From cdff63405771982166e5ce0f9f343d8b8b1a92d5 Mon Sep 17 00:00:00 2001
From: Weaselbot <weaselbot@weaselab.dev>
Date: Sun, 19 Jul 2026 22:00:15 -0400
Subject: [PATCH] Fix schemagen integer parser rejecting zero with negative
 exponents

Move the zero-detection check in the generated parseJsonInt64 before the
finalExp < 0 guard. Previously, valid JSON numbers whose mathematical
value is 0 but written with a large negative exponent (e.g. 0e-2,
0.0e-2, -0e-2, 0e-20) were rejected because the negative-finalExp early
return ran before the all-zero-digits branch could set out = 0. Non-zero
values with negative exponents are still correctly rejected.

Closes #56
---
 contrib/schemagen/test_schemagen.py       | 10 ++++++++++
 contrib/schemagen/weaseljson_schemagen.py |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/contrib/schemagen/test_schemagen.py b/contrib/schemagen/test_schemagen.py
index a3e4425..4b4eed9 100644
--- a/contrib/schemagen/test_schemagen.py
+++ b/contrib/schemagen/test_schemagen.py
@@ -592,6 +592,13 @@ class SchemagenIntegerBoundaryTest(unittest.TestCase):
             ("123.0", "WeaselJson_OK", 123),
             ("9e18", "WeaselJson_OK", 9000000000000000000),
             ("10e18", "WeaselJson_REJECT", 0),
+            # Issue #56: zero written with a negative exponent must be accepted.
+            ("0e-1", "WeaselJson_OK", 0),
+            ("0e-2", "WeaselJson_OK", 0),
+            ("0.0e-2", "WeaselJson_OK", 0),
+            ("-0e-2", "WeaselJson_OK", 0),
+            ("0e-20", "WeaselJson_OK", 0),
+            ("0.000e-5", "WeaselJson_OK", 0),
         ]
         cases_src = self._build_cases_array("root", cases)
         harness = textwrap.dedent(
@@ -634,6 +641,9 @@ class SchemagenIntegerBoundaryTest(unittest.TestCase):
             ('{"age":2.0}', "WeaselJson_OK", 2),
             ('{"age":0.0001e4}', "WeaselJson_OK", 1),
             ('{"age":0.001}', "WeaselJson_REJECT", 0),
+            # Issue #56: zero written with a negative exponent must be accepted.
+            ('{"age":0e-2}', "WeaselJson_OK", 0),
+            ('{"age":-0e-20}', "WeaselJson_OK", 0),
             (
                 '{"age":-9223372036854775808.0}',
                 "WeaselJson_OK",
diff --git a/contrib/schemagen/weaseljson_schemagen.py b/contrib/schemagen/weaseljson_schemagen.py
index 2283454..32ae08e 100644
--- a/contrib/schemagen/weaseljson_schemagen.py
+++ b/contrib/schemagen/weaseljson_schemagen.py
@@ -1058,10 +1058,10 @@ private:
       ++trim;
     }}
     int64_t finalExp = exp - fracDigits + trim;
-    if (finalExp < 0) return false;
     size_t leadingZeros = 0;
     while (leadingZeros < digits.size() && digits[leadingZeros] == '0') ++leadingZeros;
     if (leadingZeros == digits.size()) {{ out = 0; return true; }}
+    if (finalExp < 0) return false;
     if (leadingZeros > 0) digits.erase(0, leadingZeros);
 
     constexpr uint64_t kMaxNeg = 9223372036854775808ULL;