--dl-trades should also support increasing download span

(by downloading the whole dataset again to avoid missing data in the
middle).

freqtrade/data/history/history_utils.py

@@ -270,6 +270,11 @@ def _download_trades_history(exchange: Exchange,
         # DEFAULT_TRADES_COLUMNS: 0 -> timestamp
         # DEFAULT_TRADES_COLUMNS: 1 -> id
 
+        if trades and since < trades[0][0]:
+            # since is before the first trade
+            logger.info(f"Start earlier than available data. Redownloading trades for {pair}...")
+            trades = []
+
         from_id = trades[-1][1] if trades else None
         if trades and since < trades[-1][0]:
             # Reset since to the last available point

tests/conftest.py

@@ -1424,7 +1424,7 @@ def trades_for_order():
 
 @pytest.fixture(scope="function")
 def trades_history():
-    return [[1565798399463, '126181329', None, 'buy', 0.019627, 0.04, 0.00078508],
+    return [[1565798389463, '126181329', None, 'buy', 0.019627, 0.04, 0.00078508],
             [1565798399629, '126181330', None, 'buy', 0.019627, 0.244, 0.004788987999999999],
             [1565798399752, '126181331', None, 'sell', 0.019626, 0.011, 0.00021588599999999999],
             [1565798399862, '126181332', None, 'sell', 0.019626, 0.011, 0.00021588599999999999],

tests/data/test_history.py

@@ -557,6 +557,7 @@ def test_download_trades_history(trades_history, mocker, default_conf, testdatad
     assert ght_mock.call_count == 1
     # Check this in seconds - since we had to convert to seconds above too.
     assert int(ght_mock.call_args_list[0][1]['since'] // 1000) == since_time2 - 5
+    assert ght_mock.call_args_list[0][1]['from_id'] is not None
 
     # clean files freshly downloaded
     _clean_test_file(file1)
@@ -568,6 +569,27 @@ def test_download_trades_history(trades_history, mocker, default_conf, testdatad
                                         pair='ETH/BTC')
     assert log_has_re('Failed to download historic trades for pair: "ETH/BTC".*', caplog)
 
+    file2 = testdatadir / 'XRP_ETH-trades.json.gz'
+
+    _backup_file(file2, True)
+
+    ght_mock.reset_mock()
+    mocker.patch('freqtrade.exchange.Exchange.get_historic_trades',
+                 ght_mock)
+    # Since before first start date
+    since_time = int(trades_history[0][0] // 1000) - 500
+    timerange = TimeRange('date', None, since_time, 0)
+
+    assert _download_trades_history(data_handler=data_handler, exchange=exchange,
+                                    pair='XRP/ETH', timerange=timerange)
+
+    assert ght_mock.call_count == 1
+
+    assert int(ght_mock.call_args_list[0][1]['since'] // 1000) == since_time
+    assert ght_mock.call_args_list[0][1]['from_id'] is None
+    assert log_has_re(r'Start earlier than available data. Redownloading trades for.*', caplog)
+    _clean_test_file(file2)
+
 
 def test_convert_trades_to_ohlcv(mocker, default_conf, testdatadir, caplog):