From 1d52d5c5372a43655a252880d34088fa56aa2530 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dag-Erling=20Sm=C3=B8rgrav?= <des@FreeBSD.org>
Date: Wed, 31 Dec 2025 14:10:20 +0100
Subject: [PATCH] depend-cleanup: Force a clean build when options change

Similar to the build epoch check, cache a list of source options in the
object tree, and force a clean build if the cached list does not match
the current list, after filtering out options which are known not to
affect the build (e.g. CLEAN, TESTS, WARNS).

This also adds a DEPEND_CLEANUP option (which defaults to yes unless
the CLEAN option is set) which can be used to skip depend-cleanup for
faster incremental builds.

MFC after:	1 week
Reviewed by:	imp
Differential Revision:	https://reviews.freebsd.org/D52011
---
 Makefile.inc1                              |  6 ++-
 share/man/man5/src.conf.5                  | 14 +++++
 share/mk/src.opts.mk                       |  5 ++
 tools/build/depend-cleanup.sh              | 61 ++++++++++++++++++----
 tools/build/options/WITHOUT_DEPEND_CLEANUP |  5 ++
 5 files changed, 79 insertions(+), 12 deletions(-)
 create mode 100644 tools/build/options/WITHOUT_DEPEND_CLEANUP

diff --git a/Makefile.inc1 b/Makefile.inc1
index c0bf42c3d00..8966f96de9b 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -1071,10 +1071,12 @@ _sanity_check: .PHONY .MAKE
 # tree changes, particularly with respect to removing source files and
 # replacing generated files.  Handle these cases here in an ad-hoc fashion.
 _cleanobj_fast_depend_hack: .PHONY
+.if ${MK_DEPEND_CLEANUP} != "no"
 	@echo ">>> Deleting stale dependencies...";
 	MACHINE=${MACHINE} MACHINE_ARCH=${MACHINE_ARCH} \
-	    ALL_libcompats=${_ALL_libcompats:Q} \
+	    ALL_libcompats=${_ALL_libcompats:Q} MAKE=${MAKE} \
 	    sh ${.CURDIR}/tools/build/depend-cleanup.sh ${OBJTOP} ${SRCTOP}
+.endif
 
 _cleanworldtmp: .PHONY
 .if ${MK_CLEAN} == "yes"
@@ -1168,7 +1170,7 @@ _cleanobj:
 .endfor
 .else
 	${_+_}cd ${.CURDIR}; env CLEANMK="_NO_INCLUDE_COMPILERMK=t ${CLEANDIR}" \
-	    MAKE=${MAKE} ${WMAKE} _cleanobj_fast_depend_hack
+	    ${WMAKE} _cleanobj_fast_depend_hack
 .endif	# ${MK_CLEAN} == "yes"
 _obj:
 	@echo
diff --git a/share/man/man5/src.conf.5 b/share/man/man5/src.conf.5
index f028a3d1aac..eaed8f9e3fb 100644
--- a/share/man/man5/src.conf.5
+++ b/share/man/man5/src.conf.5
@@ -449,6 +449,14 @@ Clean before building world and/or kernel.
 Note that recording a new epoch in
 .Pa .clean_build_epoch
 in the root of the source tree will also force a clean world build.
+When set, these options are also in effect:
+.Pp
+.Bl -inset -compact
+.It Va WITHOUT_DEPEND_CLEANUP
+(unless
+.Va WITH_DEPEND_CLEANUP
+is set explicitly)
+.El
 .It Va WITHOUT_CPP
 Do not build
 .Xr cpp 1 .
@@ -537,6 +545,12 @@ amd64/amd64, arm64/aarch64, i386/i386, powerpc/powerpc64 and powerpc/powerpc64le
 .It Va WITHOUT_DEBUG_FILES
 Avoid building or installing standalone debug files for each
 executable binary and shared library.
+.It Va WITHOUT_DEPEND_CLEANUP
+Do not attempt to detect if the object tree needs cleaning in part or in
+whole before building.
+This speeds up incremental builds, especially when experimenting with
+build options, but may cause the build to inexplicably fail or produce
+non-functioning binaries.
 .It Va WITH_DETECT_TZ_CHANGES
 Make the time handling code detect changes to the timezone files.
 .It Va WITH_DIALOG
diff --git a/share/mk/src.opts.mk b/share/mk/src.opts.mk
index 0d806702417..68d48271d7b 100644
--- a/share/mk/src.opts.mk
+++ b/share/mk/src.opts.mk
@@ -86,6 +86,7 @@ __DEFAULT_YES_OPTIONS = \
     CRYPT \
     CUSE \
     CXGBETOOL \
+    DEPEND_CLEANUP \
     DICT \
     DMAGENT \
     DTRACE \
@@ -515,6 +516,10 @@ MK_LLVM_CXXFILT:=	yes
 MK_LOADER_VERIEXEC_PASS_MANIFEST := no
 .endif
 
