configure: absorb python3-mako check.

This is a better place for such checks than the Makefile, and we'll likely
have more in future.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Makefile

@@ -271,13 +271,6 @@ check-hdr-include-order/%: %
 check-makefile:
 	@if [ x"$(CCANDIR)/config.h `find $(CCANDIR)/ccan -name '*.h' | grep -v /test/ | LC_ALL=C sort | tr '\n' ' '`" != x"$(CCAN_HEADERS) " ]; then echo CCAN_HEADERS incorrect; exit 1; fi
 
-# Check if they've installed 'mako' dependency, useful for
-# keeping your build from clobbering itself
-check-bolt-dependency:
-	@python3 -c "import mako"
-
-BOLT_DEPS += check-bolt-dependency
-
 # Experimental quotes quote the exact version.
 ifeq ($(EXPERIMENTAL_FEATURES),1)
 CHECK_BOLT_PREFIX=--prefix="BOLT-$(BOLTVERSION)"

configure

@@ -68,6 +68,22 @@ default_pytest()
     done
 }
 
+require()
+{
+    name="$1"
+    resolution="$2"
+    shift 2
+
+    echo -n "checking for $name... "
+    if "$@" 2>/dev/null; then
+	echo 'found'
+	return
+    fi
+    echo 'not found'
+    echo "$resolution" >&2
+    exit 1
+}
+
 default_valgrind_setting()
 {
     # Valgrind must accept all these options (might exit with error 7 though
@@ -209,6 +225,9 @@ if [ "$ASAN" = "1" ]; then
     fi
 fi
 
+# Doesn't set a var, but makes sure it exists
+require 'python3-mako' "You need the mako module for python3: see doc/INSTALL.md" python3 -c 'import mako'
+
 rm -f $CONFIG_VAR_FILE.$$
 $CONFIGURATOR --extra-tests --autotools-style --var-file=$CONFIG_VAR_FILE.$$ --header-file=$CONFIG_HEADER --configurator-cc="$CONFIGURATOR_CC" "$CC" ${CWARNFLAGS-$BASE_WARNFLAGS} $CDEBUGFLAGS $COPTFLAGS <<EOF
 var=HAVE_GOOD_LIBSODIUM