gen: fix assigning an anon fn to a struct field (#6965)

vlib/v/gen/cgen.v

@@ -1522,8 +1522,8 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 		g.write('static ')
 	}
 	mut return_type := table.void_type
-	op := if assign_stmt.op == .decl_assign { token.Kind.assign } else { assign_stmt.op }
 	is_decl := assign_stmt.op == .decl_assign
+	op := if is_decl { token.Kind.assign } else { assign_stmt.op }
 	right_expr := assign_stmt.right[0]
 	match right_expr {
 		ast.CallExpr { return_type = right_expr.return_type }
@@ -1756,12 +1756,18 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 				if blank_assign {
 					g.write('{')
 				}
+				// if it's a decl assign (`:=`) or a blank assignment `_ =`/`_ :=` then generate `void (*ident) (args) =`
+				if (is_decl || blank_assign) && left is ast.Ident {
 					ret_styp := g.typ(val.decl.return_type)
 					g.write('$ret_styp (*$ident.name) (')
 					def_pos := g.definitions.len
 					g.fn_args(val.decl.params, val.decl.is_variadic)
 					g.definitions.go_back(g.definitions.len - def_pos)
 					g.write(') = ')
+				} else {
+					g.expr(left)
+					g.write(' = ')
+				}
 				g.expr(val)
 				g.writeln(';')
 				if blank_assign {

vlib/v/tests/anon_fn_test.v

@@ -8,3 +8,16 @@ fn test_go_anon_fn() {
 	}(mut wg)
 	wg.wait()
 }
+
+struct AnonFnWrapper {
+mut:
+	fn_ fn () bool
+}
+
+fn test_anon_assign_struct() {
+	mut w := AnonFnWrapper{}
+	w.fn_ = fn () bool {
+		return true
+	}
+	assert w.fn_()
+}