Update operator yields empty object in JQ - jq

Question

I cannot understand the behaviour of the update operator of jq (version 1.6) shown in the following examples.
Why does example 1 return an updated object, but example 2 and 3 return an empty object or a wrong result?
The difference between the examples is only the calling order of the function to convert a string into a number.
#!/bin/bash
#
# strange behaviour jq
# example 1 - works as expected
jq -n '
def numberify($x): $x | tonumber? // 0;
"1" as $stringValue
| numberify($stringValue) as $intValue
# | { } # version 1: a.b does not exist yet
| { a: { b: 1 } } # version 2: a.b exists already
| .["a"] |= { b: (.b + $intValue) }
'
# result example 1, version 1 - expected
# {
# "a": {
# "b": 1
# }
# }
# result example 1, version 2 - expected
# {
# "a": {
# "b": 2
# }
# }
# example 2 - erroneous result
jq -n '
def numberify($x): $x | tonumber? // 0;
"1" as $stringValue
# | { } # version 1: a.b does not exist yet
| { a: { b: 1 } } # version 2: a.b exists already
| .["a"] |= { b: (.b + numberify($stringValue)) }
'
# result example 2, version 1 - unexpected
# {}
# result example 2, version 2 - unexpected
# {}
# example 3 - erroneous result
jq -n '
def numberify($x): $x | try tonumber catch 0;
"1" as $stringValue
# | { } # version 1: a.b does not exist yet
| { a: { b: 1 } } # version 2: a.b exists already
| .["a"] |= { b: (.b + numberify($stringValue)) }
'
# result example 3, version 1 - unexpected
# {
# "a": {
# "b": 0
# }
# }
# result example 3, version 2 - unexpected
# {
# "a": {
# "b": 1
# }
# }
#oguzismail That's a good idea to use '+=' instead of '|='.
I hadn't thought of it before.
Currently, my code with the workaround for the bug looks like this:
def numberify($x): $x | tonumber? // 0;
"1" as $sumReqSize
| "10" as $sumResSize
| { statistics: { count: 1, sumReqSize: 2, sumResSize: 20 } }
| [numberify($sumReqSize), numberify($sumResSize)] as $sizes # workaround for bug
| .statistics |= {
count: (.count + 1),
sumReqSize: (.sumReqSize + $sizes[0]),
sumResSize: (.sumResSize + $sizes[1])
}
'
Following your suggestion it will be more concise and doesn't need the ugly workaround:
def numberify($x): $x | tonumber? // 0;
"1" as $sumReqSize
| "10" as $sumResSize
| { statistics: { count: 1, sumReqSize: 2, sumResSize: 20 } }
| .statistics.count += 1
| .statistics.sumReqSize += numberify($sumReqSize)
| .statistics.sumResSize += numberify($sumResSize)

Answer 1

This is a bug in jq 1.6. One option would be to use an earlier version of jq (e.g. jq 1.5).
Another would be to avoid |= by using = instead, along the lines of:
.a = (.a | ...)
or if the RHS does not actually depend on the LHS (as in your original examples), simply replacing |= by =.

Answer 2

This is a bug in jq 1.6. In this case you can use try-catch instead.
def numberify($x): $x | try tonumber catch 0;
But I don't know if there is a generic way to walk around this issue.