configure: fix broken m4 syntax in TLS options

[cgpe-a]

Commit b589696 added lines to some shell within AC_ARG_WITH macros, but
inadvertently failed to move the final closing ). e.g.:

OPT_RUSTLS=no
AC_ARG_WITH(rustls,dnl
AS_HELP_STRING([--with-rustls=PATH],[where to look for rustls, PATH points to the installation root]),
  OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    test -z "TLSCHOICE" || TLSCHOICE="${TLSCHOICE:+$TLSCHOICE, }rustls")
    experimental="$experimental rustls"
  fi

This generates a broken looking configure script:

# Check whether --with-rustls was given.
if test "${with_rustls+set}" = set; then :
  withval=$with_rustls; OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    test -z "TLSCHOICE" || TLSCHOICE="${TLSCHOICE:+$TLSCHOICE
else
  }rustls"
fi

    experimental="$experimental rustls"
  fi

But amazingly, it executes OK, due to balancing " quotes and if/fi, as
you can see if you reformat the white space:

# Check whether --with-rustls was given.
if test "${with_rustls+set}" = set; then :
  withval=$with_rustls; OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    test -z "TLSCHOICE" || TLSCHOICE="${TLSCHOICE:+$TLSCHOICE else }rustls"
  fi

  experimental="$experimental rustls"
fi

We move the closing ) back to the end of the section of script:

OPT_RUSTLS=no
AC_ARG_WITH(rustls,dnl
AS_HELP_STRING([--with-rustls=PATH],[where to look for rustls, PATH points to the installation root]),
  OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    test -z "TLSCHOICE" || TLSCHOICE="${TLSCHOICE:+$TLSCHOICE, }rustls"
    experimental="$experimental rustls"
  fi
)

However, with this change alone the generated configure script is still broken:

# Check whether --with-rustls was given.
if test "${with_rustls+set}" = set; then :
  withval=$with_rustls; OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    test -z "TLSCHOICE" || TLSCHOICE="${TLSCHOICE:+$TLSCHOICE
else
  }rustls"
    experimental="$experimental rustls"
  fi

fi

This is because there is an unquoted comma in the script,
unintentionally separating AC_ARG_WITH arguments. We need to quote the
script section using braces:

OPT_RUSTLS=no
AC_ARG_WITH(rustls,dnl
AS_HELP_STRING([--with-rustls=PATH],[where to look for rustls, PATH points to the installation root]),[
  OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    test -z "TLSCHOICE" || TLSCHOICE="${TLSCHOICE:+$TLSCHOICE, }rustls"
    experimental="$experimental rustls"
  fi
])

The generated script now has sane shell syntax:

# Check whether --with-rustls was given.
if test "${with_rustls+set}" = set; then :
  withval=$with_rustls;
  OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    test -z "TLSCHOICE" || TLSCHOICE="${TLSCHOICE:+$TLSCHOICE, }rustls"
    experimental="$experimental rustls"
  fi

fi

However, the 'test -z "TLSCHOICE" ||' part is a no-op, the same as
'false ||'. Perhaps it was cut-and-pasted from somewhere else, and a
dollar before TLSCHOICE was accidentaly deleted. However, with that
change, TLSCHOICE would never be set.

The code on the rhs of the || makes sense - it appends the new value,
separating it from any previous value with ", ". So, we can simplify by
removing the no-op test. This gives us:

OPT_RUSTLS=no
AC_ARG_WITH(rustls,dnl
AS_HELP_STRING([--with-rustls=PATH],[where to look for rustls, PATH points to the installation root]),[
  OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    TLSCHOICE="${TLSCHOICE:+$TLSCHOICE, }rustls"
    experimental="$experimental rustls"
  fi
])

Generating:

# Check whether --with-rustls was given.
if test "${with_rustls+set}" = set; then :
  withval=$with_rustls;
  OPT_RUSTLS=$withval
  if test X"$withval" != Xno; then
    TLSCHOICE="${TLSCHOICE:+$TLSCHOICE, }rustls"
    experimental="$experimental rustls"
  fi

fi

As far as I can tell, the quoting problem and no-op test have been there
for as long as this code has existed.

So, if these problems have been around for a while, how did I find them?
Only because I did a configure including these options:

$ ./configure --with-openssl --without-rustls
  SSL:              enabled (OpenSSL)

and got this diagnostic at the end:
WARNING: rustls enabled but marked EXPERIMENTAL. Use with caution!

I've tested these changes by running various combinations of options,
and checking that the diagnostic at the end prints correctly. e.g.:

$ ./configure --without-ssl
  SSL:              no      (--with-{openssl,gnutls,nss,mbedtls,wolfssl,schannel,secure-transport,amissl,bearssl,rustls} )

$ ./configure --with-openssl
  SSL:              enabled (OpenSSL)

$ ./configure --with-openssl --with-gnutls
  SSL:              enabled (OpenSSL, GnuTLS)

[bagder]

👍 nice work!

[bagder]

Thanks!