Emit shim implementation on macro error

finchie

Sep 8, 2025, 6:50 AM

TFKGE6LRNSG2N5Z3LIITYG7WH2VOLWQO7AESTWRWV52BFHESU26AC

Dependencies

[2] OWXLFLRM Merge `cli_macros` shim into `fluent_embed`
[3] CESJ4CTO Move macro-specific code into `macro_impl` module
[4] 73C6NOJ7 Fix minimal `Localize` implementation on errors
[5] 7JPOCQEI Add explicit error handling for macro parsing
[6] LU6IFZFG Remove `std::io::Write` trait bound from `Localize`
[7] QJC4IQIT Refactor `Localize` functions to infallibly return `String`
[8] NEBSVXIA Apply Clippy fixes
[9] 6XEMHUGS Use full `Locale` instead of `LanguageIdentifier` subset
[10] RUCC2HKZ Rename from `fluent_embed` to `l10n_embed`
[11] EKXWNEPK Rename `Localize::message_for_locale` to `Localize::localize_for`
[12] RA3H7PWC Refactor `Localize` for performance
[13] PGBXJWIH Move `l10n_embed` re-exports into `macro_prelude` module
[14] LIO32J4B Fix compiler error when `expand` feature is disabled
[15] XGRU7WZE Add `expand` feature for proc-macro debugging
[*] O77KA6C4 Create `fluent_embed` crate

Change contents

edit in l10n_embed_derive/src/lib.rs at line 16

[3.5274]→[10.1870:1959](∅→∅),[10.1959]→[9.1709:1710](∅→∅),[3.5365]→[9.1709:1710](∅→∅)

// No errors found, emit the generated `l10n_embed::Localize` implementation
replacement in l10n_embed_derive/src/lib.rs at line 33

[3.5498]→[3.5498:5545](∅→∅),[3.5545]→[8.1243:1328](∅→∅)

// Emit the relevant error message
macro_impl::error::emit(error, &attribute_stream, &derive_input_stream);

[3.5498]

[2.906]

// Using the `proc_macro_error2` crate to generate errors ignores
// the token stream returned from this function, so use the `set_dummy` function
// to make sure a macro error is as self-contained as possible:
// - Derive input streams are not consumed, so structs/enums don't "disappear" when macro returns error
// - Generate a shim trait implementation when possible so that editor completions still work as expected
proc_macro_error2::set_dummy(
match syn::parse2::<syn::DeriveInput>(derive_input_stream.clone()) {
// Generate a minimal `Localize` implementation so the error is self-contained
Ok(derive_input) => {
let ident = derive_input.ident;
let (impl_generics, type_generics, where_clause) =
derive_input.generics.split_for_impl();
replacement in l10n_embed_derive/src/lib.rs at line 46

[2.907]→[4.0:91](∅→∅),[4.91]→[5.2117:2362](∅→∅)

// Generate a minimal `Localize` implementation so the error is self-contained
match syn::parse2::<syn::DeriveInput>(derive_input_stream.clone()) {
Ok(derive_input) => {
let ident = derive_input.ident;
quote! {
#derive_input_stream

[2.907]

[9.1794]

quote! {
#derive_input_stream
replacement in l10n_embed_derive/src/lib.rs at line 49

[9.1795]→[10.2022:2087](∅→∅),[10.2087]→[12.4287:4328](∅→∅),[6.476]→[5.2937:2976](∅→∅),[11.745]→[5.2937:2976](∅→∅),[7.1403]→[5.2937:2976](∅→∅),[12.4328]→[5.2937:2976](∅→∅),[5.2937]→[5.2937:2976](∅→∅),[5.2976]→[12.4329:4479](∅→∅),[7.1446]→[5.3194:3278](∅→∅),[12.4479]→[5.3194:3278](∅→∅),[5.3194]→[5.3194:3278](∅→∅)

impl ::l10n_embed::Localize for #ident {
fn localize(
&self,
context: &::l10n_embed::Context,
buffer: &mut String,
) {
unimplemented!("Encountered error in derive macro")

[9.1795]

[5.3278]

impl #impl_generics ::l10n_embed::Localize for #ident #type_generics #where_clause {
fn localize(
&self,
context: &::l10n_embed::Context,
buffer: &mut String,
) {
unimplemented!("Encountered error in derive macro")
}
replacement in l10n_embed_derive/src/lib.rs at line 60

[3.5945]→[9.1874:1892](∅→∅),[9.1892]→[5.3354:3505](∅→∅),[5.3354]→[5.3354:3505](∅→∅),[5.3505]→[3.5963:5977](∅→∅),[3.5963]→[3.5963:5977](∅→∅)

}
// Unable to fail gracefully if the ident is unknown, so just return the original input
Err(_) => derive_input_stream,
}

[3.5945]

[3.5977]

// Unable to implement Localize if the ident is unknown, so just return the original input
Err(_) => derive_input_stream.clone(),
},
);

// Emit the relevant error message
macro_impl::error::emit(error, &attribute_stream, &derive_input_stream);

// `proc_macro_error2` will output the relevant token stream, but the function still needs to return something
quote!()