[PATCH] maint: new syntax-check rule: prohibit empty lines at EOF

[Jim Meyering]

Here's a rule I'm adding to coreutils' cfg.mk.
However, I would like to use it several other projects,
so rather than duplicating it in each, I'm thinking of
putting it in gnulib's maint.mk.

Opinions?

I know that at least Bruno likes to retain trailing empty
lines in modules/ files.  But for a class of files like that,
it's easy to exempt "^modules/" or to omit the rule altogether.

Does anyone object to my adding this syntax check to maint.mk?

Aside from that, can anyone improve on the code?
The multi-line Perl script is the only way I could get
the efficiency I wanted, but there may well be another
more concise way.

>From bc6da1230dfc7c998deefab9cb1890907b6da595 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Sat, 10 Apr 2010 14:19:11 +0200
Subject: [PATCH] maint: new syntax-check rule: prohibit empty lines at EOF

* cfg.mk (detect_empty_lines_at_EOF_): Define.
(sc_prohibit_empty_lines_at_EOF): New rule.
* .x-sc_prohibit_empty_lines_at_EOF: New file.  Exempt pr test inputs.
* Makefile.am (syntax_check_exceptions): Add it.
---
 .x-sc_prohibit_empty_lines_at_EOF |    1 +
 Makefile.am                       |    1 +
 cfg.mk                            |   34 ++++++++++++++++++++++++++++++++++
 3 files changed, 36 insertions(+), 0 deletions(-)
 create mode 100644 .x-sc_prohibit_empty_lines_at_EOF

diff --git a/.x-sc_prohibit_empty_lines_at_EOF 
b/.x-sc_prohibit_empty_lines_at_EOF
new file mode 100644
index 0000000..92571d6
--- /dev/null
+++ b/.x-sc_prohibit_empty_lines_at_EOF
@@ -0,0 +1 @@
+^tests/pr/
diff --git a/Makefile.am b/Makefile.am
index 1eb9c12..9a7f45c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -47,6 +47,7 @@ syntax_check_exceptions =             \
   .x-sc_po_check                       \
   .x-sc_program_name                   \
   .x-sc_prohibit_atoi_atof             \
+  .x-sc_prohibit_empty_lines_at_EOF    \
   .x-sc_prohibit_fail_0                        \
   .x-sc_prohibit_magic_number_exit     \
   .x-sc_prohibit_stat_st_blocks                \
diff --git a/cfg.mk b/cfg.mk
index 75ce77a..75f4be0 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -315,6 +315,40 @@ sc_space_before_open_paren:
        else :;                                                         \
        fi

+# This Perl code is slightly obfuscated.  Not only is each "$" doubled
+# because it's in a Makefile, but the $$c's are comments;  we cannot
+# use "#" due to the way the script ends up concatentated onto one line.
+# It would be much more concise, and with better output (including counts) as
+#   perl -ln -0777 -e '/\n(\n+)$/ and print "$ARGV: ".length $1' ...
+# but that would be far less efficient, reading the entire contents
+# of each file, rather than just the last two bytes of each.
+#
+# This is a perl script that is expected to be the single-quoted argument
+# to a command-line "-le".  The remaining arguments are file names.
+# Print the name of each file that ends in two or more newline bytes.
+# Exit nonzero if at least one such file is found, otherwise, exit 0.
+# Warn about, but otherwise ignore open failure.  Ignore seek/read failure.
+#
+# Use this if you want to remove trailing empty lines from selected files:
+#   perl -pi -0777 -e 's/\n\n+$/\n/' ...
+#
+detect_empty_lines_at_EOF_ =                                           \
+  foreach my $$f (@ARGV) {                                             \
+    open F, "<", $$f or (warn "failed to open $$f: $$!\n"), next;      \
+    my $$p = sysseek (F, -2, 2);                                       \
+    my $$c = "seek failure probably means file has < 2 bytes; ignore"; \
+    my $$two;                                                          \
+    defined $$p and $$p = sysread F, $$two, 2;                         \
+    close F;                                                           \
+    $$c = "ignore read failure";                                       \
+    $$p && $$two eq "\n\n" and (print $$f), $$fail=1;                  \
+    } END { exit defined $$fail }
+
+sc_prohibit_empty_lines_at_EOF:
+       @perl -le '$(detect_empty_lines_at_EOF_)' $$($(VC_LIST_EXCEPT)) \
+         || { echo '$(ME): the above files have empty lines at EOF'    \
+               1>&2; exit 1; } || :;                                   \
+
 include $(srcdir)/dist-check.mk

 update-copyright-env = \
--
1.7.1.rc0.264.g94f6e