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.
Pádraig Brady suggested to parse the output of tail -n1.

diff --git a/.x-sc_prohibit_empty_lines_at_EOF b/.x-sc_prohibit_empty_lines_at_EOF
new file mode 100644 (file)
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 (file)
--- 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..dfc3b86 100644 (file)
--- a/cfg.mk
+++ b/cfg.mk
@@ -315,6 +315,30 @@ sc_space_before_open_paren:
        else :;                                                         \
        fi
 
+# The following tail+perl pipeline would be much more concise, and would
+# produce slightly better output (including counts) if written as
+#   perl -ln -0777 -e '/\n(\n+)$/ and print "$ARGV: ".length $1' ...
+# but that would be far less efficient, reading the entire contents
+# of each file, rather than just the last few bytes of each.
+#
+# This is a perl script that operates on the output of
+# tail -n1 TWO_OR_MORE_FILES
+# Print the name of each file that ends in two or more newline bytes.
+# Exit nonzero if at least one such file is found, otherwise, exit 0.
+#
+# Use this if you want to remove trailing empty lines from selected files:
+#   perl -pi -0777 -e 's/\n\n+$/\n/' files...
+#
+detect_empty_lines_at_EOF_ =                                           \
+  /^==> ([^\n]+) <==\n\n/m and (print "$$1\n"), $$fail = 1;            \
+  END { exit defined $$fail }
+
+sc_prohibit_empty_lines_at_EOF:
+       @tail -n1 $$($(VC_LIST_EXCEPT)) /dev/null                       \
+           | perl -00 -ne '$(detect_empty_lines_at_EOF_)'              \
+         || { echo '$(ME): the above files end with empty line(s)'     \
+               1>&2; exit 1; } || :;                                   \
+
 include $(srcdir)/dist-check.mk
 
 update-copyright-env = \