git-debrebase: Provide new convert-from-dgit-view operation.

The output is, unavoidably, not very pretty.

Closes:#905322.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

3 files changed, 256 insertions, 0 deletions

diff --git a/debian/changelog b/debian/changelog
index a64a06d..fd3f102 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -8,6 +8,8 @@ dgit (6.5~) unstable; urgency=medium
   * git-debrebase: Properly reject bare dgit dsc imports
   * git-debrebase: Improve some error message formatting.
   * test suite: gdr-import-dgitview: New test for dgit dsc imports.
+  * git-debrebase: Provide new convert-from-dgit-view operation.
+    The output is, unavoidably, not very pretty.  Closes:#905322.
 
  --
 
diff --git a/git-debrebase b/git-debrebase
index b51c714..98e645a 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -1788,6 +1788,194 @@ git-debrebase: WARNING: doing so would drop all upstream patches!
 END
 }
 
+sub cmd_convert_from_dgit_view () { 
+    my $clogp = parsechangelog();
+
+    my $bpd = (cfg 'dgit.default.build-products-dir',1) // '..';
+    my $do_origs = 1;
+    my $do_tags = 1;
+    my $always = 0;
+    my $diagnose = 0;
+
+    getoptions("convert-from-dgit-view",
+	       'diagnose!', \$diagnose,
+	       'build-products-dir:s', \$bpd,
+	       'origs!', \$do_origs,
+	       'tags!', \$do_tags,
+	       'always-convert-anyway!', \$always);
+    fail "takes 1 optional argument, the upstream commitish" if @ARGV>1;
+
+    my @upstreams;
+
+    if (@ARGV) {
+	my $spec = shift @ARGV;
+	my $commit = git_rev_parse "$spec^{commit}";
+	push @upstreams, { Commit => $commit,
+			   Source => "$ARGV[0], from command line",
+			   Only => 1,
+			 };
+    }
+
+    my $head = get_head();
+
+    if (!$always) {
+	my $troubles = 0;
+	my $trouble = sub { $troubles++; };
+	keycommits $head, sub{}, sub{}, $trouble, $trouble;
+	printdebug "troubles=$troubles\n";
+	if (!$troubles) {
+	    print STDERR <<END;
+$us: Branch already seems to be in git-debrebase format!
+$us: --always-convert-anyway would do the conversion operation anyway
+$us: but is probably a bad idea.  Probably, you wanted to do nothing.
+END
+	    fail "Branch already in git-debrebase format." unless $opt_noop_ok;
+	    finish 0;
+	}
+    }
+
+    snags_maybe_bail_early();
+
+    my $version = upstreamversion $clogp->{Version};
+    print STDERR "Considering possible commits corresponding to upstream:\n";
+
+    if (!@upstreams) {
+	if ($do_tags) {
+	    my @tried;
+	    my $ups_tag = upstream_commitish_search $version, \@tried;
+	    if ($ups_tag) {
+		my $this = "git tag $tried[-1]";
+		push @upstreams, { Commit => $ups_tag,
+				   Source => $this,
+				 };
+	    } else {
+		printf STDERR
+		    " git tag: no suitable tag found (tried %s)\n",
+		    "@tried";
+	    }
+	}
+	if ($do_origs) {
+	    my $p = $clogp->{'Source'};
+	    # we do a quick check to see if there are plausible origs
+	    my $something=0;
+	    if (!opendir BPD, $bpd) {
+		die "$bpd: opendir: $!" unless $!==ENOENT;
+	    } else {
+		while ($!=0, my $f = readdir BPD) {
+		    next unless is_orig_file_of_p_v $f, $p, $version;
+		    printf STDERR
+			" orig: found what looks like a .orig, %s\n",
+			"$bpd/$f";
+		    $something=1;
+		    last;
+		}
+		die "read $bpd: $!" if $!;
+		closedir BPD;
+	    }
+	    if ($something) {
+		my $tree = cmdoutput
+		    @dgit, qw(--build-products-dir), $bpd,
+		    qw(print-unapplied-treeish);
+		fresh_workarea();
+		in_workarea sub {
+		    runcmd @git, qw(reset --quiet), $tree, qw(-- .);
+		    rm_subdir_cached 'debian';
+		    $tree = cmdoutput @git, qw(write-tree);
+		    my $ups_synth = make_commit [], [ <<END, <<END,
+Import effective orig tree for upstream version $version
+END
+This includes the contents of the .orig(s), minus any debian/ directory.
+
+[git-debrebase import-from-dgit-view upstream-import-convert: $version]
+END
+						    ];
+		    push @upstreams, { Commit => $ups_synth,
+				       Source => "orig(s) imported via dgit",
+				     };
+		}
+	    } else {
+		printf STDERR
+		    " orig: no suitable origs found (looked for %s in %s)\n",
+		    "${p}_".(stripeoch $version)."...", $bpd;
+	    }
+	}
+    }
+
+    my $some_patches = stat_exists 'debian/patches/series';
+
+    print STDERR "Evaluating possible commits corresponding to upstream:\n";
+
+    my $result;
+    foreach my $u (@upstreams) {
+	my $work = $head;
+	fresh_workarea();
+	in_workarea sub {
+	    runcmd @git, qw(reset --quiet), $u->{Commit}, qw(-- .);
+	    runcmd @git, qw(checkout), $u->{Commit}, qw(-- .);
+	    runcmd @git, qw(clean -xdff);
+	    runcmd @git, qw(checkout), $head, qw(-- debian);
+	    if ($some_patches) {
+		rm_subdir_cached 'debian/patches';
+		$work = make_commit [ $work ], [
+ 'git-debrebase convert-from-dgit-view: drop upstream changes from breakwater',
+ "Drop upstream changes, and delete debian/patches, as part of converting\n".
+ "to git-debrebase format.  Upstream changes will appear as commits.",
+ '[git-debrebase convert-from-dgit-view: drop patches from tree]'
+					   ];
+	    }
+	    $work = make_commit [ $work, $u->{Commit} ], [
+ 'git-debrebase convert-from-dgit-view: declare upstream',
+ '(Re)constructed breakwater merge.',
+ '[git-debrebase anchor: declare upstream]'
+							 ];
+	    runcmd @git, qw(checkout --quiet -b mk), $work;
+	    if ($some_patches) {
+		runcmd @git, qw(checkout), $head, qw(-- debian/patches);
+		runcmd @git, qw(reset --quiet);
+		my @gbp_cmd = (qw(gbp pq import));
+		if (!$diagnose) {
+		    my $gbp_err = "../gbp-pq-err";
+		    @gbp_cmd = shell_cmd "exec >$gbp_err 2>&1", @gbp_cmd;
+		}
+		my $r = system @gbp_cmd;
+		if ($r) {
+		    printf STDERR
+			" %s: couldn't apply patches: gbp pq %s",
+			$u->{Source}, waitstatusmsg();
+		    return;
+		}
+	    }
+	    my $work = git_rev_parse qw(HEAD);
+	    my $diffout = cmdoutput @git, qw(diff-tree --stat HEAD), $work;
+	    if (length $diffout) {
+		print STDERR
+		    " $u->{Source}: applying patches gives different tree\n";
+		print STDERR $diffout if $diagnose;
+		return;
+	    }
+	    # OMG!
+	    $u->{Result} = $work;
+	    $result = $u;
+	};
+	last if $result;
+    }
+
+    if (!$result) {
+	fail <<END;
+Could not find or construct a suitable upstream commit.
+Rerun adding --diagnose after convert-from-dgit-view, or pass a
+upstream commmit explicitly or provide suitable origs.
+END
+    }
+
+    printf STDERR "Yes, will base new branch on %s\n", $result->{Source};
+
+    ffq_check $result->{Result};
+    snags_maybe_bail();
+    update_head_checkout $head, $result->{Result},
+	'convert-from-dgit-view';
+}
+
 sub cmd_downstream_rebase_launder_v0 () {
     badusage "needs 1 argument, the baseline" unless @ARGV==1;
     my ($base) = @ARGV;
diff --git a/git-debrebase.1.pod b/git-debrebase.1.pod
index eb85c6c..e544a8c 100644
--- a/git-debrebase.1.pod
+++ b/git-debrebase.1.pod
@@ -343,6 +343,72 @@ Be sure to not accidentally treat the result as
 a git-debrebase branch,
 or you will drop all the patches!
 
