Windows: Pass list of symbols to export to MSVC

Arrange for passing .def files with the lists of symbols to export from
DLLs when building on Windows with MSVC. Without this no symbols were
being exported at all.

The .def files are generated from the .map files at build time using
scripts/map-to-def, which avoids needing to maintain two different sets
of files.

meson.build

@@ -152,6 +152,7 @@ have_version_script = cc.links(
     name: '-Wl,--version-script',
 )
 
+map_to_def = find_program('scripts/map-to-def')
 
 # libxkbcommon.
 # Note: we use some yacc extensions, which work with either GNU bison
@@ -231,15 +232,25 @@ libxkbcommon_sources = [
     'src/utils.h',
 ]
 libxkbcommon_link_args = []
+libxkbcommon_link_deps = []
 if have_version_script
     libxkbcommon_link_args += '-Wl,--version-script=' + meson.source_root()/'xkbcommon.map'
+    libxkbcommon_link_deps += 'xkbcommon.map'
+elif cc.get_argument_syntax() == 'msvc'
+    libxkbcommon_def = custom_target('xkbcommon.def',
+        command: [map_to_def, '@INPUT@', '@OUTPUT@'],
+        input: 'xkbcommon.map',
+        output: 'kxbcommon.def',
+    )
+    libxkbcommon_link_deps += libxkbcommon_def
+    libxkbcommon_link_args += '/DEF:' + libxkbcommon_def.full_path()
 endif
 libxkbcommon = library(
     'xkbcommon',
     'xkbcommon/xkbcommon.h',
     libxkbcommon_sources,
     link_args: libxkbcommon_link_args,
-    link_depends: 'xkbcommon.map',
+    link_depends: libxkbcommon_link_deps,
     gnu_symbol_visibility: 'hidden',
     version: '0.0.0',
     install: true,
@@ -287,15 +298,25 @@ You can disable X11 support with -Denable-x11=false.''')
         'src/atom.c',
     ]
     libxkbcommon_x11_link_args = []
+    libxkbcommon_x11_link_deps = []
     if have_version_script
         libxkbcommon_x11_link_args += '-Wl,--version-script=' + meson.source_root()/'xkbcommon-x11.map'
+        libxkbcommon_x11_link_deps += 'xkbcommon-x11.map'
+    elif cc.get_argument_syntax() == 'msvc'
+        libxkbcommon_x11_def = custom_target('xkbcommon-x11.def',
+            command: [map_to_def, '@INPUT@', '@OUTPUT@'],
+            input: 'xkbcommon-x11.map',
+            output: 'xkbcommon-x11.def',
+        )
+        libxkbcommon_x11_link_deps += libxkbcommon_x11_def
+        libxkbcommon_x11_link_args += '/DEF:' + libxkbcommon_x11_def.full_path()
     endif
     libxkbcommon_x11 = library(
         'xkbcommon-x11',
         'xkbcommon/xkbcommon-x11.h',
         libxkbcommon_x11_sources,
         link_args: libxkbcommon_x11_link_args,
-        link_depends: 'xkbcommon-x11.map',
+        link_depends: libxkbcommon_x11_link_deps,
         gnu_symbol_visibility: 'hidden',
         version: '0.0.0',
         install: true,
@@ -336,15 +357,25 @@ if get_option('enable-xkbregistry')
         'src/util-list.c',
     ]
     libxkbregistry_link_args = []
+    libxkbregistry_link_deps = []
     if have_version_script
         libxkbregistry_link_args += '-Wl,--version-script=' + meson.source_root()/'xkbregistry.map'
+        libxkbregistry_link_deps += 'xkbregistry.map'
+    elif cc.get_argument_syntax() == 'msvc'
+        libxkbregistry_def = custom_target('xkbregistry.def',
+            command: [map_to_def, '@INPUT@', '@OUTPUT@'],
+            input: 'xkbregistry.map',
+            output: 'xkbregistry.def',
+        )
+        libxkbregistry_link_deps += libxkbregistry_def
+        libxkbregistry_link_args += '/DEF:' + libxkbregistry_def.full_path()
     endif
     libxkbregistry = library(
         'xkbregistry',
         'xkbcommon/xkbregistry.h',
         libxkbregistry_sources,
         link_args: libxkbregistry_link_args,
-        link_depends: 'xkbregistry.map',
+        link_depends: libxkbregistry_link_deps,
         gnu_symbol_visibility: 'hidden',
         dependencies: deps_libxkbregistry,
         version: '0.0.0',

scripts/map-to-def

@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+
+"""A script to generate MSVC Module-Definition files from version-script
+files (which are maintained manually)."""
+
+import re
+import sys
+import pathlib
+
+
+def symbols_from_map(path):
+    return re.findall(r'^\s+(r?xkb_.*);', path.read_text('utf-8'), re.MULTILINE)
+
+
+if 2 > len(sys.argv) > 3:
+    raise SystemExit("Usage: {} file.map [file.def]".format(sys.argv[0]))
+
+
+map_file = pathlib.Path(sys.argv[1])
+map_symbols = set(symbols_from_map(map_file))
+
+if len(sys.argv) == 3:
+    def_file = open(sys.argv[2], "w", encoding="utf-8")
+else:
+    def_file = sys.stdout
+
+def_file.write("LIBRARY {}\n".format(map_file.stem))
+def_file.write("EXPORTS\n")
+for symbol in sorted(map_symbols):
+    def_file.write("\t{}\n".format(symbol))