This talk will show how it's possible to mock PerlOps using XS and provide a convenient Pure Perl hook for each of the file check -X. Overload::FileCheck provides a way to mock one or more file checks. It is also possible to mock stat/lstat functions using "mock_all_from_stat" and let Overload::FileCheck mock for you for any other -X checks.

1. The Perl Conference 2019 June 16-21
Overloading Perl OPs using XS
ℕicolas ℝ. @atoomic

2. The Perl Conference 2019 June 16-21
ℕicolas ℝ.

3. The Perl Conference 2019 June 16-21
ℕicolas ℝ. @atoomic

4. The Perl Conference 2019 June 16-21
ℕicolas ℝ. @atoomic

5. The Perl Conference 2019 June 16-21
Overloading Perl OPs using XS
ℕicolas ℝ. @atoomic

6. Overloading
Perl OPs
using XS

7. Overloading…
a.k.a. mocking

8. Overloading

9. Overloading

10. …Perl OPs…
sample OP Tree

11. Printing the OPTree - B::Terse
> perl -MO=Terse,-exec -e '$a = $b + 42’
| perl -p -e 's/(.*)//';
-e syntax OK
OP enter
COP nextstate
SVOP *b
SVOP 42
BINOP add [1]
SVOP *a
BINOP sassign
LISTOP leave [1]

12. Printing the OPTree - B::Concise
> perl -MO=Concise,-exec -e '$a = $b + 42'
1 <0> enter
2 <;> nextstate(main 1 -e:1) v:{
3 <$> gvsv(*b) s
4 <$> const(IV 42) s
5 <2> add[t1] sK/2
6 <$> gvsv(*a) s
7 <2> sassign vKS/2
8 <@> leave[1 ref] vKP/REFC
-e syntax OK

13. Perl OPs
> perl -MO=Concise,-exec -e '$f'
1 <0> enter
2 <;> nextstate(main 1 -e:1) v:{
3 <$> gvsv(*f) s
4 <1> srefgen vK/1
5 <@> leave[1 ref] vKP/REFC

14. Perl OPs - opnames.h

15. Perl OPs: opcode.h

16. PP ?
Push / Pop
pp ("push/pop") functions execute the opcodes
A typical pp function
- expects to find its arguments on the stack,
- and usually pushes its results onto the stack,
- hence the 'pp' terminology.
- Each OP structure contains a pointer to the relevant pp_foo() function.

17. Perl_PP_ ?
> grep 'PP(' pp.c | sort | head
PP(pp_abs)
PP(pp_aeach)
PP(pp_akeys)
PP(pp_anoncode)
PP(pp_anonconst)
PP(pp_anonhash)
PP(pp_anonlist)
PP(pp_argcheck)
PP(pp_argdefelem)
PP(pp_argelem)

18. Perl_PP_ ?

19. Perl OPs
> perl -MO=Concise,-exec -e '$f'
1 <0> enter
2 <;> nextstate(main 1 -e:1) v:{
3 <$> gvsv(*f) s
4 <1> srefgen vK/1
5 <@> leave[1 ref] vKP/REFC

20. Perl OPs
> perl -MO=Concise,-exec -e '$f'
1 <0> enter
2 <;> nextstate(main 1 -e:1) v:{
3 <$> gvsv(*f) s
4 <1> srefgen vK/1
5 <@> leave[1 ref] vKP/REFC

21. Overloading
Perl OPs…

22. …using XS
the glue between C and Perl API

23. Overloading Perl OPs using XS
Why ? Why ? Why ? Why ? Why ?

24. OP_DIE
pp_sys.c:456:PP(pp_die)
opnames.h:209: OP_DIE = 192,
*GLOBAL::CORE::die

25. OP_DIE
> perl die.pl
This is the end at die.pl line 8.

26. OP_DIE
> perl -MO=Terse,-exec die.pl | perl -pe ’s/(.*)/t/'
OP enter
COP nextstate
LOOP enterloop
REDO =>
COP nextstate
SVOP
UNOP srefgen
SVOP *CORE::GLOBAL::die
UNOP rv2gv
BINOP sassign
LAST =>
BINOP leaveloop
COP nextstate
OP pushmark
SVOP "This is the end"
LISTOP die [2]
COP nextstate
OP pushmark
SVOP "...or not"
LISTOP say
LISTOP leave [1]

