`'%g' % 0` causes Overflow

[mark-rushakoff]

I have been chasing down a bug in my code that I thought had to do with a recursive object, but now I have reduced the problem to %g formatting being unable to render a 0.

I have checked out go-jsonnet at commit 51daeb3 (current master).

$ go version
go version go1.16.5 darwin/amd64

$ echo '"%f" % 0' | go run ./cmd/jsonnet - # %f works correctly
"0.000000"

$ echo '"%g" % 0' | go run ./cmd/jsonnet -
RUNTIME ERROR: Overflow
	<std>:648:38-59	thunk from <thunk <exponent> from <function <format_code>>>
	<std>:648:28-74	thunk <exponent> from <function <format_code>>
	<std>:649:14-22	function <format_code>
	<std>:722:15-60	thunk <s> from <function <format_codes_arr>>
	<std>:727:24-25	thunk from <thunk <s_padded> from <function <format_codes_arr>>>
	<std>:480:30-33	thunk from <thunk from <function <pad_left>>>
	<std>:480:19-34	thunk from <function <pad_left>>
	<std>:476:11-12	thunk from <function <padding>>
	<std>:472:12-13	function <aux>
	<std>:476:7-17	function <padding>
	<std>:480:7-38	function <pad_left>
	<std>:727:15-39	thunk <s_padded> from <function <format_codes_arr>>
	<std>:733:55-63	thunk from <function <format_codes_arr>>
	<std>:733:11-64	function <format_codes_arr>
	<std>:781:7-48	function <anonymous>
	<std>:237:7-23	function <anonymous>
	<stdin>:1:1-9
	During evaluation

exit status 1

I have confirmed that this behavior is present at least as far back as v0.13.0 of go-jsonnet, but I didn't check any older revisions.

[mark-rushakoff]

To clarify the expected output of '%g' % 0 is the string 0:

$ python -c "print(['%f' % 0, '%g' % 0])"
['0.000000', '0']

[sbarzowski]

Thanks for reporting. This should certainly be fixed.

[netomi]

When using the %g format, the code calculates the logarithm of the value. However, the logarithm of 0 is not defined, changing the code to this fixes the issue:

diff --git a/stdlib/std.jsonnet b/stdlib/std.jsonnet
index 960deeb..0eb2910 100644
--- a/stdlib/std.jsonnet
+++ b/stdlib/std.jsonnet
@@ -657,7 +657,11 @@ limitations under the License.
           error 'Format required number at '
                 + i + ', got ' + std.type(val)
         else
-          local exponent = std.floor(std.log(std.abs(val)) / std.log(10));
+          local exponent =
+            if val != 0 then
+              std.floor(std.log(std.abs(val)) / std.log(10))
+            else
+              0;
           if exponent < -4 || exponent >= fpprec then
             render_float_sci(val,
                              zp,

Can create a PR for it with testcases.

[netomi]

btw. the same error is present in the original jsonnet implementation, the stdlib is the same.

[netomi]

The fix in the cpp version has been merged.