diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6936990
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+/target
+**/*.rs.bk
+Cargo.lock
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..fe51652
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,14 @@
+language: rust
+
+script:
+  - cargo test
+
+matrix:
+  include:
+    - rust: nightly
+    - rust: beta
+      env: RUSTFLAGS='--cfg remain_stable_testing'
+    - rust: stable
+      env: RUSTFLAGS='--cfg remain_stable_testing'
+    - rust: 1.31.0
+      env: RUSTFLAGS='--cfg remain_stable_testing'
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..c635f7a
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,22 @@
+[package]
+name = "remain"
+version = "0.1.3" # remember to update number in readme for major versions
+authors = ["David Tolnay <dtolnay@gmail.com>"]
+edition = "2018"
+license = "MIT OR Apache-2.0"
+description = "Compile-time checks that an enum, struct, or match is written in sorted order."
+repository = "https://github.com/dtolnay/remain"
+documentation = "https://docs.rs/remain"
+readme = "README.md"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "0.4"
+quote = "0.6"
+syn = { version = "0.15", features = ["full", "visit-mut"] }
+
+[dev-dependencies]
+select-rustc = "0.1"
+trybuild = "1.0"
diff --git a/LICENSE-APACHE b/LICENSE-APACHE
new file mode 100644
index 0000000..16fe87b
--- /dev/null
+++ b/LICENSE-APACHE
@@ -0,0 +1,201 @@
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diff --git a/LICENSE-MIT b/LICENSE-MIT
new file mode 100644
index 0000000..31aa793
--- /dev/null
+++ b/LICENSE-MIT
@@ -0,0 +1,23 @@
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
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+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..c3a4877
--- /dev/null
+++ b/README.md
@@ -0,0 +1,135 @@
+Remain sorted
+=============
+
+[![Build Status](https://api.travis-ci.com/dtolnay/remain.svg?branch=master)](https://travis-ci.com/dtolnay/remain)
+[![Latest Version](https://img.shields.io/crates/v/remain.svg)](https://crates.io/crates/remain)
+[![Rust Documentation](https://img.shields.io/badge/api-rustdoc-blue.svg)](https://docs.rs/remain)
+
+This crate provides an attribute macro to check at compile time that the
+variants of an enum or the arms of a match expression are written in sorted
+order.
+
+```toml
+[dependencies]
+remain = "0.1"
+```
+
+## Syntax
+
+Place a `#[remain::sorted]` attribute on enums, structs, match-expressions, or
+let-statements whose value is a match-expression.
+
+Alternatively, import as `use remain::sorted;` and use `#[sorted]` as the
+attribute.
+
+```rust
+#[remain::sorted]
+#[derive(Debug)]
+pub enum Error {
+    BlockSignal(signal::Error),
+    CreateCrasClient(libcras::Error),
+    CreateEventFd(sys_util::Error),
+    CreateSignalFd(sys_util::SignalFdError),
+    CreateSocket(io::Error),
+    DetectImageType(qcow::Error),
+    DeviceJail(io_jail::Error),
+    NetDeviceNew(virtio::NetError),
+    SpawnVcpu(io::Error),
+}
+
+#[remain::sorted]
+#[derive(Debug)]
+pub enum Registers {
+    ax: u16,
+    cx: u16,
+    di: u16,
+    si: u16,
+    sp: u16,
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use self::Error::*;
+
+        #[remain::sorted]
+        match self {
+            BlockSignal(e) => write!(f, "failed to block signal: {}", e),
+            CreateCrasClient(e) => write!(f, "failed to create cras client: {}", e),
+            CreateEventFd(e) => write!(f, "failed to create eventfd: {}", e),
+            CreateSignalFd(e) => write!(f, "failed to create signalfd: {}", e),
+            CreateSocket(e) => write!(f, "failed to create socket: {}", e),
+            DetectImageType(e) => write!(f, "failed to detect disk image type: {}", e),
+            DeviceJail(e) => write!(f, "failed to jail device: {}", e),
+            NetDeviceNew(e) => write!(f, "failed to set up virtio networking: {}", e),
+            SpawnVcpu(e) => write!(f, "failed to spawn VCPU thread: {}", e),
+        }
+    }
+}
+```
+
+If an enum variant, struct field, or match arm is inserted out of order,
+
+```diff
+      NetDeviceNew(virtio::NetError),
+      SpawnVcpu(io::Error),
++     AaaUhOh(Box<dyn StdError>),
+  }
+```
+
+then the macro produces a compile error.
