[PATCH] m4sh: allow trailing newlines in shell conditions

[Eric Blake]

Dimitrios Apostolou reported confusion in understanding why
his configure.ac was generating a shell syntax error with:

AM_CONDITIONAL([HAVE_LIBXML2],
    [test "x$with_libxml2" != xno &&
     test "x$ac_cv_lib_xml2_xmlFirstElementChild" = xyes]
)

Root cause was that his trailing newline, coupled with a
'if $2; then' construct in the macro body, resulted in
configure containing:
if test ... xyes
; then
where the semicolon is a syntax error in shell.

While that macro is not under our control, it does highlight
the fact that the shell can use either ; or newline to
terminate a conditional prior to the next keyword in a compound
statement.  If we use newline, we gain two benefits - the
configure file is slightly smaller (more lines, but fewer
bytes), and any user that doesn't realize that unquoted
trailing newlines in a macro argument are still significant
can still generate valid shell code when their argument is
used in a shell compound statement.

* lib/m4sugar/m4sh.m4 (AS_IF, _AS_IF, _AS_CLEAN_DIR): Prefer
newline over semicolon to end user-supplied conditionals.
* lib/autoconf/general.m4 (AC_CONFIG_AUX_DIRS): Likewise.
* lib/autoconf/libs.m4 (AC_SEARCH_LIBS): Likewise.
* lib/autoconf/programs.m4 (_AC_PATH_PROGS_FEATURE_CHECK):
Likewise.
* tests/m4sh.at (AS_IF and AS_CASE): Test it.

Signed-off-by: Eric Blake <address@hidden>
---
 lib/autoconf/general.m4  |  3 ++-
 lib/autoconf/libs.m4     |  3 ++-
 lib/autoconf/programs.m4 |  3 ++-
 lib/m4sugar/m4sh.m4      | 15 ++++++++++-----
 tests/m4sh.at            |  4 ++++
 5 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
index 696a9a1..59d204f 100644
--- a/lib/autoconf/general.m4
+++ b/lib/autoconf/general.m4
@@ -1700,7 +1700,8 @@ AC_DEFUN([AC_CONFIG_AUX_DIR_DEFAULT],
 # do not automatically need to distribute the other auxiliary files.
 AC_DEFUN([AC_CONFIG_AUX_DIRS],
 [ac_aux_dir=
-for ac_dir in $1; do
+for ac_dir in $1
+do
   if test -f "$ac_dir/install-sh"; then
     ac_aux_dir=$ac_dir
     ac_install_sh="$ac_aux_dir/install-sh -c"
diff --git a/lib/autoconf/libs.m4 b/lib/autoconf/libs.m4
index 50143d3..55e9468 100644
--- a/lib/autoconf/libs.m4
+++ b/lib/autoconf/libs.m4
@@ -49,7 +49,8 @@ AC_DEFUN([AC_SEARCH_LIBS],
 AC_CACHE_CHECK([for library containing $1], [ac_Search],
 [ac_func_search_save_LIBS=$LIBS
 AC_LANG_CONFTEST([AC_LANG_CALL([], [$1])])
-for ac_lib in '' $2; do
+for ac_lib in '' $2
+do
   if test -z "$ac_lib"; then
     ac_res="none required"
   else
diff --git a/lib/autoconf/programs.m4 b/lib/autoconf/programs.m4
index cdd86ea..32f737a 100644
--- a/lib/autoconf/programs.m4
+++ b/lib/autoconf/programs.m4
@@ -421,7 +421,8 @@ m4_define([_AC_PATH_PROGS_FEATURE_CHECK],
   ac_path_$1_found=false
   # Loop through the user's path and test for each of PROGNAME-LIST
   _AS_PATH_WALK([$5],
-  [for ac_prog in $2; do
+  [for ac_prog in $2
+   do
     for ac_exec_ext in '' $ac_executable_extensions; do
       ac_path_$1="$as_dir$ac_prog$ac_exec_ext"
       AS_EXECUTABLE_P(["$ac_path_$1"]) || continue
diff --git a/lib/m4sugar/m4sh.m4 b/lib/m4sugar/m4sh.m4
index 91cdeac..a94999e 100644
--- a/lib/m4sugar/m4sh.m4
+++ b/lib/m4sugar/m4sh.m4
@@ -618,9 +618,11 @@ done[]_m4_popdef([$1])])
 # AS_IF(TEST1, [IF-TRUE1 = :]...[IF-FALSE = :])
 # ---------------------------------------------
 # Expand into
-# | if TEST1; then
+# | if TEST1
+# | then
 # |   IF-TRUE1
-# | elif TEST2; then
+# | elif TEST2
+# | then
 # |   IF-TRUE2
 # [...]
 # | else
@@ -629,7 +631,8 @@ done[]_m4_popdef([$1])])
 # with simplifications when IF-TRUE1 and/or IF-FALSE are empty.
 #
 m4_define([_AS_IF],
-[elif $1; then :
+[elif $1
+then :
   $2
 ])
 m4_define([_AS_IF_ELSE],
@@ -639,7 +642,8 @@ m4_define([_AS_IF_ELSE],
 ])])

 m4_defun([AS_IF],
-[if $1; then :
+[if $1
+then :
   $2
 m4_map_args_pair([_$0], [_$0_ELSE], m4_shift2($@))]dnl
 [fi[]])# AS_IF
@@ -1389,7 +1393,8 @@ _ASBOX])
 # Remove all contents from within DIR, including any unwritable
 # subdirectories, but leave DIR itself untouched.
 m4_define([_AS_CLEAN_DIR],
-[if test -d $1; then
+[if test -d $1
+then
   find $1 -type d ! -perm -700 -exec chmod u+rwx {} \;
   rm -fr $1/* $1/.[[!.]] $1/.??*
 fi])
diff --git a/tests/m4sh.at b/tests/m4sh.at
index 5d3b194..5893389 100644
--- a/tests/m4sh.at
+++ b/tests/m4sh.at
@@ -1244,6 +1244,9 @@ AS_IF([false], [:], [ ]) && AS_CASE([foo], [foo], []
 ) && echo seventeen
 m4_define([empty])AS_IF([:], [empty]
 ) && AS_CASE([foo], [foo], [empty]) && echo eighteen
+dnl Allow for users that don't know to avoid trailing whitespace
+AS_IF([:
+], [echo nineteen])
 dnl We can't handle AS_IF([false], [:], [empty]) unless m4_expand is
 dnl taught how to handle m4_require.  The user is responsible for
 dnl avoiding the syntax error in that case.
@@ -1301,6 +1304,7 @@ fifteen
 sixteen
 seventeen
 eighteen
+nineteen
 foo1=1 bar1=1
 foo2=2 bar2=
 foo3=3 bar3=
-- 
1.9.3