From 621523db6238fff5362aded06abc6c9e78170a22 Mon Sep 17 00:00:00 2001
From: David Given <dg@cowlark.com>
Date: Sun, 31 Mar 2024 21:30:26 +0200
Subject: [PATCH] Try not to build fallback packages unless necessary.

---
 build/pkg.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/build/pkg.py b/build/pkg.py
index f7677bca..8b41a9f4 100644
--- a/build/pkg.py
+++ b/build/pkg.py
@@ -16,9 +16,6 @@ HOST_PACKAGES := $(shell $(HOST_PKG_CONFIG) --list-all | cut -d' ' -f1 | sort)
 
 @Rule
 def package(self, name, package=None, fallback: Target = None):
-    self.ins = []
-    self.outs = []
-
     emit("ifeq ($(filter %s, $(PACKAGES)),)" % package)
     if fallback:
         emit(
@@ -29,7 +26,7 @@ def package(self, name, package=None, fallback: Target = None):
             f"PACKAGE_LDFLAGS_{package} := ",
             bubbledattrsof(fallback, "caller_ldflags"),
         )
-        self.outs = filenamesof(fallback)
+        emit(f"PACKAGE_DEPS_{package} := ", filenamesof(fallback))
     else:
         emit(f"$(error Required package '{package}' not installed.)")
     emit("else")
@@ -39,6 +36,7 @@ def package(self, name, package=None, fallback: Target = None):
     emit(
         f"PACKAGE_LDFLAGS_{package} := $(shell $(PKG_CONFIG) --libs {package})"
     )
+    emit(f"PACKAGE_DEPS_{package} :=")
     emit("endif")
 
     self.attr.caller_cflags = [f"$(PACKAGE_CFLAGS_{package})"]
@@ -46,6 +44,9 @@ def package(self, name, package=None, fallback: Target = None):
     self.traits.add("clibrary")
     self.traits.add("cheaders")
 
+    self.ins = []
+    self.outs = [f"$(PACKAGE_DEPS_{package})"]
+
 
 @Rule
 def hostpackage(self, name, package=None, fallback: Target = None):