[PATCH] New dpkg-source build option: --no-generate-diff

I've rebased this patch against current Git.

To recap, this option enables (re)building a source package without cross-
checking against the orig tarball, in scenarios where the latter is
superfluous and expensive. Some benchmarks from a package I work with
basically tell the story. This is with my patch applied:

$ ls -l *.orig.tar.xz 
-rw-r--r-- 1 skunk users 843547668 May 16 19:08 ungoogled-chromium_125.0.6422.60.orig.tar.xz

$ time -p dpkg-source --no-preparation --abort-on-upstream-changes --build ungoogled-chromium-src
dpkg-source.pl: info: using source format '3.0 (quilt)'
dpkg-source.pl: info: building ungoogled-chromium using existing ./ungoogled-chromium_125.0.6422.60.orig.tar.xz
dpkg-source.pl: info: using patch list from debian/patches/series
dpkg-source.pl: info: building ungoogled-chromium in ungoogled-chromium_125.0.6422.60-1xtradeb1.2204.1.debian.tar.xz
dpkg-source.pl: info: building ungoogled-chromium in ungoogled-chromium_125.0.6422.60-1xtradeb1.2204.1.dsc
real 628.93
user 198.92
sys 88.00

$ time -p dpkg-source --no-generate-diff --no-preparation --abort-on-upstream-changes --build ungoogled-chromium-src
dpkg-source.pl: info: using source format '3.0 (quilt)'
dpkg-source.pl: info: building ungoogled-chromium using existing ./ungoogled-chromium_125.0.6422.60.orig.tar.xz
dpkg-source.pl: info: building ungoogled-chromium in ungoogled-chromium_125.0.6422.60-1xtradeb1.2204.1.debian.tar.xz
dpkg-source.pl: info: building ungoogled-chromium in ungoogled-chromium_125.0.6422.60-1xtradeb1.2204.1.dsc
real 11.62
user 10.86
sys 0.74


--Daniel


---
 man/dpkg-source.pod               | 11 ++++++++++-
 scripts/Dpkg/Source/Package/V2.pm | 32 +++++++++++++++++++++++++++++---
 2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/man/dpkg-source.pod b/man/dpkg-source.pod
index 736f42fd2..4102fd986 100644
--- a/man/dpkg-source.pod
+++ b/man/dpkg-source.pod
@@ -647,7 +647,8 @@ patches have been applied during the extraction.
 
 B<Building>
 
-All original tarballs found in the current directory are extracted in a
+If B<--no-generate-diff> is not given, then
+all original tarballs found in the current directory are extracted in a
 temporary directory by following the same logic as for the unpack, the
 debian directory is copied over in the temporary directory, and all
 patches except the automatic patch (B<debian-changes->I<version>
@@ -791,6 +792,14 @@ Those options are only allowed
 in B<debian/source/local-options> so that all generated source
 packages have the same behavior by default.
 
+=item B<--no-generate-diff>
+
+Do not generate a diff against the upstream sources. This skips the process
+of extracting the original tarballs, and thus allows for a faster build.
+Not only is the source package directory not checked for any extraneous
+modifications, anything outside the debian subdirectory is ignored
+altogether. Use with caution.
+
 =item B<--abort-on-upstream-changes>
 
 The process fails if an automatic patch has been generated
diff --git a/scripts/Dpkg/Source/Package/V2.pm b/scripts/Dpkg/Source/Package/V2.pm
index 1f0946128..0eb9ba529 100644
--- a/scripts/Dpkg/Source/Package/V2.pm
+++ b/scripts/Dpkg/Source/Package/V2.pm
@@ -71,6 +71,7 @@ sub init_options {
     $self->{options}{unapply_patches} //= 'auto';
     $self->{options}{skip_debianization} //= 0;
     $self->{options}{create_empty_orig} //= 0;
+    $self->{options}{generate_diff} //= 1;
     $self->{options}{auto_commit} //= 0;
     $self->{options}{ignore_bad_version} //= 0;
 }
@@ -104,6 +105,10 @@ my @module_cmdline = (
         name => '--create-empty-orig',
         help => N_('create an empty original tarball if missing'),
         when => 'build',
+    }, {
+        name => '--no-generate-diff',
+        help => N_('do not generate diff against upstream sources'),
+        when => 'build',
     }, {
         name => '--abort-on-upstream-changes',
         help => N_('abort if generated diff has upstream files changes'),
@@ -156,6 +161,9 @@ sub parse_cmdline_option {
     } elsif ($opt eq '--create-empty-orig') {
         $self->{options}{create_empty_orig} = 1;
         return 1;
+    } elsif ($opt eq '--no-generate-diff') {
+        $self->{options}{generate_diff} = 0;
+        return 1;
     } elsif ($opt eq '--abort-on-upstream-changes') {
         $self->{options}{auto_commit} = 0;
         return 1;
@@ -460,6 +468,8 @@ sub _generate_patch {
         }
     }
 
+    return if !$opts{do_diff};
+
     # Unpack a second copy for comparison
     my $tmp = tempdir("$dirname.orig.XXXXXX", DIR => $updir);
     push_exit_handler(sub { erasedir($tmp) });
@@ -530,6 +540,21 @@ sub do_build {
         usageerr(g_("-b takes only one parameter with format '%s'"),
                  $self->{fields}{'Format'});
     }
+    if (!$self->{options}{generate_diff} &&
+        ($self->{options}{include_removal}   ||
+         $self->{options}{include_timestamp} ||
+         $self->{options}{include_binaries}  ||
+         $self->{options}{create_empty_orig} ||
+         $self->{options}{auto_commit})) {
+        my @incompat = (
+            "--include-removal",
+            "--include-timestamp",
+            "--include-binaries",
+            "--create-empty-orig",
+            "--auto-commit"
+        );
+        usageerr(g_("--no-generate-diff is incompatible with the following options: %s"), join(", ", @incompat));
+    }
     $self->prepare_build($dir);
 
     my $include_binaries = $self->{options}{include_binaries};
@@ -569,8 +594,9 @@ sub do_build {
                                         header_from => $autopatch,
                                         handle_binary => $handle_binary,
                                         skip_auto => $self->{options}{auto_commit},
+                                        do_diff => $self->{options}{generate_diff},
                                         usage => 'build');
-    unless (-z $tmpdiff or $self->{options}{auto_commit}) {
+    unless (!$tmpdiff or -z $tmpdiff or $self->{options}{auto_commit}) {
         info(g_('Hint: make sure the version in debian/changelog matches ' .
                 'the unpacked source tree'));
         info(g_('you can integrate the local changes with %s'),
@@ -578,7 +604,7 @@ sub do_build {
         error(g_('aborting due to unexpected upstream changes, see %s'),
               $tmpdiff);
     }
-    push_exit_handler(sub { unlink($tmpdiff) });
+    push_exit_handler(sub { !$tmpdiff or unlink($tmpdiff) });
     $binaryfiles->update_debian_source_include_binaries() if $include_binaries;
 
     # Install the diff as the new autopatch
@@ -590,7 +616,7 @@ sub do_build {
              $autopatch) if -e $autopatch;
         rmdir(File::Spec->catdir($dir, 'debian', 'patches')); # No check on purpose
     }
-    unlink($tmpdiff) or syserr(g_('cannot remove %s'), $tmpdiff);
+    !$tmpdiff or unlink($tmpdiff) or syserr(g_('cannot remove %s'), $tmpdiff);
     pop_exit_handler();
 
     # Create the debian.tar