From 614824992749cc13ccbbd5e22f343746bdb0a12a Mon Sep 17 00:00:00 2001
From: Hojun-Cho <ghwns6743@gmail.com>
Date: Sat, 8 Aug 2026 04:09:21 +0900
Subject: [PATCH] =?UTF-8?q?make:=20test-incremental=20gate=20=E2=80=94=20-?=
 =?UTF-8?q?w=20reuse=20must=20equal=20a=20clean=20build?=
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Cold populate, full-skip rerun, surgical staleness (one package's
artifacts deleted), and a 0-byte .o poison drill each build the w6a
graph through a persistent workdir and must be byte-identical to a
classic fresh-scratch build, on both driver stages, plus the
cross-stage clean compare. Wired into test-all; the inner-loop targets
stay untaxed.
---
 Makefile | 44 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 42 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 3c2ab7ef..1a734d7f 100644
--- a/Makefile
+++ b/Makefile
@@ -605,9 +605,49 @@ test-data-byteid: $(BIN)/ww $(BIN)/w6c $(BIN)/w6c_ww
 
 test-byteid: test-lang-byteid test-data-byteid test-native-byteid
 
+# Incremental == clean. The -w reuse path must be byte-identical to a
+# from-scratch build, or it is not a build-graph optimization but a
+# correctness bug. Four warm shapes per driver stage — cold populate,
+# full-skip rerun, surgical staleness (one package's artifacts deleted),
+# and a 0-byte .o poison drill (must recompile, never reuse) — each
+# compared against a classic fresh-scratch build, plus the cross-stage
+# clean compare. The w6a graph keeps the gate small while covering the
+# skip, recompile, commit, and legal-empty-.s (FFI-only rt) paths.
+INCR_DIR = $(OUT)/incrcheck
+test-incremental: $(BIN)/ww $(BIN)/ww_ww $(BIN)/w6c $(BIN)/w6c_ww \
+		$(BIN)/w6a $(BIN)/w6a_ww $(BIN)/w6l $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a
+	@rm -rf $(INCR_DIR)
+	@set -e; \
+	src=$(CURDIR)/selfhost/cmd/w6a/main.ww; \
+	inc=$(CURDIR)/selfhost/cmd/w6a; \
+	for stage in cs ws; do \
+		drv=$(CURDIR)/$(BIN)/ww; \
+		if [ $$stage = ws ]; then drv=$(CURDIR)/$(BIN)/ww_ww; fi; \
+		w=$(INCR_DIR)/$$stage.w; mkdir -p $$w; \
+		$$drv build -w $$w -o $(INCR_DIR)/$$stage.cold -I $$inc $$src; \
+		$$drv build -w $$w -o $(INCR_DIR)/$$stage.warm -I $$inc $$src; \
+		rm $$w/strings.s $$w/strings.o $$w/strings.a; \
+		$$drv build -w $$w -o $(INCR_DIR)/$$stage.surg -I $$inc $$src; \
+		: > $$w/bytes.o; \
+		$$drv build -w $$w -o $(INCR_DIR)/$$stage.heal -I $$inc $$src; \
+		(cd $(INCR_DIR) && $$drv build -o $$stage.clean -I $$inc $$src); \
+		for v in cold warm surg heal; do \
+			cmp $(INCR_DIR)/$$stage.$$v $(INCR_DIR)/$$stage.clean || { \
+				echo "test-incremental: $$stage.$$v differs from clean" >&2; \
+				exit 1; }; \
+		done; \
+	done; \
+	cmp $(INCR_DIR)/cs.clean $(INCR_DIR)/ws.clean || { \
+		echo "test-incremental: cstage/wwstage clean builds differ" >&2; \
+		exit 1; }; \
+	rm -rf $(INCR_DIR) || { echo "test-incremental: cleanup failed" >&2; exit 1; }; \
+	echo "test-incremental: -w reuse byte-identical to clean, both stages"
+
 test-bootstrap: bootstrap test-bootstrap-native
 
-test-all: test-commit test-byteid test-bootstrap test-platform test-wwfixture
+test-all: test-commit test-byteid test-bootstrap test-platform \
+	test-wwfixture test-incremental
 
 install: all
 	mkdir -p $(PREFIX)/bin $(PREFIX)/lib
@@ -768,5 +808,5 @@ nocc:
 	test test-unit test-compiler-smoke test-compiler test-package \
 	test-lang test-library test-commit test-lang-byteid \
 	test-data-byteid test-native-byteid test-byteid \
-	test-bootstrap-native test-bootstrap \
+	test-bootstrap-native test-bootstrap test-incremental \
 	test-platform test-all install clean bootstrap nocc bootstrap-snapshot