+
+```console
+error: AaaUhOh should sort before BlockSignal
+  --> tests/stable.rs:49:5
+   |
+49 |     AaaUhOh(Box<dyn StdError>),
+   |     ^^^^^^^
+```
+
+## Compiler support
+
+The attribute on enums and structs is supported on any rustc version 1.31+.
+
+Rust does not yet have stable support for user-defined attributes within a
+function body, so the attribute on match-expressions and let-statements requires
+a nightly compiler and the following two features enabled:
+
+```rust
+#![feature(proc_macro_hygiene, stmt_expr_attributes)]
+```
+
+As a stable alternative, this crate provides a function-level attribute called
+`#[remain::check]` which makes match-expression and let-statement attributes
+work on any rustc version 1.31+. Place this attribute on any function containing
+`#[sorted]` to make them work on a stable compiler.
+
+```rust
+impl Display for Error {
+    #[remain::check]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use self::Error::*;
+
+        #[sorted]
+        match self {
+            /* ... */
+        }
+    }
+}
+```
+
+<br>
+
+#### License
+
+<sup>
+Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
+2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
+</sup>
+
+<br>
+
+<sub>
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
+be dual licensed as above, without any additional terms or conditions.
+</sub>
diff --git a/src/check.rs b/src/check.rs
new file mode 100644
index 0000000..0995078
--- /dev/null
+++ b/src/check.rs
@@ -0,0 +1,83 @@
+use syn::{Arm, Ident, Result, Variant};
+use syn::{Error, Field, Pat, PatIdent};
+
+use crate::compare::Path;
+use crate::format;
+use crate::parse::Input::{self, *};
+
+pub fn sorted(input: Input) -> Result<()> {
+    let paths = match input {
+        Enum(item) => collect_paths(item.variants)?,
+        Struct(fields) => collect_paths(fields.named)?,
+        Match(expr) | Let(expr) => collect_paths(expr.arms)?,
+    };
+
+    for i in 1..paths.len() {
+        let cur = &paths[i];
+        if *cur < paths[i - 1] {
+            let lesser = cur;
+            let correct_pos = paths[..i - 1].binary_search(cur).unwrap_err();
+            let greater = &paths[correct_pos];
+            return Err(format::error(lesser, greater));
+        }
+    }
+
+    Ok(())
+}
+
+fn collect_paths<I>(iter: I) -> Result<Vec<Path>>
+where
+    I: IntoIterator,
+    I::Item: IntoPath,
+{
+    iter.into_iter().map(IntoPath::into_path).collect()
+}
+
+trait IntoPath {
+    fn into_path(self) -> Result<Path>;
+}
+
+impl IntoPath for Variant {
+    fn into_path(self) -> Result<Path> {
+        Ok(Path {
+            segments: vec![self.ident],
+        })
+    }
+}
+
+impl IntoPath for Field {
+    fn into_path(self) -> Result<Path> {
+        Ok(Path {
+            segments: vec![self.ident.expect("must be named field")],
+        })
+    }
+}
+
+impl IntoPath for Arm {
+    fn into_path(self) -> Result<Path> {
+        // Sort by just the first pat.
+        let pat = self.pats.into_iter().next().expect("at least one pat");
+
+        let segments = match pat {
+            Pat::Wild(pat) => vec![Ident::from(pat.underscore_token)],
+            Pat::Path(pat) => idents_of_path(pat.path),
+            Pat::Struct(pat) => idents_of_path(pat.path),
+            Pat::TupleStruct(pat) => idents_of_path(pat.path),
+            Pat::Ident(ref pat) if is_just_ident(pat) => vec![pat.ident.clone()],
+            other => {
+                let msg = "unsupported by #[remain::sorted]";
+                return Err(Error::new_spanned(other, msg));
+            }
+        };
+
+        Ok(Path { segments })
+    }
+}
+
+fn idents_of_path(path: syn::Path) -> Vec<Ident> {
+    path.segments.into_iter().map(|seg| seg.ident).collect()
+}
+
+fn is_just_ident(pat: &PatIdent) -> bool {
+    pat.by_ref.is_none() && pat.mutability.is_none() && pat.subpat.is_none()
+}
diff --git a/src/compare.rs b/src/compare.rs
new file mode 100644
index 0000000..59f997d
--- /dev/null
+++ b/src/compare.rs
@@ -0,0 +1,45 @@
+use proc_macro2::Ident;
+use std::cmp::Ordering;
+
+#[derive(PartialEq, Eq)]
+pub struct Path {
+    pub segments: Vec<Ident>,
+}
+
+impl PartialOrd for Path {
+    fn partial_cmp(&self, other: &Path) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Path {
+    fn cmp(&self, other: &Path) -> Ordering {
+        // Lexicographic ordering across path segments.
