Perl v5.26 can now detect and warn you about a version control conflict markers in your code. In prior versions, the compiler would try to interpret those as code and would complain about a syntax error. You program still fails to compile but you get a better error message. Maybe some future Perl will bifurcate the program, run both versions, and compare the results (don’t hold your breath):
To demonstrate this, set up a new git repository, create a simple “Hello World” program, and commit it:
$ mkdir test-repo; cd test_repo; git init Initialized empty Git repository in /Users/buster/test_repo/.git/ $ cat > hello.pl #!/usr/bin/perl use v5.10; say "Hello World!"; ^D $ git add hello.pl $ git commit -a -m 'initial program' [master (root-commit) 0665c2b] initial program 1 file changed, 3 insertions(+) create mode 100755 hello.pl
Now that you have the file you need to create a conflict that Perl can detect. One way is to edit in a new branch and the master branch at the same time.
$ git checkout -b new_feature Switched to a new branch 'new_feature' $ cat > hello.pl #!/usr/bin/perl use v5.10; say "Hello Perl 5.26!"; $ git commit -a -m 'Greet the new perl' [new_feature 9ed328a] Greet the new perl 1 file changed, 1 insertion(+), 1 deletion(-) $ git checkout master Switched to branch 'master' $ cat > hello.pl #!/usr/bin/perl use v5.10; say "Hello new Perl!"; $ git commit -a -m 'Greet the new Perl' [master 15dd6ac] Greet the new Perl 1 file changed, 1 insertion(+), 1 deletion(-)
Both of these programs change the message in the say statement. Both commits have a similar message (that’s not important). You can pull from a branch to try to merge it into your current branch. You may get the same thing by pulling from a remote where someone else was working on the same file as you. The merge gives you a warning:
$ git pull . new_feature From . * branch new_feature -> FETCH_HEAD Auto-merging hello.pl CONFLICT (content): Merge conflict in hello.pl Automatic merge failed; fix conflicts and then commit the result.
The file now has both versions of the file. A git conflict marker starts with <<<<<<<. That’s followed by the version for file as it exists in the current branch. The ends with =======, after which is the content for the incoming version. Finally, the end of the conflict is denoted with >>>>>>> and the commit digest for the incoming commit marked as HEAD (you know the current commit because, well, it’s the current commit: git show -s --format=%H):
$ cat hello.pl #!/usr/bin/perl use v5.10; <<<<<<< HEAD say "Hello new Perl!"; ======= say "Hello Perl 5.26!"; >>>>>>> 9ed328a5468aeab03098a4ded7a6bbc6daf8ac61
Versions prior to v5.26 give an odd error that doesn’t seem to relate to anything going on in the program. Earlier Perls think you are trying to use a heredoc:
$ perl5.24 hello.pl Use of bare << to mean <<"" is deprecated at hello.pl line 3.
Now the error message better detects what’s going on:
$ perl5.26 hello.pl Version control conflict marker at hello.pl line 3, near "<<<<<<<" Version control conflict marker at hello.pl line 5, near "=======" Version control conflict marker at hello.pl line 7, near ">>>>>>>" Execution of hello.pl aborted due to compilation errors.
Running it under diagnostics gives extra information (although it’s not always much more helpful):
$ perl -Mdiagnostics hello.pl
Version control conflict marker at hello.pl line 3, near "<<<<<<<"
Version control conflict marker at hello.pl line 5, near "======="
Version control conflict marker at hello.pl line 7, near ">>>>>>>"
Execution of hello.pl aborted due to compilation errors (#1)
(F) The parser found a line starting with <<<<<<<,
>>>>>>>, or =======. These may be left by a
version control system to mark conflicts after a failed merge operation.
Uncaught exception from user code:
Version control conflict marker at hello.pl line 3, near "<<<<<<<"
Version control conflict marker at hello.pl line 5, near "======="
Version control conflict marker at hello.pl line 7, near ">>>>>>>"
Execution of hello.pl aborted due to compilation errors.