checker: fix `x := match enumexpr { .case2 { fn1 } .case2 { fn2} }`, where fn1 and fn2 have compatible signature

vlib/v/checker/checker.v

@@ -4071,8 +4071,11 @@ pub fn (mut c Checker) match_expr(mut node ast.MatchExpr) table.Type {
 						ret_type = expr_type
 						stmt.typ = ret_type
 					} else if node.is_expr && ret_type != expr_type {
-						sym := c.table.get_type_symbol(ret_type)
-						c.error('return type mismatch, it should be `$sym.name`', stmt.expr.position())
+						if !c.check_types(ret_type, expr_type) {
+							ret_sym := c.table.get_type_symbol(ret_type)
+							c.error('return type mismatch, it should be `$ret_sym.name`',
+								stmt.expr.position())
+						}
 					}
 				}
 				else {

vlib/v/tests/match_expression_with_fn_names_in_branches_test.v

@@ -0,0 +1,63 @@
+import math
+
+const tau = 2 * math.pi
+
+struct Note {
+mut:
+	freq   f32
+	vol    f32
+	step   int
+	paused bool
+}
+
+enum WaveKind {
+	sine
+	sawtooth
+}
+
+struct Config {
+	wave_kind WaveKind
+}
+
+fn sawtooth(note &Note, time f32, amp f32) f32 {
+	t := time * note.freq
+	f := t - int(t)
+	return f32(2 * (f - 0.5)) * (amp / 2)
+}
+
+fn sine(note &Note, time f32, amp f32) f32 {
+	return math.sinf(tau * time * note.freq) * amp
+}
+
+pub fn new_context(cfg Config) fn (&Note, f32, f32) f32 {
+	// Note, that here `sine` and `sawtooth`,
+	// are different functions, but they do have
+	// a compatible signature, so `next_fn` can 
+	// become either one of them:
+	next_fn := match cfg.wave_kind {
+		.sine { sine }
+		.sawtooth { sawtooth }
+	}
+	return next_fn
+}
+
+fn test_match_expression_returning_fns() {
+	note := &Note{
+		freq: 432
+		vol: 80
+		step: 3
+		paused: false
+	}
+
+	x := new_context(wave_kind: .sawtooth)
+	assert '$x' == 'fn (Note, f32, f32) f32'
+	assert math.abs(x(note, 0, 0.5) + 0.25) < 0.001
+	assert math.abs(x(note, 0.4, 0.5) - 0.15) < 0.001
+	assert math.abs(x(note, 0.7, 0.5) + 0.05) < 0.001
+
+	y := new_context(wave_kind: .sine)
+	assert '$y' == 'fn (Note, f32, f32) f32'
+	assert math.abs(y(note, 0, 0.5)) - 0.475 < 0.0001
+	assert math.abs(y(note, 0.4, 0.5)) - 0.4755 < 0.0001
+	assert math.abs(y(note, 0.7, 0.5)) - 0.2939 < 0.0001
+}