scripts/package-metadata.pl: inhibit compile deps on missing build types

When a package declares a PKG_BUILD_DEPENDENCY or HOST_BUILD_DEPENDENCY on
a not existing build type, the metadata script will emit a reference to an
unresolvable build target in tmp/.packagedeps, causing the make process to
fail hard in a way not catchable by the IGNORE_ERRORS mechanism.

In a situation where a package "test-a" declares a build dependency
"PKG_BUILD_DEPENDS:=test-b/host" while the Makefile of "test-b" does not
implement a HostBuild, make fails with an unrecoverable error in the form:

    make[1]: Entering directory '...'
    make[1]: *** No rule to make target 'package/test-b/host/compile',
                 needed by 'package/test-a/compile'.  Stop.
    make[1]: Leaving directory '...'
    .../toplevel.mk:200: recipe for target 'package/test-a/compile' failed
    make: *** [package/test-a/compile] Error 2

Extend the metadata generation script to catch such unresolved references
and emit a visable warning upon detection.

After this change, the script will emit a warning similar to:

    WARNING: Makefile "package/test-a/Makefile" has a build dependency on
    "test-b/host" but "package/test-b/Makefile" does not implement a
    "host" build type

Fixes a global build cluster outage which occured after the "python-cffi"
feed package removed its HostBuild which the "python-cryptography" package
build-depended on.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

scripts/package-metadata.pl

@@ -460,20 +460,27 @@ sub gen_package_mk() {
 			next unless $pkg->{"builddepends/$type"};
 			foreach my $dep (@{$pkg->{"builddepends/$type"}}) {
 				my $suffix = "";
+				my $deptype = "";
 				my $condition;
 
 				if ($dep =~ /^(.+):(.+)/) {
 					$condition = $1;
 					$dep = $2;
 				}
-				if ($dep =~ /^(.+)(\/.+)/) {
+				if ($dep =~ /^(.+)\/(.+)/) {
 					$dep = $1;
-					$suffix = $2;
+					$deptype = $2;
+					$suffix = "/$2";
 				}
 
 				my $idx = "";
 				my $pkg_dep = $package{$dep};
 				if (defined($pkg_dep) && defined($pkg_dep->{src})) {
+					unless (!$deptype || grep { $_ eq $deptype } @{$pkg_dep->{buildtypes}}) {
+						warn sprintf "WARNING: Makefile '%s' has a %s build dependency on '%s/%s' but '%s' does not implement a '%s' build type\n",
+							$pkg->{makefile}, $type, $pkg_dep->{src}, $deptype, $pkg_dep->{makefile}, $deptype;
+						next;
+					}
 					$idx = $pkg_dep->{subdir}.$pkg_dep->{src};
 				} elsif (defined($srcpackage{$dep})) {
 					$idx = $subdir{$dep}.$dep;
@@ -499,14 +506,16 @@ sub gen_package_mk() {
 			my $condition;
 			my $prefix = "";
 			my $suffix = "";
+			my $deptype = "";
 
 			if ($deps =~ /^(.+):(.+)/) {
 				$condition = $1;
 				$deps = $2;
 			}
-			if ($deps =~ /^(.+)(\/.+)/) {
+			if ($deps =~ /^(.+)\/(.+)/) {
 				$deps = $1;
-				$suffix = $2;
+				$deptype = $2;
+				$suffix = "/$2";
 			}
 
 			my $pkg_dep = $package{$deps};
@@ -521,7 +530,17 @@ sub gen_package_mk() {
 			foreach my $dep (@deps) {
 				$pkg_dep = $package{$deps};
 				if (defined $pkg_dep->{src}) {
-					($pkg->{src} ne $pkg_dep->{src}.$suffix) and $idx = $pkg_dep->{subdir}.$pkg_dep->{src};
+					unless (!$deptype || grep { $_ eq $deptype } @{$pkg_dep->{buildtypes}}) {
+						warn sprintf "WARNING: Makefile '%s' has a build dependency on '%s/%s' but '%s' does not implement a '%s' build type\n",
+							$pkg->{makefile}, $pkg_dep->{src}, $deptype, $pkg_dep->{makefile}, $deptype;
+						next;
+					}
+					unless ($pkg->{src} ne $pkg_dep->{sec}.$suffix) {
+						warn sprintf "WARNING: Makefile '%s' has a build dependency on itself\n",
+							$pkg->{makefile};
+						next;
+					}
+					$idx = $pkg_dep->{subdir}.$pkg_dep->{src};
 				} elsif (defined($srcpackage{$dep})) {
 					$idx = $subdir{$dep}.$dep;
 				}