27. OP_DIE
> perl die.pl
Still Alive...
...or not

28. OP_DIE
> perl -MO=Terse,-exec die.pl | perl -pe ’s/(.*)/t/'
OP enter
COP nextstate
OP pushmark
SVOP "This is the end"
SVOP *CORE::GLOBAL::die
UNOP entersub
COP nextstate
OP pushmark
SVOP "...or not"
LISTOP say
LISTOP leave [1]

29. Not all OPs can be mocked using
CORE::GLOBAL::*
How to mock ‘-e’? -X?

30. Not all OPs can be mocked using
CORE::GLOBAL::*

31. Overloading `-e` check
github.com/atoomic/Overload-FileCheck/tree/demo
Code Demo

32. -r File is readable by effective uid/gid.
-w File is writable by effective uid/gid.
-x File is executable by effective uid/gid.
-o File is owned by effective uid.
-R File is readable by real uid/gid.
-W File is writable by real uid/gid.
-X File is executable by real uid/gid.
-O File is owned by real uid.
-e File exists.
-z File has zero size (is empty).
-s File has nonzero size (returns size in bytes).
-f File is a plain file.
-d File is a directory.
-l File is a symbolic link (false if symlinks aren't
supported by the file system).
-p File is a named pipe (FIFO), or Filehandle is a pipe.
-S File is a socket.
-b File is a block special file.
-c File is a character special file.
-t Filehandle is opened to a tty.
-u File has setuid bit set.
-g File has setgid bit set.
-k File has sticky bit set.
-T File is an ASCII or UTF-8 text file (heuristic guess).
-B File is a "binary" file (opposite of -T).
-M Script start time minus file modification time, in days.
-A Same for access time.
-C Same for inode change time
> perldoc -f -X
perldoc.perl.org/functions/-X.html
Overload::FileCheck -X

33. Overload::FileCheck -X
-r -w -x -o -R -W -X
-O -e -z -s -f -d -l -p
-S -b -c -t -u -g -k
-T -B -M -A -C
* boolean / integer
* using stat
* stat($f) && -e _

34. Overload::FileCheck
github.com/atoomic/Slides-Overload-FileCheck
Bonus Slides

35. slides…

36. Test::MockFile -Todd Rinaldo
use Test::MockFile;
# Be sure to assign the output of mocks / scoped
my $mock_file = Test::MockFile->file(
"/foo/bar", “contents"
);
# Does not actually open the file on disk.
open( my $fh, "<", “/foo/bar" ) or die;
say "ok" if -e $fh;
close $fh;
say "ok" if -e "/foo/bar";

37. Test::MockFile strict mode
use Test::MockFile qw/strict/;
# This will not die.
my $file = Test::MockFile->file("/bar", "...");
my $symlink = Test::MockFile->symlink("/foo", "/bar");
-l "/foo" or print "okn";
open(my $fh, ">", "/foo");
# All of these will die
open(my $fh, ">", "/unmocked/file"); # Dies
sysopen(my $fh, "/other/file", O_RDONLY);
opendir(my $fh, "/dir");
-e "/file";
-l "/file"

38. ✤ better knowledge of PerlOPs
✤ mocking filesystem for testing
✤ B::C Lazy OPs
✤ B::C Lazy RegExp
✤ p5p improvement for CV
Lessons learned

39. The Perl Conference 2019 June 16-21
Images: Pixabay License, free for commercial use
Overloading Perl OPs using XS
ℕicolas ℝ.
@atoomic
thank you