From 96f6a75bc82a9dabd25f84b917b5358244bd55a4 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Fri, 26 Jul 2024 06:13:30 +0000
Subject: [PATCH] add refutable pattern function macro
Signed-off-by: Jason Volk <jason@zemos.net>
---
src/macros/mod.rs | 4 +++
src/macros/refutable.rs | 61 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 65 insertions(+)
create mode 100644 src/macros/refutable.rs
diff --git a/src/macros/mod.rs b/src/macros/mod.rs
index b01e5275a..a0e61324a 100644
--- a/src/macros/mod.rs
+++ b/src/macros/mod.rs
@@ -1,6 +1,7 @@
mod admin;
mod cargo;
mod debug;
+mod refutable;
mod rustc;
mod utils;
@@ -19,3 +20,6 @@ pub fn recursion_depth(args: TokenStream, input: TokenStream) -> TokenStream { d
#[proc_macro]
pub fn rustc_flags_capture(args: TokenStream) -> TokenStream { rustc::flags_capture(args) }
+
+#[proc_macro_attribute]
+pub fn refutable(args: TokenStream, input: TokenStream) -> TokenStream { refutable::refutable(args, input) }
diff --git a/src/macros/refutable.rs b/src/macros/refutable.rs
new file mode 100644
index 000000000..6a6884e0e
--- /dev/null
+++ b/src/macros/refutable.rs
@@ -0,0 +1,61 @@
+use proc_macro::{Span, TokenStream};
+use quote::{quote, ToTokens};
+use syn::{parse_macro_input, AttributeArgs, FnArg::Typed, Ident, ItemFn, Pat, PatIdent, PatType, Stmt};
+
+pub(super) fn refutable(args: TokenStream, input: TokenStream) -> TokenStream {
+ let _args = parse_macro_input!(args as AttributeArgs);
+ let mut item = parse_macro_input!(input as ItemFn);
+
+ let inputs = item.sig.inputs.clone();
+ let stmt = &mut item.block.stmts;
+ let sig = &mut item.sig;
+ for (i, input) in inputs.iter().enumerate() {
+ let Typed(PatType {
+ pat,
+ ..
+ }) = input
+ else {
+ continue;
+ };
+
+ let Pat::Struct(ref pat) = **pat else {
+ continue;
+ };
+
+ let variant = &pat.path;
+ let fields = &pat.fields;
+
+ // new versions of syn can replace this kronecker kludge with get_mut()
+ for (j, input) in sig.inputs.iter_mut().enumerate() {
+ if i != j {
+ continue;
+ }
+
+ let Typed(PatType {
+ ref mut pat,
+ ..
+ }) = input
+ else {
+ continue;
+ };
+
+ let name = format!("_args_{i}");
+ *pat = Box::new(Pat::Ident(PatIdent {
+ ident: Ident::new(&name, Span::call_site().into()),
+ attrs: Vec::new(),
+ by_ref: None,
+ mutability: None,
+ subpat: None,
+ }));
+
+ let field = fields.iter();
+ let refute = quote! {
+ let #variant { #( #field ),*, .. } = #name else { panic!("incorrect variant passed to function argument {i}"); };
+ };
+
+ stmt.insert(0, syn::parse2::<Stmt>(refute).expect("syntax error"));
+ }
+ }
+
+ item.into_token_stream().into()
+}
--
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