fix LaTeX siunitx exponent formatting (closes #1515)

With siunitx, you can format a quantity in scientfic notation by
specifying the quantity's magnitude in 'e' notation.

\SI{1e2}{\meter}

Here, the '1e2' will expand to '1 \times 10^{2}'.

So, when Pint formats exponents for LaTeX, it should *not* expand '1e2'
to '1 \times 10^{2}' *if* siunitx is used.

This commit adds a check to disable expaning exponents for quantity
magnitude formatting if siunitx is used.

1 files changed, 2 insertions, 0 deletions

diff --git a/pint/testsuite/test_quantity.py b/pint/testsuite/test_quantity.py
index 196d0c3..7648d28 100644
--- a/pint/testsuite/test_quantity.py
+++ b/pint/testsuite/test_quantity.py
@@ -294,11 +294,13 @@ class TestQuantity(QuantityTestCase):
         x = ureg.Quantity(1e20, "meter")
         assert f"{x:~H}" == r"1×10<sup>20</sup> m"
         assert f"{x:~L}" == r"1\times 10^{20}\ \mathrm{m}"
+        assert f"{x:~Lx}" == r"\SI[]{1e+20}{\meter}"
         assert f"{x:~P}" == r"1×10²⁰ m"
 
         x /= 1e40
         assert f"{x:~H}" == r"1×10<sup>-20</sup> m"
         assert f"{x:~L}" == r"1\times 10^{-20}\ \mathrm{m}"
+        assert f"{x:~Lx}" == r"\SI[]{1e-20}{\meter}"
         assert f"{x:~P}" == r"1×10⁻²⁰ m"
 
     def test_ipython(self):