, 1, 'still one fullscreen window on second workspace');
+
+################################################################################
+# But a global window in another workspace is blocking the window to be focused.
+# Ensure that it loses its fullscreen mode.
+################################################################################
+
+kill_all_windows;
+
+$tmp = fresh_workspace;
+$first = open_window;
+
+$tmp2 = fresh_workspace;
+$second = open_window;
+cmd 'fullscreen global';
+is($x->input_focus, $second->id, 'global window focused');
+is_num_fullscreen($tmp2, 1, '1 fullscreen window');
+
+cmd '[id="'. $first->id .'"] focus';
+sync_with_i3;
+
+is($x->input_focus, $first->id, 'correctly focused using focus id');
+is_num_fullscreen($tmp2, 0, 'no fullscreen windows');
+
+
+# TODO: Tests for "move to output" and "move workspace to output".
 done_testing;