Bug #17205: Misleading error message when comparing NaN with numbers in array

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.0.0dev (2020-09-30T11:43:19Z master 65e8a29389) [x86_64-darwin19]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

[timhwang21 (Tim Hwang)]

The closest issue I could find is this: https://bugs.ruby-lang.org/issues/10424

There is quite a lot of inconsistency when dealing with arrays containing NaN, dependent on 1) if comparing against an integer or a float, 2) order of comparison. The one that stands out to me as "least correct" is the last one ([Float::NAN, 1.0].min) which raises TypeError (no implicit conversion from nil to integer).

# .sort
[1, Float::NAN].sort
# Most sensible error message
# ArgumentError (comparison of Integer with NaN failed)

[1.0, Float::NAN].sort
# Somewhat sensible error message
# TypeError (no implicit conversion from nil to integer)

[Float::NAN, 1].sort
# Somewhat sensible error message
# TypeError (no implicit conversion from nil to integer)

[Float::NAN, 1.0].sort
# Somewhat sensible error message
# TypeError (no implicit conversion from nil to integer)

# .min
[1, Float::NAN].min
# Most sensible error message
# ArgumentError (comparison of Float with 1 failed)

[1.0, Float::NAN].min
# Somewhat sensible error message
# TypeError (no implicit conversion from nil to integer)

[Float::NAN, 1].min
# Most sensible error message
# ArgumentError (comparison of Integer with NaN failed)

[Float::NAN, 1.0].min
# Very misleading error message
# TypeError (no implicit conversion from nil to integer)

[timhwang21 (Tim Hwang)]

The closest issue I could find is this: https://bugs.ruby-lang.org/issues/10424

There is quite a lot of inconsistency when dealing with arrays containing NaN, dependent on 1) if comparing against an integer or a float, 2) order of comparison. The one that stands out to me as "least correct" is the last one ([Float::NAN, 1.0].min) which raises TypeError (no implicit conversion from nil to integer).

# .sort
[1, Float::NAN].sort
# Most sensible error message
# ArgumentError (comparison of Integer with NaN failed)

[1.0, Float::NAN].sort
# Confusing error message
# TypeError (no implicit conversion from nil to integer)

[Float::NAN, 1].sort
# Confusing error message
# TypeError (no implicit conversion from nil to integer)

[Float::NAN, 1.0].sort
# Confusing error message
# TypeError (no implicit conversion from nil to integer)

# .min
[1, Float::NAN].min
# Most sensible error message
# ArgumentError (comparison of Float with 1 failed)

[1.0, Float::NAN].min
# Confusing error message
# TypeError (no implicit conversion from nil to integer)

[Float::NAN, 1].min
# Most sensible error message
# ArgumentError (comparison of Integer with NaN failed)

[Float::NAN, 1.0].min
# Confusing error message
# TypeError (no implicit conversion from nil to integer)

[shyouhei (Shyouhei Urabe)]

JFYI the reason why "implicit conversion from nil to integer" happens:

zsh % LC_ALL=C gdb --args ./miniruby -e'[Float::NAN, 1.0].min'
GNU gdb (Ubuntu 8.2-0ubuntu1~18.04) 8.2
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./miniruby...done.
(gdb) break rb_raise
Breakpoint 1 at 0xc4520: file error.c, line 2824.
(gdb) run
Starting program: ./miniruby -e\[Float::NAN,\ 1.0\].min
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Breakpoint 1, rb_raise (exc=93824999143280, fmt=fmt@entry=0x55555583a928 "no implicit conversion from nil to integer") at error.c:2824
2824    {
(gdb) bt
#0  rb_raise (exc=93824999143280, fmt=fmt@entry=0x55555583a928 "no implicit conversion from nil to integer") at error.c:2824
#1  0x00005555556c9421 in rb_num2long (val=<optimized out>) at numeric.c:2885
#2  0x00005555556ca28e in rb_num2int (val=<optimized out>) at numeric.c:2989
#3  rb_num2int_inline (x=<optimized out>) at include/ruby/internal/arithmetic/int.h:95
#4  rb_float_cmp (x=18410715276690587650, y=<optimized out>) at numeric.c:1521
#5  0x0000555555803fa9 in vm_opt_newarray_min (ptr=<optimized out>, num=<optimized out>) at vm_method.c:2293
#6  vm_exec_core (ec=0x555555beb770, initial=93824995273000) at insns.def:863
#7  0x00005555557f4f90 in rb_vm_exec (ec=0x555555b3f5b0, mjit_enable_p=1) at vm.c:1983
#8  0x000055555561b940 in rb_ec_exec_node (ec=ec@entry=0x555555b3f5b0, n=n@entry=0x555555b63dc0) at eval.c:308
#9  0x000055555561fef7 in ruby_run_node (n=0x555555b63dc0) at eval.c:366
#10 0x000055555558165f in main (argc=<optimized out>, argv=<optimized out>) at main.c:50
(gdb)

I guess this is a bug of rb_float_cmp().

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset git|89ca842dcce7f05942e2d7be3edc404c9556cafd.

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Ensure that the comparison succeeded [Bug #17205]