2 files changed, 74 insertions, 0 deletions

diff --git a/embassy-executor-macros/src/util/ctxt.rs b/embassy-executor-macros/src/util/ctxt.rs
new file mode 100644
index 000000000..74c872c3c
--- /dev/null
+++ b/embassy-executor-macros/src/util/ctxt.rs
@@ -0,0 +1,73 @@
+// nifty utility borrowed from serde :)
+// https://github.com/serde-rs/serde/blob/master/serde_derive/src/internals/ctxt.rs
+
+use std::cell::RefCell;
+use std::fmt::Display;
+use std::thread;
+
+use proc_macro2::TokenStream;
+use quote::{quote, ToTokens};
+use syn;
+
+/// A type to collect errors together and format them.
+///
+/// Dropping this object will cause a panic. It must be consumed using `check`.
+///
+/// References can be shared since this type uses run-time exclusive mut checking.
+#[derive(Default)]
+pub struct Ctxt {
+    // The contents will be set to `None` during checking. This is so that checking can be
+    // enforced.
+    errors: RefCell<Option<Vec<syn::Error>>>,
+}
+
+impl Ctxt {
+    /// Create a new context object.
+    ///
+    /// This object contains no errors, but will still trigger a panic if it is not `check`ed.
+    pub fn new() -> Self {
+        Ctxt {
+            errors: RefCell::new(Some(Vec::new())),
+        }
+    }
+
+    /// Add an error to the context object with a tokenenizable object.
+    ///
+    /// The object is used for spanning in error messages.
+    pub fn error_spanned_by<A: ToTokens, T: Display>(&self, obj: A, msg: T) {
+        self.errors
+            .borrow_mut()
+            .as_mut()
+            .unwrap()
+            // Curb monomorphization from generating too many identical methods.
+            .push(syn::Error::new_spanned(obj.into_token_stream(), msg));
+    }
+
+    /// Add one of Syn's parse errors.
+    #[allow(unused)]
+    pub fn syn_error(&self, err: syn::Error) {
+        self.errors.borrow_mut().as_mut().unwrap().push(err);
+    }
+
+    /// Consume this object, producing a formatted error string if there are errors.
+    pub fn check(self) -> Result<(), TokenStream> {
+        let errors = self.errors.borrow_mut().take().unwrap();
+        match errors.len() {
+            0 => Ok(()),
+            _ => Err(to_compile_errors(errors)),
+        }
+    }
+}
+
+fn to_compile_errors(errors: Vec<syn::Error>) -> proc_macro2::TokenStream {
+    let compile_errors = errors.iter().map(syn::Error::to_compile_error);
+    quote!(#(#compile_errors)*)
+}
+
+impl Drop for Ctxt {
+    fn drop(&mut self) {
+        if !thread::panicking() && self.errors.borrow().is_some() {
+            panic!("forgot to check for errors");
+        }
+    }
+}
diff --git a/embassy-executor-macros/src/util/mod.rs b/embassy-executor-macros/src/util/mod.rs
new file mode 100644
index 000000000..28702809e
--- /dev/null
+++ b/embassy-executor-macros/src/util/mod.rs
@@ -0,0 +1 @@
+pub mod ctxt;