perl Git::LoadCPAN: emit better errors under NO_PERL_CPAN_FALLBACKS

Before my 20d2a30f8f ("Makefile: replace perl/Makefile.PL with simple
make rules", 2017-12-10) on an OS package that removed the
private-Error.pm copy we carried around manually removing the OS's
Error.pm would yield:

$ git add -p
Can't locate Error.pm in @INC (you may need to install the Error module) [...]

Now, before this change we'll instead emit this more cryptic error:

$ git add -p
BUG: '/usr/share/perl5/Git/FromCPAN' should be a directory! at /usr/share/perl5/Git/Error.pm line 36.

This is a confusing error. Now if the new NO_PERL_CPAN_FALLBACKS
option is specified and we can't find the module we'll instead emit:

$ /tmp/git/bin/git add -p
BUG: The 'Error' module is not here, but NO_PERL_CPAN_FALLBACKS was set!

[...]

Where [...] is the lengthy explanation seen in the change below, which
explains what the potential breakage is, and how to fix it.

The reason for checking @@NO_PERL_CPAN_FALLBACKS@@] against the empty
string in Perl is as opposed to checking for a boolean value is that
that's (as far as I can tell) make's idea of a string that's set, and
e.g. NO_PERL_CPAN_FALLBACKS=0 is enough to set NO_PERL_CPAN_FALLBACKS.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/INSTALL b/INSTALL
index 808e07b6599476afc8a0b3a385e73df8b7f9c63d..60e515eaf7432e77d8db8837b7bb95e105ca2126 100644 (file)
--- a/INSTALL
+++ b/INSTALL
@@ -88,9 +88,9 @@ Issues of note:
        export GIT_EXEC_PATH PATH GITPERLLIB
 
  - By default (unless NO_PERL is provided) Git will ship various perl
        export GIT_EXEC_PATH PATH GITPERLLIB
 
  - By default (unless NO_PERL is provided) Git will ship various perl

-   scripts & libraries it needs. However, for simplicity it doesn't
-   use the ExtUtils::MakeMaker toolchain to decide where to place the
-   perl libraries. Depending on the system this can result in the perl
+   scripts. However, for simplicity it doesn't use the
+   ExtUtils::MakeMaker toolchain to decide where to place the perl
+   libraries. Depending on the system this can result in the perl

    libraries not being where you'd like them if they're expected to be
    used by things other than Git itself.
 
    libraries not being where you'd like them if they're expected to be
    used by things other than Git itself.
 


@@ -102,6 +102,11 @@ Issues of note:
    Will result in e.g. perllibdir=/usr/share/perl/5.26.1 on Debian,
    perllibdir=/usr/share/perl5 (which we'd use by default) on CentOS.
 
    Will result in e.g. perllibdir=/usr/share/perl/5.26.1 on Debian,
    perllibdir=/usr/share/perl5 (which we'd use by default) on CentOS.
 

+ - Unless NO_PERL is provided Git will ship various perl libraries it
+   needs. Distributors of Git will usually want to set
+   NO_PERL_CPAN_FALLBACKS if NO_PERL is not provided to use their own
+   copies of the CPAN modules Git needs.
+

  - Git is reasonably self-sufficient, but does depend on a few external
    programs and libraries.  Git can be used without most of them by adding
    the approriate "NO_<LIBRARY>=YesPlease" to the make command line or
  - Git is reasonably self-sufficient, but does depend on a few external
    programs and libraries.  Git can be used without most of them by adding
    the approriate "NO_<LIBRARY>=YesPlease" to the make command line or

diff --git a/Makefile b/Makefile
index 518c5f6be057cc7d864465b6214019e8ceabca32..4e0cdb3ca4a3c722c12b7219c72c978dddac45bd 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -2314,11 +2314,14 @@ all:: $(LIB_PERL_GEN)
 ifndef NO_PERL_CPAN_FALLBACKS
 all:: $(LIB_CPAN_GEN)
 endif
 ifndef NO_PERL_CPAN_FALLBACKS
 all:: $(LIB_CPAN_GEN)
 endif

