Fix %g formatting of floats < 0.0

Author: steve-s

graalpython/com.oracle.graal.python.test/src/tests/test_formatting.py

@@ -114,6 +114,7 @@ def test_complex_formatting():
     assert format(complex(1, float("Inf")), "") == "(1+infj)"
     assert format(MyComplex(3j), "") == "42"
     assert format(MyComplex(3j), " <5") == "3j   "
+    assert format(complex(2**53 + 1, 0)) == '(9007199254740992+0j)'
 
 
 class AnyRepr:

graalpython/com.oracle.graal.python.test/src/tests/unittest_tags/test_complex.txt

@@ -3,6 +3,7 @@
 *graalpython.lib-python.3.test.test_complex.ComplexTest.test_conjugate
 *graalpython.lib-python.3.test.test_complex.ComplexTest.test_divmod
 *graalpython.lib-python.3.test.test_complex.ComplexTest.test_file
+*graalpython.lib-python.3.test.test_complex.ComplexTest.test_format
 *graalpython.lib-python.3.test.test_complex.ComplexTest.test_getnewargs
 *graalpython.lib-python.3.test.test_complex.ComplexTest.test_neg
 *graalpython.lib-python.3.test.test_complex.ComplexTest.test_negated_imaginary_literal

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/formatting/FloatFormatter.java

@@ -55,6 +55,7 @@ public FloatFormatter(PythonCore core, FormattingBuffer result, Spec spec, boole
             minFracDigits = 0;
         } else if (spec.alternate) {
             // Alternate form means do not trim the zero fractional digits.
+            // This should be equivalent to Py_DTSF_ALT flag in CPython
             minFracDigits = -1;
         } else if (spec.type == 'r' || spec.type == Spec.NONE) {
             // These formats by default show at least one fractional digit.
@@ -649,11 +650,10 @@ private void appendFixed(CharSequence digits, int exp, int precision) {
                 }
                 lenWhole = digitCount;
             }
-
-            if (noTruncate) {
-                // Extend the fraction as BigDecimal will have economised on zeros.
-                appendPointAndTrailingZeros(precision - digitCount);
-            }
+        }
+        if (noTruncate) {
+            // Extend the fraction as BigDecimal will have economised on zeros.
+            appendPointAndTrailingZeros(lenFraction + precision - digitCount);
         }
 
         // Finally, ensure we have all and only the fractional digits we should.