ast,parser,cgen: add a new ast.FnDecl field is_c_extern, set it during parsing, to be available in markused and checker too

cmd/tools/vast/vast.v

@@ -546,9 +546,12 @@ fn (t Tree) fn_decl(node ast.FnDecl) &Node {
 	mut obj := new_object()
 	obj.add_terse('ast_type', t.string_node('FnDecl'))
 	obj.add_terse('name', t.string_node(node.name))
+	obj.add_terse('short_name', t.string_node(node.short_name))
 	obj.add_terse('mod', t.string_node(node.mod))
 	obj.add_terse('is_deprecated', t.bool_node(node.is_deprecated))
 	obj.add_terse('is_pub', t.bool_node(node.is_pub))
+	obj.add_terse('is_c_variadic', t.bool_node(node.is_c_variadic))
+	obj.add_terse('is_c_extern', t.bool_node(node.is_c_extern))
 	obj.add_terse('is_variadic', t.bool_node(node.is_variadic))
 	obj.add('is_anon', t.bool_node(node.is_anon))
 	obj.add_terse('is_noreturn', t.bool_node(node.is_noreturn))
@@ -559,17 +562,23 @@ fn (t Tree) fn_decl(node ast.FnDecl) &Node {
 	obj.add_terse('is_exported', t.bool_node(node.is_exported))
 	obj.add('is_keep_alive', t.bool_node(node.is_keep_alive))
 	obj.add_terse('is_unsafe', t.bool_node(node.is_unsafe))
+	obj.add_terse('is_markused', t.bool_node(node.is_markused))
+	obj.add_terse('is_file_translated', t.bool_node(node.is_file_translated))
 	obj.add_terse('receiver', t.struct_field(node.receiver))
 	obj.add('receiver_pos', t.pos(node.receiver_pos))
 	obj.add_terse('is_method', t.bool_node(node.is_method))
+	obj.add_terse('is_static_type_method', t.bool_node(node.is_static_type_method))
 	obj.add('method_type_pos', t.pos(node.method_type_pos))
 	obj.add('method_idx', t.number_node(node.method_idx))
 	obj.add_terse('rec_mut', t.bool_node(node.rec_mut))
+	obj.add_terse('has_prev_newline', t.bool_node(node.has_prev_newline))
+	obj.add_terse('has_break_line', t.bool_node(node.has_break_line))
 	obj.add('rec_share', t.enum_node(node.rec_share))
 	obj.add_terse('language', t.enum_node(node.language))
 	obj.add('file_mode', t.enum_node(node.file_mode))
 	obj.add('no_body', t.bool_node(node.no_body))
 	obj.add('is_builtin', t.bool_node(node.is_builtin))
+	obj.add('file', t.string_node(node.file))
 	obj.add('is_direct_arr', t.bool_node(node.is_direct_arr))
 	obj.add('ctdefine_idx', t.number_node(node.ctdefine_idx))
 	obj.add('pos', t.pos(node.pos))

vlib/v/ast/ast.v

@@ -560,6 +560,7 @@ pub:
 	is_deprecated         bool
 	is_pub                bool
 	is_c_variadic         bool
+	is_c_extern           bool
 	is_variadic           bool
 	is_anon               bool
 	is_noreturn           bool        // true, when @[noreturn] is used on a fn

vlib/v/gen/c/fn.v

@@ -10,6 +10,9 @@ import v.util
 const c_fn_name_escape_seq = ['[', '_T_', ']', '']
 
 fn (mut g Gen) is_used_by_main(node ast.FnDecl) bool {
+	if node.is_c_extern {
+		return true
+	}
 	mut is_used_by_main := true
 	if g.pref.skip_unused {
 		fkey := node.fkey()
@@ -71,7 +74,7 @@ fn (mut g Gen) fn_decl(node ast.FnDecl) {
 	defer {
 		g.inside_c_extern = old_inside_c_extern
 	}
-	if node.language == .c && node.attrs.contains('c_extern') {
+	if node.language == .c && node.is_c_extern {
 		g.inside_c_extern = true
 	}
 

vlib/v/parser/fn.v

@@ -196,6 +196,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	mut is_noreturn := false
 	mut is_ctor_new := false
 	mut is_c2v_variadic := false
+	mut is_c_extern := false
 	mut is_markused := false
 	mut is_expand_simple_interpolation := false
 	mut comments := []ast.Comment{}
@@ -237,6 +238,9 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			'markused' {
 				is_markused = true
 			}
+			'c_extern' {
+				is_c_extern = true
+			}
 			'windows_stdcall' {
 				p.note_with_pos('the tag [windows_stdcall] has been deprecated, it will be an error after 2022-06-01, use `[callconv: stdcall]` instead',
 					p.tok.pos())
@@ -662,6 +666,7 @@ run them via `v file.v` instead',
 		is_pub:             is_pub
 		is_variadic:        is_variadic
 		is_c_variadic:      is_c_variadic
+		is_c_extern:        is_c_extern
 		is_main:            is_main
 		is_test:            is_test
 		is_keep_alive:      is_keep_alive