+NO_PERL_CPAN_FALLBACKS_SQ = $(subst ','\'',$(NO_PERL_CPAN_FALLBACKS))

 endif
 
 perl/build/lib/%.pm: perl/%.pm
        $(QUIET_GEN)mkdir -p $(dir $@) && \
 endif
 
 perl/build/lib/%.pm: perl/%.pm
        $(QUIET_GEN)mkdir -p $(dir $@) && \

-       sed -e 's|@@LOCALEDIR@@|$(localedir_SQ)|g' < $< > $@
+       sed -e 's|@@LOCALEDIR@@|$(localedir_SQ)|g' \
+           -e 's|@@NO_PERL_CPAN_FALLBACKS@@|$(NO_PERL_CPAN_FALLBACKS_SQ)|g' \
+       < $< > $@

 
 perl/build/man/man3/Git.3pm: perl/Git.pm
        $(QUIET_GEN)mkdir -p $(dir $@) && \
 
 perl/build/man/man3/Git.3pm: perl/Git.pm
        $(QUIET_GEN)mkdir -p $(dir $@) && \

diff --git a/perl/Git/LoadCPAN.pm b/perl/Git/LoadCPAN.pm
index 229c1ee87d34387ca3f4b8dffdc7b6fe74f04f1e..e5585e75e809ef5763d3d4f19ebd185c6f7c0f51 100644 (file)
--- a/perl/Git/LoadCPAN.pm
+++ b/perl/Git/LoadCPAN.pm
@@ -19,13 +19,25 @@ =head1 DESCRIPTION
 will fall back on C<FromCPAN::Module::Name> shipped with Git itself.
 
 Usually distributors will not ship with Git's Git::FromCPAN tree at
 will fall back on C<FromCPAN::Module::Name> shipped with Git itself.
 
 Usually distributors will not ship with Git's Git::FromCPAN tree at

-all, preferring to use their own packaging of CPAN modules instead.
+all via the C<NO_PERL_CPAN_FALLBACKS> option, preferring to use their
+own packaging of CPAN modules instead.

 
 This module is only intended to be used for code shipping in the
 C<git.git> repository. Use it for anything else at your peril!
 
 =cut
 
 
 This module is only intended to be used for code shipping in the
 C<git.git> repository. Use it for anything else at your peril!
 
 =cut
 

+# NO_PERL_CPAN_FALLBACKS_STR evades the sed search-replace from the
+# Makefile, and allows for detecting whether the module is loaded from
+# perl/Git as opposed to perl/build/Git, which is useful for one-off
+# testing without having Error.pm et al installed.
+use constant NO_PERL_CPAN_FALLBACKS_STR => '@@' . 'NO_PERL_CPAN_FALLBACKS' . '@@';
+use constant NO_PERL_CPAN_FALLBACKS => (
+       q[@@NO_PERL_CPAN_FALLBACKS@@] ne ''
+       and
+       q[@@NO_PERL_CPAN_FALLBACKS@@] ne NO_PERL_CPAN_FALLBACKS_STR
+);
+

 sub import {
        shift;
        my $caller = caller;
 sub import {
        shift;
        my $caller = caller;


@@ -45,6 +57,25 @@ sub import {
        } or do {
                my $error = $@ || "Zombie Error";
 
        } or do {
                my $error = $@ || "Zombie Error";
 

+               if (NO_PERL_CPAN_FALLBACKS) {
+                       chomp(my $error = sprintf <<'THEY_PROMISED', $module);
+BUG: The '%s' module is not here, but NO_PERL_CPAN_FALLBACKS was set!
+
+Git needs this Perl module from the CPAN, and will by default ship
+with a copy of it. This Git was built with NO_PERL_CPAN_FALLBACKS,
+meaning that whoever built it promised to provide this module.
+
+You're seeing this error because they broke that promise, and we can't
+load our fallback version, since we were asked not to install it.
+
+If you're seeing this error and didn't package Git yourself the
+package you're using is broken, or your system is broken. This error
+won't appear if Git is built without NO_PERL_CPAN_FALLBACKS (instead
+we'll use our fallback version of the module).
+THEY_PROMISED
+                       die $error;
+               }
+

                my $Git_LoadCPAN_pm_path = $INC{"Git/LoadCPAN.pm"} || die "BUG: Should have our own path from %INC!";
 
                require File::Basename;
                my $Git_LoadCPAN_pm_path = $INC{"Git/LoadCPAN.pm"} || die "BUG: Should have our own path from %INC!";
 
                require File::Basename;