Hi, I am using Autoconf 2.69 on Fedora Linux. Let us consider an trivial example:
$ cat configure.ac AC_INIT([foo],[0.001]) AS_IF([true],[ # Comment ]) $ autoreconf -i . $ ./configure $ cat ./configure | tail -n 10 ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5' ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5' ac_compiler_gnu=$ac_cv_c_compiler_gnu if true; then : # Comment fi Everything is ok. If the second argument of AS_IF does not include any executable commands, it is perfectly acceptable and generates valid code because AS_IF uses : command immediatelly after "then" keyword. Let us add the third argument to AS_IF: $ cat configure.ac AC_INIT([foo],[0.001]) AS_IF([true],[ # Comment ],[ # Another comment ]) $ autoreconf -i . $ ./configure ./configure: line 1670: syntax error near unexpected token `fi' ./configure: line 1670: `fi' $ cat ./configure | tail -n 10 if true; then : # Comment else # Another comment fi You see, generated code is not correct: there is no command in "else" part, bash does not like it. It is not a big problem, but it is quite confusing for newbie user. And it seems it can be easily avoided by generating ":" command in the "else" part, like AS_IF does it in "then" part of conditional statement.
