feat(log): add bounded diagnostic transport

libs/kaptan-log-derive/tests/ui.rs

@@ -0,0 +1,7 @@
+#[test]
+fn kaptan_error_expands_for_enum_shapes_only() {
+    let tests = trybuild::TestCases::new();
+    tests.pass("tests/ui/enum.rs");
+    tests.compile_fail("tests/ui/struct.rs");
+    tests.compile_fail("tests/ui/union.rs");
+}

libs/kaptan-log-derive/tests/ui/enum.rs

@@ -0,0 +1,47 @@
+extern crate self as kaptan_log;
+
+use kaptan_log_derive::KaptanError;
+
+pub struct StaticErrorMessage(&'static str);
+
+impl StaticErrorMessage {
+    pub const fn new(text: &'static str) -> Self {
+        Self(text)
+    }
+
+    pub const fn as_str(&self) -> &'static str {
+        self.0
+    }
+}
+
+pub trait ErrorReport {
+    fn error_message(&self) -> &'static StaticErrorMessage;
+}
+
+#[derive(Debug, KaptanError)]
+enum Generic<'a, T>
+where
+    T: Copy,
+{
+    Unit,
+    Tuple(T, u8),
+    Named { label: &'a str },
+}
+
+fn main() {
+    fn assert_error<T: core::error::Error>() {}
+    assert_error::<Generic<'_, u8>>();
+    assert_eq!(
+        Generic::<u8>::Unit.error_message().as_str(),
+        concat!(module_path!(), "::Generic::Unit"),
+    );
+    assert_eq!(
+        Generic::Tuple(1_u8, 2).error_message().as_str(),
+        concat!(module_path!(), "::Generic::Tuple"),
+    );
+    let named: Generic<'_, u8> = Generic::Named { label: "test" };
+    assert_eq!(
+        named.to_string(),
+        concat!(module_path!(), "::Generic::Named"),
+    );
+}

libs/kaptan-log-derive/tests/ui/struct.rs

@@ -0,0 +1,8 @@
+use kaptan_log_derive::KaptanError;
+
+#[derive(KaptanError)]
+struct NotAnError {
+    code: u8,
+}
+
+fn main() {}

libs/kaptan-log-derive/tests/ui/struct.stderr

@@ -0,0 +1,5 @@
+error: KaptanError can only be derived for enums, not structs
+ --> tests/ui/struct.rs:4:8
+  |
+4 | struct NotAnError {
+  |        ^^^^^^^^^^

libs/kaptan-log-derive/tests/ui/union.rs

@@ -0,0 +1,8 @@
+use kaptan_log_derive::KaptanError;
+
+#[derive(KaptanError)]
+union NotAnError {
+    code: u8,
+}
+
+fn main() {}

libs/kaptan-log-derive/tests/ui/union.stderr

@@ -0,0 +1,5 @@
+error: KaptanError can only be derived for enums, not unions
+ --> tests/ui/union.rs:4:7
+  |
+4 | union NotAnError {
+  |       ^^^^^^^^^^