Use diff to get better dates

See the comments for more information, including Macintosh quirks. This
is a great deal better than using `ls` and allows for the dropping of
the latter as a dependency.

diff --git a/GNUmakefile b/GNUmakefile
index 2c77723f6fd24507cd0c9b8331a3648212fb0524..6779aa72cf85f91c978bae7db2bd89aa9b13f5a2 100644 (file)
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -22,12 +22,12 @@ override define makefileinfo
 ║│ • cksum                                                    │║
 ║│ • cp                                                       │║
 ║│ • date                                                     │║
+║│ • diff                                                     │║
 ║│ • file                                                     │║
 ║│ • find                                                     │║
 ║│ • grep                                                     │║
 ║│ • git (optional)                                           │║
 ║│ • ln                                                       │║
-║│ • ls                                                       │║
 ║│ • mkdir                                                    │║
 ║│ • mv                                                       │║
 ║│ • od                                                       │║
@@ -102,12 +102,12 @@ CAT := cat
 CKSUM := cksum
 CP := cp
 DATE := date
+DIFF := diff
 FILE := file
 FIND := find
 GIT := git
 GREP := grep
 LN := ln
-LS := ls
 MKDIR := mkdir
 MV := mv
 OD := od
@@ -255,17 +255,13 @@ override quote = '$(subst ','"'"',$1)'
 
 # (callable) Get the modified time of the provided file.
 #
-# Only the date·time information available via `ls -l´ is supported; that is, only minute precision for files newer than six months, and only day precision for files which are older.
-# This is, unfortunately, the best that can be done in pure Posix as of now.
+# This touches a file containing only a newline and then diffs it with `/dev/null´ and extracts the timestamp from the diff.
+# Interestingly, on Macintosh, the format of `diff -u´ is only Posixy (including a fractional component and timezone) when `COMMAND_MODE=legacy´; however, the timezone will always be zero and the fractional component is ignorable, so it’s not necessary to worry about that here.
 #
-# There is an easier implementation which provides the full date·time by archiving an empty file and then reading it back out of the archive :—
-#
-#     $(shell LC_TIME=POSIX TZ=UTC0 $(TOUCH) -m -r $(callquote,$1) $(BUILDDIR)/.mtime && $(PAX) -w -x ustar $(BUILDDIR)/.mtime | $(PAX) -v -o 'listopt=%(mtime=%Y-%m-%dT%H:%M:%SZ)T')
-#
-# However, it depends on the `listopt´ option in `pax´, which (despite being specified in Posix) no implementations actually support.
+# The diff will always have an exit status of 1, but this is ignored by piping into Sed.
 #
 # ☡ This variable creates a subshell every time it is computed.
-override modtime = $(shell { $(DATE) -u '+%Y-%m'; LC_TIME=POSIX TZ=UTC0 ls -q -A -l $(call quote,$1) | $(SED) 's/\([^ ]* \{1,\}\)\{5\}\(\([^ ]* \{1,\}\)\{3\}\).*/\2/;s/ \([0123456789]\) / 0\1 /;s/Jan/01/;s/Feb/02/;s/Mar/03/;s/Apr/04/;s/May/05/;s/Jun/06/;s/Jul/07/;s/Aug/08/;s/Sep/09/;s/Oct/10/;s/Nov/11/;s/Dec/12/;s/\([0123456789]\{2\}\) *\([0123456789]\{2\}\) *\([0123456789]\{4\}\)/\3-\1-\2T00:00:00Z/;s/\([0123456789]\{2\}\) *\([0123456789]\{2\}\) *\([0123456789:]\{5\}\)/XXXX-\1-\2T\3:00Z/'; } | $(TR) -d ' ' | $(AWK) -F '-' 'NR==1{year=$$1;month=$$2}$$1=="XXXX"&&$$2<=month{print year"-"$$2"-"$$3}$$1=="XXXX"&&$$2>month{print year-1"-"$$2"-"$$3}NR>1&&$$1!="XXXX"')
+override modtime = $(shell if $(TEST) ! -f $(call quote,$(BUILDDIR)/.mtime); then $(PRINTF) '%b' '\n' > $(call quote,$(BUILDDIR)/.mtime); fi; $(TOUCH) -r $(call quote,$1) $(call quote,$(BUILDDIR)/.mtime); TZ=UTC0 $(DIFF) -u $(call quote,$(BUILDDIR)/.mtime) /dev/null | $(SED) '1!d;s/.*  \([^ ]*\) \([^ ]*\).*$$/\1T\2Z/')
 
 # ─ ¶ Recipe Variable Definitions ─────────────────────────────────────
 

diff --git a/README.markdown b/README.markdown
index 3375b8a36eb7b7bcdc63e078d6676da0c71f7708..8a6efb8afdd623b1f62fd39f1eb543b483dc4985 100644 (file)
--- a/README.markdown
+++ b/README.markdown
@@ -184,12 +184,12 @@ In every case, you may supply your own implementation by overriding the
 - `cksum`
 - `cp`
 - `date`
+- `diff`
 - `file`
 - `find`
 - `git` (optional; set `GIT=` to disable)
 - `grep`
 - `ln`
-- `ls`
 - `mkdir`
 - `mv`
 - `od`
@@ -571,10 +571,6 @@ The following params are made available globally in parsers and
 
 - **`SRCTIME`:**
   The time at which the source file was last modified.
-  Due to limitations in Posix, this time will only have minute
-    precision if the file was modified in the last six months, and will
-    only have day precision if the file is older.
-  Users should not expect this value to be particularly stable.
 
 - **`THISREV`:**
   The value of the `THISREV` variable (if present).