Documentation for clean.sd.mk and cdeps.sd.mk

[subdirmk.git] / subdirmk / cdeps.sd.mk

diff --git a/subdirmk/cdeps.sd.mk b/subdirmk/cdeps.sd.mk
index aeb35bf88427385246cf02a841b544325f22d9c1..402e687c6aa63153951e95e704d02f488a77d547 100644 (file)
--- a/subdirmk/cdeps.sd.mk
+++ b/subdirmk/cdeps.sd.mk
@@ -1,5 +1,24 @@
+# subdirmk - useful rules for making and using cpp .*.d files
+#  Copyright 2019 Mark Wooding
+#  Copyright 2019 Ian Jackson
+# SPDX-License-Identifier: LGPL-2.0-or-later
+
+&# Usage:
+&#   &:include subdirmk/cdeps.sd.mk
+&# (probably in Perdir.sd.mk)
+&#
+&# Arranges for automatic #include dependency tracking for
+&# C compilation.  The compiler is asked to write the dependencies to
+&#  .*.d and these are automatically included.
+&#
+&# There is a bug: if a #included file is deleted and all references
+&# in .c files to it removed, `make' will complain that it is needed
+&# and can't be built.  `make clean' will fix this.
+
+CDEPS_CFLAGS ?= -MD -MF $(*D)/.$(*F).d
 
 &DEPFILES += $(foreach b,$(patsubst %.o,%,$(&OBJECTS)), \
                $(dir $b).$(notdir $b).d)
 -include $(&DEPFILES)
 
+&CLEAN += $(&DEPFILES)