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The shell variables $as_echo and $as_echo_n and the substitution variables @ECHO_C@, @ECHO_N@, and @ECHO_T@ are implementation details of the old implementation of AS_ECHO and AS_ECHO_N (2.69-era; before the switch to use ‘printf’). We continue to provide them for compatibility with various third-party macros and Makefiles that used them, even though, as far as I can tell, they were never documented. (Someone made ECHO_C etc. substitution variables on purpose, though.) For $as_echo and $as_echo_n, we can tell precisely when they are needed, because all uses are exposed to M4 macro expansion. Therefore, emit the necessary support code on first use and not from AS_INIT. As a side effect this means the -Wobsolete warning only appears on the first use of each, which IMHO is polite. For @ECHO_C@, @ECHO_N@, and @ECHO_T@, we have no way of knowing whether a substitution variable is used, but we *do* know that substitution variables are exclusively a configure.ac thing, so their support code can be moved to general.m4 and emitted from AC_INIT rather than from AS_INIT. (It’s faintly possible that someone decided to use $ECHO_C in an Autotest script but considering how rare it is for people to use Autotest at all, or any other non-Autoconf application of M4sh, I think we can worry about that when we hear about it.) * lib/m4sugar/m4sh.m4 (_AS_ECHO_N_PREPARE): Removed. (AS_PREPARE, _AS_PREPARE): Don’t use _AS_ECHO_N_PREPARE. (_as_echo_var_prepare, _as_echo_n_var_prepare): New macros which emit the -Wobsolete warning and the support code for $as_echo and $as_echo_n respectively. (as_echo, as_echo_n): Move to bottom of the block that sets up the current implementation of AS_ECHO. Invoke _as_echo_var_prepare and _as_echo_n_var_prepare, respectively, on first use. * lib/autoconf/general.m4 (_AC_INIT_ECHO_N): New internal macro, contains the probe code that used to be in _AS_ECHO_N_PREPARE. AC_SUBSTs ECHO_C, ECHO_N, and ECHO_T. (AC_INIT): Don’t AC_SUBST ECHO_C, ECHO_N, and ECHO_T here. Invoke _AC_INIT_ECHO_N.
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