From 1654d8b8106b58cfe332152652c3b613728aa7a0 Mon Sep 17 00:00:00 2001
From: yuyi <yuyi98@163.com>
Date: Fri, 7 Jan 2022 00:33:37 +0800
Subject: [PATCH] checker: fix generics with nested generic fn inst call
 (#13059)

---
 vlib/v/checker/fn.v                           |  9 +++++-
 ...s_with_nested_generics_fn_inst_call_test.v | 30 +++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/generics_with_nested_generics_fn_inst_call_test.v

diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 3b25239ef8..1c002bd3a2 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -957,7 +957,14 @@ pub fn (mut c Checker) fn_call(mut node ast.CallExpr, mut continue_check &bool)
 			node.concrete_list_pos)
 	}
 	if func.generic_names.len > 0 {
-		return node.return_type
+		if has_generic {
+			return node.return_type
+		} else if typ := c.table.resolve_generic_to_concrete(func.return_type, func.generic_names,
+			concrete_types)
+		{
+			node.return_type = typ
+			return typ
+		}
 	}
 	return func.return_type
 }
diff --git a/vlib/v/tests/generics_with_nested_generics_fn_inst_call_test.v b/vlib/v/tests/generics_with_nested_generics_fn_inst_call_test.v
new file mode 100644
index 0000000000..16f66e4b75
--- /dev/null
+++ b/vlib/v/tests/generics_with_nested_generics_fn_inst_call_test.v
@@ -0,0 +1,30 @@
+fn test_generics_with_nested_generic_fn_inst_call() {
+	value := [byte(105), 116, 32, 119, 111, 114, 107, 115, 33, 33]
+	decoded := decode_arr<string>(value)
+	dump(decoded)
+	assert decoded.len == 4
+	assert decoded[0] == 'it works!!'
+	assert decoded[1] == 'it works!!'
+	assert decoded[2] == 'it works!!'
+	assert decoded[3] == 'it works!!'
+}
+
+fn decode_arr<T>(buf []byte) []T {
+	arr_size := decode<u32>(buf[0..4])
+	mut ret := []T{cap: int(arr_size)}
+
+	for _ in 0 .. arr_size {
+		ret << decode<T>(buf[..])
+	}
+	return ret
+}
+
+fn decode<T>(buf []byte) T {
+	$if T is u32 {
+		return u32(buf.len)
+	} $else $if T is string {
+		return buf.bytestr()
+	} $else {
+		panic('"$T.name" is not supported for `decode`')
+	}
+}