Add UI tests for custom error

nutype_macros/src/common/parse/mod.rs

@@ -183,11 +183,11 @@ where
         match (validators.len(), maybe_with, maybe_error) {
             (0, Some(with), Some(error)) => Ok(RawValidation::Custom { with, error }),
             (0, Some(_), None) => {
-                let msg = "`with` attribute must be used with `error` attribute";
+                let msg = "The `with` attribute requires an accompanying `error` attribute.\nPlease provide the error type that the `with` validation function returns.";
                 Err(syn::Error::new(input.span(), msg))
             }
-            (0, None, Some(_)) => {
-                let msg = "`error` attribute must be used with `with` attribute";
+            (0, None, Some(error_type)) => {
+                let msg = format!("The `error` attribute requires an accompanying `with` attribute.\nPlease provide the validation function that returns Result<(), {error_type}>.");
                 Err(syn::Error::new(input.span(), msg))
             }
             (0, None, None) => {
@@ -197,7 +197,7 @@ where
             (_, None, None) => Ok(RawValidation::Standard { validators }),
             (_, _, _) => {
                 let msg =
-                    "`with` and `error` attributes cannot be used mixed with other validators";
+                    "`with` and `error` attributes cannot be used mixed with other validators.";
                 Err(syn::Error::new(input.span(), msg))
             }
         }

test_suite/tests/ui/common/custom_validaiton_no_with.rs

@@ -0,0 +1,14 @@
+use nutype::nutype;
+
+#[nutype(
+    validate(error = NumError)
+)]
+pub struct Num(i32);
+
+#[derive(Debug)]
+enum NumError {
+    TooBig,
+    TooSmall,
+}
+
+fn main () {}

test_suite/tests/ui/common/custom_validaiton_no_with.stderr

@@ -0,0 +1,6 @@
+error: The `error` attribute requires an accompanying `with` attribute.
+       Please provide the validation function that returns Result<(), NumError>.
+ --> tests/ui/common/custom_validaiton_no_with.rs:4:30
+  |
+4 |     validate(error = NumError)
+  |                              ^

test_suite/tests/ui/common/custom_validation_mixed.rs

@@ -0,0 +1,24 @@
+use nutype::nutype;
+
+#[nutype(
+    validate(with = validate_num, error = NumError, predicate = |val| *val > 0 )
+)]
+pub struct Num(i32);
+
+fn validate_num(val: &i32) -> Result<(), NumError> {
+    if *val > 100 {
+        Err(NumError::TooBig)
+    } else if *val < 0 {
+        Err(NumError::TooSmall)
+    } else {
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+enum NumError {
+    TooBig,
+    TooSmall,
+}
+
+fn main () {}

test_suite/tests/ui/common/custom_validation_mixed.stderr

@@ -0,0 +1,5 @@
+error: `with` and `error` attributes cannot be used mixed with other validators.
+ --> tests/ui/common/custom_validation_mixed.rs:4:80
+  |
+4 |     validate(with = validate_num, error = NumError, predicate = |val| *val > 0 )
+  |                                                                                ^

test_suite/tests/ui/common/custom_validation_no_error.stderr

@@ -0,0 +1,6 @@
+error: The `with` attribute requires an accompanying `error` attribute.
+       Please provide the error type that the `with` validation function returns.
+ --> tests/ui/common/custom_validation_no_error.rs:4:34
+  |
+4 |     validate(with = validate_num,)
+  |                                  ^