+.if ${MK_CLEAN} == "yes"
+MK_DEPEND_CLEANUP:=	no
+.endif
+
 #
 # MK_* options whose default value depends on another option.
 #
diff --git a/tools/build/depend-cleanup.sh b/tools/build/depend-cleanup.sh
index f5d2fdac9df..ff7d4b2a592 100755
--- a/tools/build/depend-cleanup.sh
+++ b/tools/build/depend-cleanup.sh
@@ -124,10 +124,8 @@ if [ ! -d "$SRCTOP" -o ! -f "$SRCTOP/Makefile.inc1" ]; then
 fi
 
 : ${CLEANMK=""}
-if [ -n "$CLEANMK" ]; then
-	if [ -z "${MAKE+set}" ]; then
-		err "MAKE not set"
-	fi
+if [ -z "${MAKE+set}" ]; then
+	err "MAKE not set"
 fi
 
 if [ -z "${MACHINE+set}" ]; then
@@ -202,9 +200,41 @@ extract_epoch()
 	awk 'int($1) > 0 { epoch = $1 } END { print epoch }' "$1"
 }
 
+# Regular expression matching the names of src.conf(5) options which
+# don't affect the build.
+#
+# This filter is applied to both the current options and the cached
+# options so we don't force a rebuild just because the filter itself
+# changed.
+IGNORED_OPTS="CLEAN|DEPEND_CLEANUP|EXAMPLES|MAN|TESTS|WARNS|WERROR"
+IGNORED_OPTS="${IGNORED_OPTS}|INSTALL.*|STAGING.*"
+# Also ignore TOOLCHAIN and the options it forces if set.  It is
+# commonly used to speed up a build and is safe to toggle.
+IGNORED_OPTS="${IGNORED_OPTS}|TOOLCHAIN|CLANG.*|LLDB?|LLVM_(BIN|COV).*"
+
+extract_src_opts()
+{
+	$MAKE -C "$SRCTOP" -f "$SRCTOP"/Makefile.inc1 \
+	    -V $'SRC_OPT_LIST:O:ts\n' |
+	egrep -v "^WITH(OUT)?_(${IGNORED_OPTS})="
+}
+
+extract_obj_opts()
+{
+	for fn; do
+		if [ -f "${fn}" ]; then
+			cat "${fn}"
+		else
+			echo "# ${fn}"
+		fi
+	done |
+	egrep -v "^WITH(OUT)?_(${IGNORED_OPTS})="
+}
+
 clean_world()
 {
 	local buildepoch="$1"
+	local srcopts="$2"
 
 	# The caller may set CLEANMK in the environment to make target(s) that
 	# should be invoked instead of just destroying everything.  This is
@@ -227,34 +257,45 @@ clean_world()
 
 	mkdir -p "$OBJTOP"
 	echo "$buildepoch" > "$OBJTOP"/.clean_build_epoch
+	echo "$srcopts" > "$OBJTOP"/.src_opts
 
 	exit 0
 }
 
-check_epoch()
+check_epoch_and_opts()
 {
 	local srcepoch objepoch
+	local srcopts objopts
 
 	srcepoch=$(extract_epoch "$SRCTOP"/.clean_build_epoch)
 	if [ -z "$srcepoch" ]; then
 		err "Malformed .clean_build_epoch; please validate the last line"
 	fi
 
+	srcopts=$(extract_src_opts)
+	if [ -z "$srcopts" ]; then
+		err "Unable to extract source options"
+	fi
+
 	# We don't discriminate between the varying degrees of difference
 	# between epochs.  If it went backwards we could be bisecting across
 	# epochs, in which case the original need to clean likely still stands.
 	objepoch=$(extract_epoch "$OBJTOP"/.clean_build_epoch)
 	if [ -z "$objepoch" ] || [ "$srcepoch" -ne "$objepoch" ]; then
-		if [ "$VERBOSE" ]; then
-			echo "Cleaning - src epoch: $srcepoch, objdir epoch: ${objepoch:-unknown}"
-		fi
+		echo "Cleaning - src epoch: $srcepoch, objdir epoch: ${objepoch:-unknown}"
+		clean_world "$srcepoch" "$srcopts"
+		# NORETURN
+	fi
 
-		clean_world "$srcepoch"
+	objopts=$(extract_obj_opts "$OBJTOP"/.src_opts)
+	if [ "$srcopts" != "$objopts" ]; then
+		echo "Cleaning - build options have changed"
+		clean_world "$srcepoch" "$srcopts"
 		# NORETURN
 	fi
 }
 
-check_epoch
+check_epoch_and_opts
 
 #### Typical dependency cleanup begins here.
 
diff --git a/tools/build/options/WITHOUT_DEPEND_CLEANUP b/tools/build/options/WITHOUT_DEPEND_CLEANUP
new file mode 100644
index 00000000000..6972ece98be
--- /dev/null
+++ b/tools/build/options/WITHOUT_DEPEND_CLEANUP
@@ -0,0 +1,5 @@
+Do not attempt to detect if the object tree needs cleaning in part or in
+whole before building.
+This speeds up incremental builds, especially when experimenting with
+build options, but may cause the build to inexplicably fail or produce
+non-functioning binaries.