+        for (lhs, rhs) in self.segments.iter().zip(&other.segments) {
+            match cmp(&lhs.to_string(), &rhs.to_string()) {
+                Ordering::Equal => {}
+                non_eq => return non_eq,
+            }
+        }
+
+        self.segments.len().cmp(&other.segments.len())
+    }
+}
+
+// TODO: more intelligent comparison
+// for example to handle numeric cases like E9 < E10.
+fn cmp(lhs: &str, rhs: &str) -> Ordering {
+    // Sort `_` last.
+    match (lhs == "_", rhs == "_") {
+        (true, true) => return Ordering::Equal,
+        (true, false) => return Ordering::Greater,
+        (false, true) => return Ordering::Less,
+        (false, false) => {}
+    }
+
+    let lhs = lhs.to_ascii_lowercase();
+    let rhs = rhs.to_ascii_lowercase();
+
+    // For now: asciibetical ordering.
+    lhs.cmp(&rhs)
+}
diff --git a/src/emit.rs b/src/emit.rs
new file mode 100644
index 0000000..d1ddda8
--- /dev/null
+++ b/src/emit.rs
@@ -0,0 +1,39 @@
+use proc_macro::TokenStream;
+use proc_macro2::Span;
+use quote::quote;
+use syn::Error;
+
+#[derive(Copy, Clone)]
+pub enum Kind {
+    Enum,
+    Match,
+    Struct,
+    Let,
+}
+
+pub fn emit(err: Error, kind: Kind, original: TokenStream) -> TokenStream {
+    let mut err = err;
+    if !probably_has_spans(kind) {
+        // Otherwise the error is printed without any line number.
+        err = Error::new(Span::call_site(), &err.to_string());
+    }
+
+    let err = err.to_compile_error();
+    let original = proc_macro2::TokenStream::from(original);
+
+    let expanded = match kind {
+        Kind::Enum | Kind::Let | Kind::Struct => quote!(#err #original),
+        Kind::Match => quote!({ #err #original }),
+    };
+
+    TokenStream::from(expanded)
+}
+
+// Rustc is so bad at spans.
+// https://github.com/rust-lang/rust/issues/43081
+fn probably_has_spans(kind: Kind) -> bool {
+    match kind {
+        Kind::Enum | Kind::Struct => true,
+        Kind::Match | Kind::Let => false,
+    }
+}
diff --git a/src/format.rs b/src/format.rs
new file mode 100644
index 0000000..5832643
--- /dev/null
+++ b/src/format.rs
@@ -0,0 +1,27 @@
+use proc_macro2::TokenStream;
+use quote::TokenStreamExt;
+use std::fmt::{self, Display};
+use syn::Error;
+
+use crate::compare::Path;
+
+impl Display for Path {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        for (i, segment) in self.segments.iter().enumerate() {
+            if i > 0 {
+                formatter.write_str("::")?;
+            }
+            segment.fmt(formatter)?;
+        }
+        Ok(())
+    }
+}
+
+pub fn error(lesser: &Path, greater: &Path) -> Error {
+    let mut spans = TokenStream::new();
+    spans.append_all(&lesser.segments);
+
+    let msg = format!("{} should sort before {}", lesser, greater);
+
+    Error::new_spanned(spans, msg)
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..967143e
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,176 @@
+//! This crate provides an attribute macro to check at compile time that the
+//! variants of an enum or the arms of a match expression are written in sorted
+//! order.
+//!
+//! # Syntax
+//!
+//! Place a `#[remain::sorted]` attribute on enums, structs, match-expressions,
+//! or let-statements whose value is a match-expression.
+//!
+//! Alternatively, import as `use remain::sorted;` and use `#[sorted]` as the
+//! attribute.
+//!
