configure: prepare for auto-generated option parsing

Prepare the configure script and Makefile for automatically generated
help and parsing.

Because we need to run the script to generate the full help, we
cannot rely on the user supplying the path to a Python interpreter
with --python; therefore, the introspection output is parsed into
shell functions and stored in scripts/.  The converter is written
in Python as standard for QEMU, and this commit contains a stub.

Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20211007130829.632254-18-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -87,7 +87,7 @@ x := $(shell rm -rf meson-private meson-info meson-logs)
 endif
 
 # 1. ensure config-host.mak is up-to-date
-config-host.mak: $(SRC_PATH)/configure $(SRC_PATH)/pc-bios $(SRC_PATH)/VERSION
+config-host.mak: $(SRC_PATH)/configure $(SRC_PATH)/scripts/meson-buildoptions.sh $(SRC_PATH)/pc-bios $(SRC_PATH)/VERSION
 	@echo config-host.mak is out-of-date, running configure
 	@if test -f meson-private/coredata.dat; then \
 	  ./config.status --skip-meson; \
@@ -124,6 +124,12 @@ ifneq ($(MESON),)
 Makefile.mtest: build.ninja scripts/mtest2make.py
 	$(MESON) introspect --targets --tests --benchmarks | $(PYTHON) scripts/mtest2make.py > $@
 -include Makefile.mtest
+
+.PHONY: update-buildoptions
+all update-buildoptions: $(SRC_PATH)/scripts/meson-buildoptions.sh
+$(SRC_PATH)/scripts/meson-buildoptions.sh: $(SRC_PATH)/meson_options.txt
+	$(MESON) introspect --buildoptions $(SRC_PATH)/meson.build | $(PYTHON) \
+	  scripts/meson-buildoptions.py > $@.tmp && mv $@.tmp $@
 endif
 
 # 4. Rules to bridge to other makefiles

configure

@@ -789,6 +789,18 @@ fi
 
 werror=""
 
+. $source_path/scripts/meson-buildoptions.sh
+
+meson_options=
+meson_option_parse() {
+  meson_options="$meson_options $(_meson_option_parse "$@")"
+  if test $? -eq 1; then
+    echo "ERROR: unknown option $1"
+    echo "Try '$0 --help' for more information"
+    exit 1
+  fi
+}
+
 for opt do
   optarg=$(expr "x$opt" : 'x[^=]*=\(.*\)')
   case "$opt" in
@@ -1548,6 +1560,8 @@ for opt do
   ;;
   --disable-slirp-smbd) slirp_smbd=no
   ;;
+  --enable-* | --disable-*) meson_option_parse "$opt" "$optarg"
+  ;;
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1804,11 +1818,9 @@ Advanced options (experts only):
                            enable plugins via shared library loading
   --disable-containers     don't use containers for cross-building
   --gdb=GDB-path           gdb to use for gdbstub tests [$gdb_bin]
-
-Optional features, enabled with --enable-FEATURE and
-disabled with --disable-FEATURE, default is enabled if available
-(unless built with --without-default-features):
-
+EOF
+  meson_options_help
+cat << EOF
   system          all system emulation targets
   user            supported user emulation targets
   linux-user      all linux usermode emulation targets
@@ -4489,7 +4501,8 @@ if test "$skip_meson" = no; then
   mv $cross config-meson.cross
 
   rm -rf meson-private meson-info meson-logs
-  NINJA=$ninja $meson setup \
+  run_meson() {
+    NINJA=$ninja $meson setup \
         --prefix "$prefix" \
         --libdir "$libdir" \
         --libexecdir "$libexecdir" \
@@ -4534,9 +4547,9 @@ if test "$skip_meson" = no; then
         -Dpa=$pa -Daudio_drv_list=$audio_drv_list -Dtcg_interpreter=$tcg_interpreter \
         -Dtrace_backends=$trace_backends -Dtrace_file=$trace_file -Dlinux_aio=$linux_aio \
         -Dnetmap=$netmap -Dvde=$vde \
-        $cross_arg \
-        "$PWD" "$source_path"
-
+        "$@" $cross_arg "$PWD" "$source_path"
+  }
+  eval run_meson $meson_options
   if test "$?" -ne 0 ; then
       error_exit "meson setup failed"
   fi

scripts/meson-buildoptions.py

@@ -0,0 +1,64 @@
+#! /usr/bin/env python3
+
+# Generate configure command line options handling code, based on Meson's
+# user build options introspection data
+#
+# Copyright (C) 2021 Red Hat, Inc.
+#
+# Author: Paolo Bonzini <pbonzini@redhat.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import json
+import textwrap
+import shlex
+import sys
+
+def sh_print(line=""):
+    print('  printf "%s\\n"', shlex.quote(line))
+
+
+def load_options(json):
+    json = [
+        x
+        for x in json
+        if x["section"] == "user"
+        and ":" not in x["name"]
+        and x["name"] not in SKIP_OPTIONS
+    ]
+    return sorted(json, key=lambda x: x["name"])
+
+
+def print_help(options):
+    print("meson_options_help() {")
+    sh_print()
+    sh_print("Optional features, enabled with --enable-FEATURE and")
+    sh_print("disabled with --disable-FEATURE, default is enabled if available")
+    sh_print("(unless built with --without-default-features):")
+    sh_print()
+    print("}")
+
+
+def print_parse(options):
+    print("_meson_option_parse() {")
+    print("  case $1 in")
+    print("    *) return 1 ;;")
+    print("  esac")
+    print("}")
+
+
+options = load_options(json.load(sys.stdin))
+print("# This file is generated by meson-buildoptions.py, do not edit!")
+print_help(options)
+print_parse(options)

scripts/meson-buildoptions.sh

@@ -0,0 +1,13 @@
+# This file is generated by meson-buildoptions.py, do not edit!
+meson_options_help() {
+  printf "%s\n" ''
+  printf "%s\n" 'Optional features, enabled with --enable-FEATURE and'
+  printf "%s\n" 'disabled with --disable-FEATURE, default is enabled if available'
+  printf "%s\n" '(unless built with --without-default-features):'
+  printf "%s\n" ''
+}
+_meson_option_parse() {
+  case $1 in
+    *) return 1 ;;
+  esac
+}