Re: [HACKERS] Failure in commit_ts tap tests - Mailing list pgsql-hackers

On Sat, Jan 21, 2017 at 9:39 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

Pavan Deolasee <pavan.deolasee@gmail.com> writes:
> On Sat, Jan 21, 2017 at 9:09 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Hm, but what of the "null" value?  Also, I get
>>
>> $ perl -e 'use warnings; use Test::More; ok("2017-01-01" != "null", "ok");'
>> Argument "null" isn't numeric in numeric ne (!=) at -e line 1.
>> Argument "2017-01-01" isn't numeric in numeric ne (!=) at -e line 1.
>> ok 1 - ok

> It declares the test as "passed", right?

Oh!  So it does.  That is one darn weird behavior of the != operator.

Indeed! See this:

# first numeric matches, doesn't check beyond that

$ perl -e 'if ("2017-23" != "2017-24") {print "Not equal\n"} else {print "Equal\n"}'

Equal

# first numeric doesn't match, operators works ok

$ perl -e 'if ("2017-23" != "2018-24") {print "Not equal\n"} else {print "Equal\n"}'

Not equal

# comparison of numeric with non-numeric, works ok

$ perl -e 'if ("2017-23" != "Foo") {print "Not equal\n"} else {print "Equal\n"}'

Not equal

# numeric on RHS, works ok

$ perl -e 'if ("Foo" != "2018-24") {print "Not equal\n"} else {print "Equal\n"}'

Not equal

These tests show that the operator returns the correct result it finds a numeric value at the start of the string, either on LHS or RHS. Also, it will only compare the numeric values until first non-numeric character is found.

# no numeric on either side

$ perl -e 'if ("Fri 2017-23" != "Fri 2017-23") {print "Not equal\n"} else {print "Equal\n"}'

Equal

# no numeric on either side, arbitrary strings declared as equal

$ perl -e 'if ("Fri 2017-23" != "Foo") {print "Not equal\n"} else {print "Equal\n"}'

Equal

These two tests show why we saw no failure earlier. If neither LHS or RHS string has a starting numeric value, the operator declares the arguments as equal, irrespective of their values. I tested the same with == operator and that also exhibits the same behaviour. Weird and I wonder how it's not a source of constant bugs in perl code (I don't use perl a lot, so may be those who do are used to either turning warnings on or know this already.

 

There's still the point that we're not actually exercising this script
in the buildfarm ...

Yes indeed.

Thanks,

Pavan

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 Pavan Deolasee                   http://www.2ndQuadrant.com/
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