cgen: fix error for defining global anonymous functions (#13808)

Author: yuyi98

vlib/v/gen/c/cgen.v

@@ -4360,6 +4360,13 @@ fn (mut g Gen) global_decl(node ast.GlobalDecl) {
 			}
 		}
 		styp := g.typ(field.typ)
+		mut anon_fn_expr := unsafe { field.expr }
+		if field.has_expr && mut anon_fn_expr is ast.AnonFn {
+			g.gen_anon_fn_decl(mut anon_fn_expr)
+			fn_type_name := g.get_anon_fn_type_name(mut anon_fn_expr, field.name)
+			g.definitions.writeln('$fn_type_name = ${g.table.sym(field.typ).name}; // global')
+			continue
+		}
 		g.definitions.write_string('$visibility_kw$styp $attributes $field.name')
 		if field.has_expr {
 			if field.expr.is_literal() && should_init {

vlib/v/gen/c/fn.v

@@ -612,6 +612,25 @@ fn (mut g Gen) fn_decl_params(params []ast.Param, scope &ast.Scope, is_variadic
 	return fargs, fargtypes, heap_promoted
 }
 
+fn (mut g Gen) get_anon_fn_type_name(mut node ast.AnonFn, var_name string) string {
+	mut builder := strings.new_builder(64)
+	return_styp := g.typ(node.decl.return_type)
+	builder.write_string('$return_styp (*$var_name) (')
+	if node.decl.params.len == 0 {
+		builder.write_string('void)')
+	} else {
+		for i, param in node.decl.params {
+			param_styp := g.typ(param.typ)
+			builder.write_string('$param_styp $param.name')
+			if i != node.decl.params.len - 1 {
+				builder.write_string(', ')
+			}
+		}
+		builder.write_string(')')
+	}
+	return builder.str()
+}
+
 fn (mut g Gen) call_expr(node ast.CallExpr) {
 	// g.write('/*call expr*/')
 	// NOTE: everything could be done this way

vlib/v/tests/init_global_test.v

@@ -53,6 +53,11 @@ fn test_no_type() {
 	assert testmap['asd'] == -7.25
 }
 
+fn test_fn_type() {
+	assert func2(22) == 22
+	assert func3(22) == '22'
+}
+
 __global (
 	intmap    map[string]int
 	numberfns map[string]fn () int
@@ -75,6 +80,13 @@ __global (
 		'asd': -7.25
 		'yxc': 3.125
 	}
+	func1     = fn () {}
+	func2     = fn (n int) int {
+		return n
+	}
+	func3     = fn (n int) string {
+		return '$n'
+	}
 )
 
 fn init() {