feat: initial implementation of flat_error

crates/bitwarden-error-macro/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "bitwarden-error-macro"
+version.workspace = true
+authors.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+homepage.workspace = true
+repository.workspace = true
+license-file.workspace = true
+keywords.workspace = true
+
+[dependencies]
+quote = "1.0.37"
+syn = "2.0.79"
+
+[dev-dependencies]
+bitwarden-error = { path = "../bitwarden-error" }
+
+[lib]
+proc-macro = true
+
+[lints]
+workspace = true

crates/bitwarden-error-macro/src/lib.rs

@@ -0,0 +1,51 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, Data, DeriveInput, Fields};
+
+#[proc_macro_derive(FlatError)]
+pub fn derive_flat_error(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    let name = &input.ident;
+
+    // Generate match arms without converting variant names to strings
+    let variant_matches: Vec<_> = if let Data::Enum(data_enum) = &input.data {
+        data_enum
+            .variants
+            .iter()
+            .map(|variant| {
+                let variant_ident = &variant.ident;
+                let message = match &variant.fields {
+                    Fields::Unnamed(_) | Fields::Named(_) => {
+                        format!("Error: {}", variant_ident)
+                    }
+                    Fields::Unit => {
+                        format!("{}", variant_ident)
+                    }
+                };
+                quote! {
+                    #name::#variant_ident { .. } => (stringify!(#variant_ident), #message),
+                }
+            })
+            .collect()
+    } else {
+        panic!("FlatError can only be derived for enums");
+    };
+
+    let expanded = quote! {
+        impl FlatError for #name {
+            fn get_variant(&self) -> &str {
+                match self {
+                    #(#variant_matches)*
+                }.0
+            }
+
+            fn get_message(&self) -> &str {
+                match self {
+                    #(#variant_matches)*
+                }.1
+            }
+        }
+    };
+
+    TokenStream::from(expanded)
+}

crates/bitwarden-error-macro/tests/mod.rs

@@ -0,0 +1,50 @@
+use bitwarden_error::prelude::*;
+
+#[test]
+fn flattens_basic_enums() {
+    #[derive(FlatError)]
+    enum Errors {
+        Foo,
+        Bar,
+        Baz,
+    }
+
+    let foo = Errors::Foo;
+    let bar = Errors::Bar;
+    let baz = Errors::Baz;
+
+    assert_eq!(foo.get_variant(), "Foo");
+    assert_eq!(bar.get_variant(), "Bar");
+    assert_eq!(baz.get_variant(), "Baz");
+
+    assert_eq!(foo.get_message(), "Foo");
+    assert_eq!(bar.get_message(), "Bar");
+    assert_eq!(baz.get_message(), "Baz");
+}
+
+#[test]
+fn flattens_enums_with_fields() {
+    #[derive(FlatError)]
+    enum Errors {
+        #[allow(dead_code)]
+        Foo(String),
+        #[allow(dead_code)]
+        Bar(u32),
+        Baz,
+    }
+
+    let foo = Errors::Foo("hello".to_string());
+    let bar = Errors::Bar(42);
+    let baz = Errors::Baz;
+
+    assert_eq!(foo.get_variant(), "Foo");
+    assert_eq!(bar.get_variant(), "Bar");
+    assert_eq!(baz.get_variant(), "Baz");
+
+    // The message is always "Error: <variant>"
+    // TODO: Add support for getting the message from the fields
+    // or maybe just remove get_message and rely on ToString
+    assert_eq!(foo.get_message(), "Error: Foo");
+    assert_eq!(bar.get_message(), "Error: Bar");
+    assert_eq!(baz.get_message(), "Baz");
+}

crates/bitwarden-error/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "bitwarden-error"
+version.workspace = true
+authors.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+homepage.workspace = true
+repository.workspace = true
+license-file.workspace = true
+keywords.workspace = true
+
+[dependencies]
+bitwarden-error-macro = { path = "../bitwarden-error-macro" }
+
+[lints]
+workspace = true

crates/bitwarden-error/src/flat_error.rs

@@ -0,0 +1,4 @@
+pub trait FlatError {
+    fn get_variant(&self) -> &str;
+    fn get_message(&self) -> &str;
+}

crates/bitwarden-error/src/lib.rs

@@ -0,0 +1,8 @@
+mod flat_error;
+
+pub use flat_error::FlatError;
+
+pub mod prelude {
+    pub use crate::FlatError;
+    pub use bitwarden_error_macro::FlatError;
+}