pref: fix cross-compiling graphical apps to Windows (#7449)

.github/workflows/ci.yml

@@ -153,6 +153,7 @@ jobs:
         brew install postgresql
         brew install glfw
         ## brew install sdl2 sdl2_ttf sdl2_mixer sdl2_image
+        brew install mingw-w64
         export LIBRARY_PATH="$LIBRARY_PATH:/usr/local/opt/openssl/lib/"
     - name: Build V
       run:  make -j4 && ./v -cg -cflags -Werror -o v cmd/v
@@ -189,7 +190,13 @@ jobs:
       run: |
         ./v doctor
     - name: Cross-compilation to Linux
-      run: ./v -os linux cmd/v
+      run: |
+        ./v -os linux cmd/v
+        # TODO: fix this: ./v -os linux examples/2048/2048.v
+    - name: Cross-compilation to Windows
+      run: |
+        ./v -os windows cmd/v
+        ./v -os windows examples/2048/2048.v
 #    - name: Test vsh
 #      run:  ./v examples/v_script.vsh
     - name: Test ved
@@ -576,6 +583,10 @@ jobs:
         ./v -os windows examples/hello_world.v
         ls -lart examples/hello_world.exe
         wine examples/hello_world.exe
+    - name: 2048.v can be cross compiled to 2048.exe
+      run: |
+        ./v -os windows examples/2048/2048.v
+        ls -lart examples/2048/2048.exe
 
   ubuntu-c-plus-plus:
     runs-on: ubuntu-18.04

vlib/v/builder/cc.v

@@ -703,6 +703,9 @@ fn (mut v Builder) cc() {
 }
 
 fn (mut b Builder) cc_linux_cross() {
+	b.setup_ccompiler_options(b.pref.ccompiler)
+	b.build_thirdparty_obj_files()
+	b.setup_output_name()
 	parent_dir := os.vmodules_dir()
 	if !os.exists(parent_dir) {
 		os.mkdir(parent_dir)
@@ -763,6 +766,9 @@ fn (mut b Builder) cc_linux_cross() {
 
 fn (mut c Builder) cc_windows_cross() {
 	println('Cross compiling for Windows...')
+	c.setup_ccompiler_options(c.pref.ccompiler)
+	c.build_thirdparty_obj_files()
+	c.setup_output_name()
 	if !c.pref.out_name.ends_with('.exe') {
 		c.pref.out_name += '.exe'
 	}
@@ -865,12 +871,6 @@ fn (mut v Builder) build_thirdparty_obj_files() {
 
 fn (mut v Builder) build_thirdparty_obj_file(path string, moduleflags []cflag.CFlag) {
 	obj_path := os.real_path(path)
-	if v.pref.os == .windows {
-		// Cross compiling for Windows
-		$if !windows {
-			v.pref.ccompiler = mingw_cc
-		}
-	}
 	cfile := '${obj_path[..obj_path.len - 2]}.c'
 	btarget := moduleflags.c_options_before_target()
 	atarget := moduleflags.c_options_after_target()

vlib/v/parser/comptime.v

@@ -10,13 +10,6 @@ import v.table
 import v.token
 import vweb.tmpl
 
-// #flag darwin -I.
-const (
-	supported_platforms  = ['windows', 'macos', 'darwin', 'linux', 'freebsd', 'openbsd', 'netbsd',
-		'dragonfly', 'android', 'js', 'solaris', 'haiku', 'linux_or_macos']
-	supported_ccompilers = ['tinyc', 'clang', 'mingw', 'msvc', 'gcc']
-)
-
 // // #include, #flag, #v
 fn (mut p Parser) hash() ast.HashStmt {
 	mut pos := p.prev_tok.position()

vlib/v/pref/default.v

@@ -68,6 +68,7 @@ pub fn (mut p Preferences) fill_with_defaults() {
 	if p.ccompiler == '' {
 		p.ccompiler = default_c_compiler()
 	}
+	p.find_cc_if_cross_compiling()
 	p.ccompiler_type = cc_from_string(p.ccompiler)
 	p.is_test = p.path.ends_with('_test.v')
 	p.is_vsh = p.path.ends_with('.vsh')
@@ -98,6 +99,21 @@ pub fn (mut p Preferences) fill_with_defaults() {
 	// p.use_cache = os.user_os() != 'windows'
 }
 
+fn (mut p Preferences) find_cc_if_cross_compiling() {
+	if p.os == .windows {
+		$if !windows {
+			// Cross compiling to Windows
+			p.ccompiler = 'x86_64-w64-mingw32-gcc'
+		}
+	}
+	if p.os == .linux {
+		$if !linux {
+			// Cross compiling to Linux
+			p.ccompiler = 'clang'
+		}
+	}
+}
+
 fn (mut p Preferences) try_to_use_tcc_by_default() {
 	if p.ccompiler == 'tcc' {
 		p.ccompiler = default_tcc_compiler()