From 12dd6e8b39d3d24872b6a2de6f8c5c52f3bef3df Mon Sep 17 00:00:00 2001
From: Turiiya <34311583+ttytm@users.noreply.github.com>
Date: Sun, 10 Sep 2023 16:32:02 +0200
Subject: [PATCH] toml: add comptime check if a supported type (struct) was
 passed to `toml.decode`, when the type has no custom `.from_toml` method
 defined (#19317)

---
 vlib/toml/tests/encode_and_decode_test.v | 10 ++++++++++
 vlib/toml/toml.v                         |  3 +++
 2 files changed, 13 insertions(+)

diff --git a/vlib/toml/tests/encode_and_decode_test.v b/vlib/toml/tests/encode_and_decode_test.v
index 6f57bf7473..66e7192bf9 100644
--- a/vlib/toml/tests/encode_and_decode_test.v
+++ b/vlib/toml/tests/encode_and_decode_test.v
@@ -177,3 +177,13 @@ times = [
 	assert toml.encode[Arrs](a) == s
 	assert toml.decode[Arrs](s)! == a
 }
+
+fn test_unsupported_type() {
+	s := 'name = "Peter"'
+	err_msg := 'toml.decode: expected struct, found '
+	toml.decode[string](s) or { assert err.msg() == err_msg + 'string' }
+	toml.decode[[]string](s) or { assert err.msg() == err_msg + '[]string' }
+	toml.decode[int](s) or { assert err.msg() == err_msg + 'int' }
+	toml.decode[[]f32](s) or { assert err.msg() == err_msg + '[]f32' }
+	// ...
+}
diff --git a/vlib/toml/toml.v b/vlib/toml/toml.v
index ad94095c38..fea73da731 100644
--- a/vlib/toml/toml.v
+++ b/vlib/toml/toml.v
@@ -23,6 +23,9 @@ pub fn decode[T](toml_txt string) !T {
 			return typ
 		}
 	}
+	$if T !is $struct {
+		return error('toml.decode: expected struct, found ${T.name}')
+	}
 	decode_struct[T](doc.to_any(), mut typ)
 	return typ
 }