TW-1583: Invalid ID displayed after done/delete

- Fix completed/deleted tasks getting an ID when GC is going to be run,
  previously resulting in invalid IDs being displayed in reports that
  show non-pending tasks.

A side effect of this fix is that it is sometimes not possible to
filter by ID when running a report right after calling done/delete.
This problem existed before; this change makes it happen on the first
report instead of the second, so it is more consistently broken.
Commands that modify tasks are not affected, making this an annoying
yet harmless defect.

ChangeLog

@@ -6,6 +6,8 @@
 - TW-1581 Tasks with dependencies show wrong urgency values for the first
   report run after a task in the dependency chain is completed/deleted (thanks
   to Ulf Eliasson).
+- TW-1583 Invalid ID displayed for first report after done/delete (thanks to
+  Ulf Eliasson).
 - Setting 'bulk' to zero is interpreted as infinity, which means there is no
   amount of changes that is considered dangerous (thanks to Tomas Babej).
 

src/Context.cpp

@@ -101,6 +101,7 @@ Context::Context ()
 , dom ()
 , determine_color_use (true)
 , use_color (true)
+, run_gc (true)
 , verbosity_legacy (false)
 , terminal_width (0)
 , terminal_height (0)
@@ -478,7 +479,14 @@ int Context::dispatch (std::string &out)
     // GC is invoked prior to running any command that displays task IDs, if
     // possible.
     if (c->displays_id () && !tdb2.read_only ())
+    {
+      run_gc = true;
       tdb2.gc ();
+    }
+    else
+    {
+      run_gc = false;
+    }
 
 /*
     // Only read-only commands can be run when TDB2 is read-only.

src/Context.h

@@ -94,6 +94,8 @@ public:
   bool                                determine_color_use;
   bool                                use_color;
 
+  bool                                run_gc;
+
   bool                                verbosity_legacy;
   std::vector <std::string>           verbosity;
   std::vector <std::string>           headers;

src/TDB2.cpp

@@ -316,9 +316,15 @@ void TF2::load_tasks ()
       ++line_number;
       Task task (*i);
 
-      // Some tasks gets an ID.
+      // Some tasks get an ID.
       if (_has_ids)
-        task.id = context.tdb2.next_id ();
+      {
+        Task::status status = task.getStatus ();
+        // Completed / deleted tasks in pending.data get an ID if GC is off.
+        if (!context.run_gc ||
+            (status != Task::completed && status != Task::deleted))
+          task.id = context.tdb2.next_id ();
+      }
 
       _tasks.push_back (task);
 

test/export.t

@@ -108,8 +108,10 @@ class TestExportCommand(TestCase):
     def test_export_end(self):
         self.t(('1', 'start'))
         self.t.faketime("+5s")
-        self.t(('1', 'done'))
-        self.assertTimestamp(self.export(1)['end'])
+        # After a task is "done" or "deleted", it does not have an ID by which
+        # to filter it anymore. Add a tag to work around this.
+        self.t(('1', 'done', '+workaround'))
+        self.assertTimestamp(self.export('+workaround')['end'])
 
     def test_export_due(self):
         self.t(('1', 'modify', 'due:today'))