Add ui test of unsatisfied serde trait bound

Author: dtolnay

test_suite/tests/ui/on_unimplemented.rs

@@ -0,0 +1,23 @@
+use serde::de::Deserialize;
+use serde::ser::Serialize;
+
+fn to_string<T>(_: &T) -> String
+where
+ T: Serialize,
+{
+ unimplemented!()
+}
+
+fn from_str<'de, T>(_: &'de str) -> T
+where
+ T: Deserialize<'de>,
+{
+ unimplemented!()
+}
+
+struct MyStruct;
+
+fn main() {
+ to_string(&MyStruct);
+ let _: MyStruct = from_str("");
+}

test_suite/tests/ui/on_unimplemented.stderr

@@ -0,0 +1,51 @@
+error[E0277]: the trait bound `MyStruct: Serialize` is not satisfied
+ --> tests/ui/on_unimplemented.rs:21:15
+ |
+21 | to_string(&MyStruct);
+ | --------- ^^^^^^^^^ the trait `Serialize` is not implemented for `MyStruct`
+ | |
+ | required by a bound introduced by this call
+ |
+ = help: the following other types implement trait `Serialize`:
+ &'a T
+ &'a mut T
+ ()
+ (T,)
+ (T0, T1)
+ (T0, T1, T2)
+ (T0, T1, T2, T3)
+ (T0, T1, T2, T3, T4)
+ and $N others
+note: required by a bound in `to_string`
+ --> tests/ui/on_unimplemented.rs:6:8
+ |
+4 | fn to_string<T>(_: &T) -> String
+ | --------- required by a bound in this function
+5 | where
+6 | T: Serialize,
+ | ^^^^^^^^^ required by this bound in `to_string`
+
+error[E0277]: the trait bound `MyStruct: Deserialize<'_>` is not satisfied
+ --> tests/ui/on_unimplemented.rs:22:23
+ |
+22 | let _: MyStruct = from_str("");
+ | ^^^^^^^^^^^^ the trait `Deserialize<'_>` is not implemented for `MyStruct`
+ |
+ = help: the following other types implement trait `Deserialize<'de>`:
+ &'a Path
+ &'a [u8]
+ &'a str
+ ()
+ (T,)
+ (T0, T1)
+ (T0, T1, T2)
+ (T0, T1, T2, T3)
+ and $N others
+note: required by a bound in `from_str`
+ --> tests/ui/on_unimplemented.rs:13:8
+ |
+11 | fn from_str<'de, T>(_: &'de str) -> T
+ | -------- required by a bound in this function
+12 | where
+13 | T: Deserialize<'de>,
+ | ^^^^^^^^^^^^^^^^ required by this bound in `from_str`