Merge remote-tracking branch 'r-autothing/v3/master'

1 files changed, 23 insertions, 0 deletions

diff --git a/build-aux/Makefile.once.head/10-write-ifchanged.mk b/build-aux/Makefile.once.head/10-write-ifchanged.mk
new file mode 100644
index 0000000..649aab9
--- /dev/null
+++ b/build-aux/Makefile.once.head/10-write-ifchanged.mk
@@ -0,0 +1,23 @@
+mod.write-ifchanged.description = `write-ifchanged` auxiliary build script
+mod.write-ifchanged.files += $(topsrcdir)/build-aux/write-ifchanged
+define mod.write-ifchanged.doc
+# User variables:
+#   - `WRITE_IFCHANGED ?= $(topsrcdir)/build-aux/write-ifchanged`
+# Inputs:
+#   (none)
+# Outputs:
+#   (none)
+#
+# The $(WRITE_IFCHANGED) program reads a file from stdin, and writes it to the
+# file named in argv[1], but does so atomically, but more importantly, does so
+# in a way that does not bump the file's ctime if the new content is the same
+# as the old content.
+#
+# That is, the following lines are almost equivalient:
+#
+#     ... > $@
+#     ... | $(WRITE_ATOMIC) $@
+endef
+mod.write-ifchanged.doc := $(value mod.write-ifchanged.doc)
+
+WRITE_IFCHANGED ?= $(topsrcdir)/build-aux/write-ifchanged