inline sequences to optimize away recursive calls to make/dh for implicit targets

This assumes that all implicit rules file targets are owned by dh, so
it can just assume an implicit target can be optimized away to the commands
in its sequence.

I suppose this would break:

build:
	dh build

install: build
	dh install

binary-%: install
	my-binary-builder-$@

my-binary-builder-arch:
	echo "whee! I did something pointlessly complicated with make!"
	dh binary-arch
my-binary-builder-indep:
	dh binary-indep

But I can't imagine anyone does this, at least with a probability of 1 in
ten thousand, so hopefully it doesn't break any existing packages. :)

1 files changed, 40 insertions, 8 deletions

diff --git a/dh b/dh
index 8844fb53..33a7be33 100755
--- a/dh
+++ b/dh
@@ -550,7 +550,7 @@ if (! exists $sequences{$sequence}) {
 	error "Unknown sequence $sequence (choose from: ".
 		join(" ", sort keys %sequences).")";
 }
-my @sequence=@{$sequences{$sequence}};
+my @sequence=optimize_sequence(@{$sequences{$sequence}});
 
 # The list of all packages that can be acted on.
 my @packages=@{$dh{DOPACKAGES}};
@@ -672,18 +672,14 @@ sub run {
 	# to prevent them from being acted on.
 	push @options, map { "-N$_" } @exclude;
 
-	# If the command has a rules: prefix, run debian/rules with
-	# the remainder as the target.
-	my $rules_target = undef;
-	if ($command =~ /^rules:(.*)/) {
-		$rules_target = $1;
-	}
-
 	# Check for override targets in debian/rules and
 	# run them instead of running the command directly.
 	my $override_command;
 	my $has_explicit_target = rules_explicit_target("override_".$command);
 
+	# If the command has a rules: prefix, run debian/rules with
+	# the remainder as the target.
+	my $rules_target = rules_target($command);
 	if (defined $rules_target) {
 		# Don't pass DH_ environment variables, since this is
 		# a fresh invocation of debian/rules and any sub-dh
@@ -753,6 +749,42 @@ sub run {
 	}
 }
 
+sub optimize_sequence {
+	my @sequence;
+	my %seen;
+	my $add=sub {
+		# commands can appear multiple times when sequences are
+		# inlined together; only the first should be needed
+		my $command=shift;
+		if (! $seen{$command}) {
+			$seen{$command}=1;
+			push @sequence, $command;
+		}
+	};
+	foreach my $command (@_) {
+		my $rules_target=rules_target($command);
+		if (defined $rules_target &&
+		    ! rules_explicit_target($rules_target)) {
+			# inline the sequence for this implicit target
+			$add->($_) foreach optimize_sequence(@{$sequences{$rules_target}});
+		}
+		else {
+			$add->($command);
+		}
+	}
+	return @sequence;
+}
+
+sub rules_target {
+	my $command=shift;
+	if ($command =~ /^rules:(.*)/) {
+		return $1
+	}
+	else {
+		return undef;
+	}
+}
+
 {
 my %targets;
 my $rules_parsed;