+=item git-debrebase convert-from-dgit-view [<convert-options>] [upstream]
+
+Converts any dgit-compatible git branch
+corresponding to a (possibly hypothetical) 3.0 quilt dsc source package
+into a git-debrebase-compatible branch.
+
+This operation should not be used
+if the branch is already in git-debrebase form.
+Normally git-debrebase will refuse to continue in this case
+(or silently do nothing if the global --noop-ok option is used).
+
+Some representation of the original upstream source code will be needed.
+If I<upstream> is supplied, that must be a suitable upstream commit.
+By default,
+git-debrebase will look first for git tags (as for new-upstream),
+and then for orig tarballs which it will ask dgit to process.
+
+The upstream source must be exactly right and
+all the patches in debian/patches must be up to date.
+Applying the patches from debian/patches to the upstream source
+must result in exactly your HEAD.
+
+The output is laundered and stitched.
+The resulting history is not particularly pretty,
+especially if orig tarball(s) were imported
+to produce a synthetic upstream commit.
+
+The available convert-options are as follows.
+(These must come after convert-from-dgit-view.)
+
+=over
+
+=item --[no-]diagnose
+
+Print additional error messages to help diagnose
+failure to find an appropriate upstream.
+--no-diagnose is the default.
+
+=item --build-products-dir
+
+Directory to look in for orig tarballs.
+The default is the git config option
+dgit.default.build-products-dir
+or failing that, C<..>.
+Passed on to dgit, if git-debrebase invokes dgit.
+
+=item --[no-]origs
+
+Whether to try to look for or use any orig tarballs.
+--origs is the default.
+
+=item --[no-]tags
+
+Whether to try to look for or use any upstream git tags.
+--tags is the default.
+
+=item --always-convert-anyway
+
+Perform the conversion operation,
+producing unpleasant extra history,
+even if the branch seems to be in git-debrebase form already.
+This should not be done unless necessary,
+and it should not be necessary.
+
+=back
+
 =back
 
 =head1 OPTIONS