cgen: fix fntype unwrap on ifguard (fix #25911) (#25914)

Author: felipensp

vlib/v/gen/c/assign.v

@@ -799,32 +799,7 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 					ret_styp := g.styp(g.unwrap_generic(val_type))
 					g.write('${ret_styp} ${fn_name}')
 				} else {
-					ret_styp := g.styp(right_sym.info.func.return_type)
-					mut call_conv := ''
-					mut msvc_call_conv := ''
-					for attr in right_sym.info.func.attrs {
-						match attr.name {
-							'callconv' {
-								if g.is_cc_msvc {
-									msvc_call_conv = '__${attr.arg} '
-								} else {
-									call_conv = '${attr.arg}'
-								}
-							}
-							else {}
-						}
-					}
-					call_conv_attribute_suffix := if call_conv.len != 0 {
-						'__attribute__((${call_conv}))'
-					} else {
-						''
-					}
-					g.write('${ret_styp} (${msvc_call_conv}*${fn_name}) (')
-					def_pos := g.definitions.len
-					g.fn_decl_params(right_sym.info.func.params, unsafe { nil }, false,
-						false)
-					g.definitions.go_back(g.definitions.len - def_pos)
-					g.write(')${call_conv_attribute_suffix}')
+					g.write_fntype_decl(fn_name, right_sym.info)
 				}
 			} else {
 				if is_decl {

vlib/v/gen/c/fn.v

@@ -3050,3 +3050,31 @@ fn (mut g Gen) write_fn_attrs(attrs []ast.Attr) string {
 fn call_convention_attribute(cconvention string, is_cc_msvc bool) string {
 	return if is_cc_msvc { '__${cconvention} ' } else { '__attribute__((${cconvention})) ' }
 }
+
+fn (mut g Gen) write_fntype_decl(fn_name string, info ast.FnType) {
+	ret_styp := g.styp(info.func.return_type)
+	mut call_conv := ''
+	mut msvc_call_conv := ''
+	for attr in info.func.attrs {
+		match attr.name {
+			'callconv' {
+				if g.is_cc_msvc {
+					msvc_call_conv = '__${attr.arg} '
+				} else {
+					call_conv = '${attr.arg}'
+				}
+			}
+			else {}
+		}
+	}
+	call_conv_attribute_suffix := if call_conv.len != 0 {
+		'__attribute__((${call_conv}))'
+	} else {
+		''
+	}
+	g.write('${ret_styp} (${msvc_call_conv}*${fn_name}) (')
+	def_pos := g.definitions.len
+	g.fn_decl_params(info.func.params, unsafe { nil }, false, false)
+	g.definitions.go_back(g.definitions.len - def_pos)
+	g.write(')${call_conv_attribute_suffix}')
+}

vlib/v/gen/c/if.v

@@ -395,7 +395,13 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 							} else {
 								'-> '
 							}
-							g.writeln('\t${base_type} ${left_var_name} = *(${base_type}*)${var_name}${dot_or_ptr}data;')
+							expr_sym := g.table.sym(branch.cond.expr_type)
+							if expr_sym.info is ast.FnType {
+								g.write_fntype_decl(left_var_name, expr_sym.info)
+							} else {
+								g.write('\t${base_type} ${left_var_name}')
+							}
+							g.writeln(' = *(${base_type}*)${var_name}${dot_or_ptr}data;')
 						}
 					} else if branch.cond.vars.len > 1 {
 						sym := g.table.sym(branch.cond.expr_type)

vlib/v/tests/options/option_fn_guard_test.v

@@ -0,0 +1,21 @@
+type MyFn = fn ()
+
+fn hello() {
+	println(@FN)
+}
+
+fn get_ptr() ?&MyFn {
+	return &hello
+}
+
+fn test_main() {
+	if p := get_ptr() {
+		assert voidptr(p) == voidptr(hello)
+		dump(p)
+		p()
+	}
+
+	p2 := get_ptr() or { return }
+	p2()
+	assert voidptr(p2) == voidptr(hello)
+}