rust: pin-init: internal: add utility API for syn error handling

The API is similar to diagnostics handling in rustc and uses a
`ErrorGuaranteed` value to signify that an error has been emitted. It
supports both fatal errors (which abort the macro expansion immediately
by returning `Err(ErrorGuaranteed)`) and non-fatal ones at generation
time. These errors are appended to the token stream after generation has
finished normally. This allows giving good errors while still expanding
most of the code as expected to avoid the user encountering additional
errors (for example missing definitions).

Suggested-by: Gary Guo <gary@garyguo.net>
Tested-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
[ remove duplicate word in commit message - Benno ]
Signed-off-by: Benno Lossin <lossin@kernel.org>

diff --git a/rust/pin-init/internal/src/diagnostics.rs b/rust/pin-init/internal/src/diagnostics.rs
new file mode 100644 (file)
index 0000000..555876c
--- /dev/null
+++ b/rust/pin-init/internal/src/diagnostics.rs
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use std::fmt::Display;
+
+use proc_macro2::TokenStream;
+use syn::{spanned::Spanned, Error};
+
+pub(crate) struct DiagCtxt(TokenStream);
+pub(crate) struct ErrorGuaranteed(());
+
+impl DiagCtxt {
+    #[expect(dead_code)]
+    pub(crate) fn error(&mut self, span: impl Spanned, msg: impl Display) -> ErrorGuaranteed {
+        let error = Error::new(span.span(), msg);
+        self.0.extend(error.into_compile_error());
+        ErrorGuaranteed(())
+    }
+
+    #[expect(dead_code)]
+    pub(crate) fn with(
+        fun: impl FnOnce(&mut DiagCtxt) -> Result<TokenStream, ErrorGuaranteed>,
+    ) -> TokenStream {
+        let mut dcx = Self(TokenStream::new());
+        match fun(&mut dcx) {
+            Ok(mut stream) => {
+                stream.extend(dcx.0);
+                stream
+            }
+            Err(ErrorGuaranteed(())) => dcx.0,
+        }
+    }
+}

diff --git a/rust/pin-init/internal/src/lib.rs b/rust/pin-init/internal/src/lib.rs
index 4c4dc639ce823d03dad3eae5ddd05e5c72cce2a5..0e1a4724549dfe17a82e759952ad4fccc4ffc869 100644 (file)
--- a/rust/pin-init/internal/src/lib.rs
+++ b/rust/pin-init/internal/src/lib.rs
@@ -12,6 +12,7 @@
 
 use proc_macro::TokenStream;
 
+mod diagnostics;
 mod helpers;
 mod pin_data;
 mod pinned_drop;