build: introduce declarative non-recursive build graph

1 files changed, 81 insertions, 0 deletions

diff --git a/scripts/build/targets.mk b/scripts/build/targets.mk
new file mode 100644
index 0000000..1a66379
--- /dev/null
+++ b/scripts/build/targets.mk
@@ -0,0 +1,81 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) 2026 Richard Qin
+
+# Declarative target registry for the LumeOS build.
+#
+# Build.mk files populate target.<name>.* and append the name to targets.  A
+# target name is metadata, not a Make rule, so names may contain '/' and ':'.
+
+target-kinds := \
+    interface-library header-library object-library source-set \
+    static-library whole-archive host-library phys-library host-tool generated \
+    binary-blob kernel-test host-test product
+targets :=
+generated-actions := autoconf asm-offsets linker-script initramfs
+
+empty :=
+space := $(empty) $(empty)
+comma := ,
+
+# Convert a logical target/source name into a path-safe component.
+target-key = $(subst :,_,$(subst /,_,$(1)))
+
+# Recursively collect a target and all of its dependencies. Dependency cycles
+# are rejected separately before this is evaluated for build roots.
+target-deps = $(sort $(target.$(1).deps) $(target.$(1).public-deps) \
+    $(target.$(1).private-deps) $(target.$(1).interface-deps) \
+    $(target.$(1).link-deps) $(target.$(1).tool-deps) \
+    $(target.$(1).generated-deps) $(target.$(1).runtime-deps) \
+    $(target.$(1).order-only-deps))
+target-closure = $(strip \
+    $(if $(filter $(1),$(2)),$(error target dependency cycle: $(2) -> $(1))) \
+    $(1) $(foreach dep,$(call target-deps,$(1)),$(call target-closure,$(dep),$(2) $(1))))
+target-link-deps = $(sort $(target.$(1).deps) $(target.$(1).public-deps) \
+    $(target.$(1).private-deps) $(target.$(1).interface-deps) \
+    $(target.$(1).link-deps))
+target-link-order = $(strip $(1) $(foreach dep,$(call target-link-deps,$(1)),\
+    $(call target-link-order,$(dep))))
+unique-words = $(if $(strip $(1)),$(firstword $(1)) \
+    $(call unique-words,$(filter-out $(firstword $(1)),$(1))))
+
+duplicate-words = $(sort $(foreach word,$(1),\
+    $(if $(word 2,$(filter $(word),$(1))),$(word))))
+all-target-sources = $(foreach target,$(targets),$(target.$(target).sources))
+duplicate-target-sources = $(call duplicate-words,$(all-target-sources))
+
+define validate-target
+$(if $(filter $(target.$(1).kind),$(target-kinds)),,$(error target '$(1)' has invalid kind '$(target.$(1).kind)'))
+$(if $(filter header-library interface-library product generated binary-blob,$(target.$(1).kind)),$(if $(strip $(target.$(1).sources)),$(error target '$(1)' of kind $(target.$(1).kind) declares sources),),)
+$(if $(filter host-tool,$(target.$(1).kind)),$(if $(word 2,$(target.$(1).sources)),$(error host-tool '$(1)' currently requires exactly one source),),)
+$(foreach src,$(target.$(1).sources),$(if $(wildcard $(src)),,$(error target '$(1)' references missing source '$(src)')))
+$(foreach dep,$(call target-deps,$(1)),$(if $(filter $(dep),$(targets)),,$(error target '$(1)' references unknown dependency '$(dep)')))
+$(foreach dep,$(call target-deps,$(1)),$(if $(strip $(target.$(dep).visibility)),\
+    $(if $(filter all $(1),$(target.$(dep).visibility)),,\
+    $(error target '$(1)' cannot depend on '$(dep)': visibility is '$(target.$(dep).visibility)')),))
+$(if $(filter generated,$(target.$(1).kind)),$(if $(strip $(target.$(1).outputs)),,$(error generated target '$(1)' has no outputs)),)
+$(if $(filter generated,$(target.$(1).kind)),$(if $(filter $(target.$(1).action),$(generated-actions)),,$(error generated target '$(1)' has invalid action '$(target.$(1).action)')),)
+endef
+
+define validate-targets
+$(if $(strip $(targets)),,$(error no build targets were registered))
+$(if $(filter-out $(words $(sort $(targets))),$(words $(targets))),$(error duplicate build target name),)
+$(foreach target,$(targets),$(call validate-target,$(target)))
+endef
+
+# Usage requirements are deliberately separate from link inputs. Public
+# include paths and defines propagate through deps; private values apply only
+# while compiling the target itself.
+target-public-closure = $(sort $(1) $(foreach dep,$(target.$(1).public-deps) \
+    $(target.$(1).deps),$(call target-public-closure,$(dep))))
+target-public-includes = $(sort $(foreach target,$(call target-public-closure,$(1)),$(target.$(target).public-includes)))
+target-public-after-includes = $(sort $(foreach target,$(call target-public-closure,$(1)),$(target.$(target).public-after-includes)))
+target-public-defines = $(sort $(foreach target,$(call target-public-closure,$(1)),$(target.$(target).public-defines)))
+
+target-usage-roots = $(sort $(1) $(target.$(1).deps) $(target.$(1).public-deps) \
+    $(target.$(1).private-deps) $(target.$(1).interface-deps))
+target-compile-includes = $(sort $(target.$(1).private-includes) \
+    $(foreach root,$(call target-usage-roots,$(1)),$(call target-public-includes,$(root))))
+target-compile-after-includes = $(sort $(target.$(1).private-after-includes) \
+    $(foreach root,$(call target-usage-roots,$(1)),$(call target-public-after-includes,$(root))))
+target-compile-defines = $(sort $(target.$(1).private-defines) \
+    $(foreach root,$(call target-usage-roots,$(1)),$(call target-public-defines,$(root))))