[Diff][Fixed] Assumption that all tags are in the trunk

- As stated by @matthijskooijman in
  91ffb04661c40102bfb856669039f0825ecc6883#r113724588 comment
  using --tags isn't necessary and includes *all* tags
- The code also assumed nothing was added before the "tag: "
  label, but this isn't true if the HEAD is tagged.

kibot/out_diff.py

@@ -254,21 +254,22 @@ class DiffOptions(BaseOptions):
     def process_tags(self, num):
         # Get a list of all tags ... and commits (how can I filter it?)
         logger.debug('Looking for git tags')
-        res = self.run_git(['rev-list', '--tags', '--format=format:%D'])
+        res = self.run_git(['rev-list', '--format=format:%D', 'HEAD'])
         if not res:
             return res
         res = res.split('\n')
         commit = ''
         skipped = 0
         for v in res:
-            if v.startswith('tag: '):
-                tag = v.split(',')[0][4:]
+            try:
+                tag = v[v.index('tag: '):].split(',')[0][4:]
                 logger.debugl(2, '- {}/{} tag: {} -> {}'.format(skipped, num, tag, commit))
                 if skipped == num:
                     return commit
                 skipped += 1
-            elif v.startswith('commit '):
-                commit = v[7:]
+            except ValueError:
+                if v.startswith('commit '):
+                    commit = v[7:]
 
     def solve_kibot_magic(self, name, tag):
         # The magic KIBOT_*

tests/test_plot/test_misc.py

@@ -1479,6 +1479,54 @@ def test_diff_git_4(test_dir):
     ctx.clean_up(keep_project=True)
 
 
+def test_diff_git_5(test_dir):
+    """ Difference between the two repo points, using tags """
+    prj = 'light_control'
+    yaml = 'diff_git_5'
+    ctx = context.TestContext(test_dir, prj, yaml)
+    # Create a git repo
+    git_init(ctx)
+    # Copy the "old" file
+    pcb = prj+'.kicad_pcb'
+    file = ctx.get_out_path(pcb)
+    shutil.copy2(ctx.board_file, file)
+    shutil.copy2(ctx.board_file.replace('.kicad_pcb', context.KICAD_SCH_EXT),
+                 file.replace('.kicad_pcb', context.KICAD_SCH_EXT))
+    # Add it to the repo
+    ctx.run_command(['git', 'add', pcb], chdir_out=True)
+    ctx.run_command(['git', 'commit', '-m', 'Reference'], chdir_out=True)
+    # Tag it (this will be our target)
+    ctx.run_command(['git', 'tag', '-a', 't1', '-m', 't1'], chdir_out=True)
+    # Add an extra commit
+    dummy = ctx.get_out_path('dummy')
+    with open(dummy, 'wt') as f:
+        f.write('dummy\n')
+    ctx.run_command(['git', 'add', 'dummy'], chdir_out=True)
+    ctx.run_command(['git', 'commit', '-m', 'Dummy noise'], chdir_out=True)
+    # Add a noisy branch
+    ctx.run_command(['git', 'switch', '-c', 'a_branch'], chdir_out=True)
+    # Copy the "new" file
+    with open(file, 'wt') as f:
+        f.write('broken\n')
+    # Add it to the repo
+    ctx.run_command(['git', 'commit', '-a', '-m', 'New version'], chdir_out=True)
+    # Tag it (this shouldn't be a problem)
+    ctx.run_command(['git', 'tag', '-a', 't2', '-m', 't2'], chdir_out=True)
+    # Back to the master
+    ctx.run_command(['git', 'checkout', 'master'], chdir_out=True)
+    # Copy the "new" file
+    shutil.copy2(ctx.board_file.replace(prj, prj+'_diff'), file)
+    # Add it to the repo
+    ctx.run_command(['git', 'add', pcb], chdir_out=True)
+    ctx.run_command(['git', 'commit', '-m', 'New version'], chdir_out=True)
+    # Tag it (this shouldn't be a problem)
+    ctx.run_command(['git', 'tag', '-a', 't3', '-m', 't3'], chdir_out=True)
+    # Run the test
+    ctx.run(extra=['-b', file], no_board_file=True, extra_debug=True)
+    ctx.compare_pdf(prj+'-diff_pcb.pdf', off_y=OFFSET_Y, tol=DIFF_TOL)
+    ctx.clean_up(keep_project=True)
+
+
 @pytest.mark.slow
 @pytest.mark.eeschema
 def test_diff_file_sch_1(test_dir):