feature (backend-rs, macro-rs): prittify error outputs for napi export

Co-authored-by: sup39 <dev@sup39.dev>

packages/backend-rs/src/util/error_chain.rs

@@ -0,0 +1,90 @@
+//! Error formatter used until backtracing methods are standarized
+
+use std::error::Error;
+
+/// Prettifies [`Error`] message (mainly for napi export)
+pub fn format_error(mut error: &dyn Error) -> String {
+    let mut to_return = String::new();
+
+    to_return.push_str(&format!(
+        concat!("      raw: {0:?}", "\n", "  message: {0}"),
+        error,
+    ));
+
+    while let Some(source) = error.source() {
+        to_return.push('\n');
+        to_return.push_str(&format!("caused by: {}", source));
+        error = source;
+    }
+
+    to_return
+}
+
+#[cfg(test)]
+mod unit_test {
+    use pretty_assertions::assert_eq;
+
+    #[test]
+    fn format_error() {
+        #[derive(thiserror::Error, Debug)]
+        #[error("inner error 1")]
+        struct InnerError1;
+
+        #[derive(thiserror::Error, Debug)]
+        #[error("unexpected string '{0}'")]
+        struct InnerError2(String);
+
+        #[derive(thiserror::Error, Debug)]
+        enum ErrorVariants {
+            #[error("error 1 occured")]
+            Error1(#[from] InnerError1),
+            #[error("error 2 occured")]
+            Error2(#[from] InnerError2),
+        }
+
+        fn causes_inner_error_1() -> Result<(), InnerError1> {
+            Err(InnerError1)
+        }
+        fn causes_inner_error_2() -> Result<(), InnerError2> {
+            Err(InnerError2("foo".to_string()))
+        }
+
+        fn causes_error_1() -> Result<(), ErrorVariants> {
+            causes_inner_error_1()?;
+            Ok(())
+        }
+        fn causes_error_2() -> Result<(), ErrorVariants> {
+            causes_inner_error_2()?;
+            Ok(())
+        }
+
+        let error_1 = causes_error_1().unwrap_err();
+        let error_2 = causes_error_2().unwrap_err();
+
+        let error_message_1 = super::format_error(&error_1);
+        let error_message_2 = super::format_error(&error_2);
+
+        // We can't assume consistency in `Debug` output, so the output texts
+        // may need to be updated in the future, and we shouldn't make this kind
+        // of assumption in the actual program.
+        let expected_message_1 = "
+      raw: Error1(InnerError1)
+  message: error 1 occured
+caused by: inner error 1
+";
+        let expected_message_2 = r#"
+      raw: Error2(InnerError2("foo"))
+  message: error 2 occured
+caused by: unexpected string 'foo'
+"#;
+
+        assert_eq!(
+            error_message_1,
+            expected_message_1[1..expected_message_1.len() - 1]
+        );
+        assert_eq!(
+            error_message_2,
+            expected_message_2[1..expected_message_2.len() - 1]
+        );
+    }
+}

packages/backend-rs/src/util/mod.rs

@@ -1,5 +1,6 @@
 //! Basic utilities such as ID generator and HTTP client
 
+pub mod error_chain;
 pub mod http_client;
 pub mod id;
 pub mod random;

packages/macro-rs/src/lib.rs

@@ -212,7 +212,7 @@ pub fn ts_export(
 /// ```
 ///
 /// ## Function with `Result<T, E>` return type
-/// ```
+/// ```ignore
 /// #[derive(thiserror::Error, Debug)]
 /// pub enum IntegerDivisionError {
 ///     #[error("Divided by zero")]
@@ -233,7 +233,7 @@ pub fn ts_export(
 /// }
 /// ```
 /// generates
-/// ```
+/// ```ignore
 /// # #[derive(thiserror::Error, Debug)]
 /// # pub enum IntegerDivisionError {
 /// #     #[error("Divided by zero")]
@@ -252,7 +252,7 @@ pub fn ts_export(
 /// # }
 /// #[napi_derive::napi(js_name = "integerDivide",)]
 /// pub fn integer_divide_napi(dividend: i64, divisor: i64) -> napi::Result<i64> {
-///     integer_divide(dividend, divisor).map_err(|err| napi::Error::from_reason(err.to_string()))
+///     integer_divide(dividend, divisor).map_err(|err| napi::Error::from_reason(crate::util::error_chain::format_error(&err)))
 /// }
 /// ```
 #[proc_macro_attribute]
@@ -329,7 +329,7 @@ fn napi_impl(macro_attr: TokenStream, item: TokenStream) -> TokenStream {
             };
             // add modifier to function call result
             function_call_modifiers.push(quote! {
-                .map_err(|err| napi::Error::from_reason(err.to_string()))
+                .map_err(|err| napi::Error::from_reason(crate::util::error_chain::format_error(&err)))
             });
         }
     };
@@ -539,7 +539,7 @@ mod tests {
                     divisor: i64,
                 ) -> napi::Result<i64> {
                     integer_divide(dividend, divisor)
-                        .map_err(|err| napi::Error::from_reason(err.to_string()))
+                        .map_err(|err| napi::Error::from_reason(crate::util::error_chain::format_error(&err)))
                 }
             }
         );