+//! ```
+//! # use std::error::Error as StdError;
+//! # use std::fmt::{self, Display};
+//! # use std::io;
+//! #
+//! #[remain::sorted]
+//! #[derive(Debug)]
+//! pub enum Error {
+//!     BlockSignal(signal::Error),
+//!     CreateCrasClient(libcras::Error),
+//!     CreateEventFd(sys_util::Error),
+//!     CreateSignalFd(sys_util::SignalFdError),
+//!     CreateSocket(io::Error),
+//!     DetectImageType(qcow::Error),
+//!     DeviceJail(io_jail::Error),
+//!     NetDeviceNew(virtio::NetError),
+//!     SpawnVcpu(io::Error),
+//! }
+//!
+//! impl Display for Error {
+//!     # #[remain::check]
+//!     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+//!         use self::Error::*;
+//!
+//!         #[remain::sorted]
+//!         match self {
+//!             BlockSignal(e) => write!(f, "failed to block signal: {}", e),
+//!             CreateCrasClient(e) => write!(f, "failed to create cras client: {}", e),
+//!             CreateEventFd(e) => write!(f, "failed to create eventfd: {}", e),
+//!             CreateSignalFd(e) => write!(f, "failed to create signalfd: {}", e),
+//!             CreateSocket(e) => write!(f, "failed to create socket: {}", e),
+//!             DetectImageType(e) => write!(f, "failed to detect disk image type: {}", e),
+//!             DeviceJail(e) => write!(f, "failed to jail device: {}", e),
+//!             NetDeviceNew(e) => write!(f, "failed to set up virtio networking: {}", e),
+//!             SpawnVcpu(e) => write!(f, "failed to spawn VCPU thread: {}", e),
+//!         }
+//!     }
+//! }
+//! #
+//! # mod signal {
+//! #     pub use std::io::Error;
+//! # }
+//! #
+//! # mod libcras {
+//! #     pub use std::io::Error;
+//! # }
+//! #
+//! # mod sys_util {
+//! #     pub use std::io::{Error, Error as SignalFdError};
+//! # }
+//! #
+//! # mod qcow {
+//! #     pub use std::io::Error;
+//! # }
+//! #
+//! # mod io_jail {
+//! #     pub use std::io::Error;
+//! # }
+//! #
+//! # mod virtio {
+//! #     pub use std::io::Error as NetError;
+//! # }
+//! #
+//! # fn main() {}
+//! ```
+//!
+//! If an enum variant, struct field, or match arm is inserted out of order,\
+//!
+//! ```diff
+//!       NetDeviceNew(virtio::NetError),
+//!       SpawnVcpu(io::Error),
+//! +     AaaUhOh(Box<dyn StdError>),
+//!   }
+//! ```
+//!
+//! then the macro produces a compile error.
+//!
+//! ```console
+//! error: AaaUhOh should sort before BlockSignal
+//!   --> tests/stable.rs:49:5
+//!    |
+//! 49 |     AaaUhOh(Box<dyn StdError>),
+//!    |     ^^^^^^^
+//! ```
+//!
+//! # Compiler support
+//!
+//! The attribute on enums is supported on any rustc version 1.31+.
+//!
+//! Rust does not yet have stable support for user-defined attributes within a
+//! function body, so the attribute on match-expressions and let-statements
+//! requires a nightly compiler and the following two features enabled:
+//!
+//! ```
+//! # const IGNORE: &str = stringify! {
+//! #![feature(proc_macro_hygiene, stmt_expr_attributes)]
+//! # };
+//! ```
+//!
+//! As a stable alternative, this crate provides a function-level attribute
+//! called `#[remain::check]` which makes match-expression and let-statement
+//! attributes work on any rustc version 1.31+. Place this attribute on any
+//! function containing `#[sorted]` to make them work on a stable compiler.
+//!
+//! ```
+//! # use std::fmt::{self, Display};
+//! #
+//! # enum Error {}
+//! #
+//! impl Display for Error {
+//!     #[remain::check]
+//!     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+//!         use self::Error::*;
+//!
+//!         #[sorted]
+//!         match self {
+//!             /* ... */
+//!             # _ => unimplemented!(),
+//!         }
+//!     }
+//! }
+//! #
+//! # fn main() {}
+//! ```
+
+extern crate proc_macro;
+
+mod check;
+mod compare;
+mod emit;
+mod format;
+mod parse;
+mod visit;
+
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, ItemFn};
+
+use crate::emit::emit;
+use crate::parse::{Input, Nothing};
+
+#[proc_macro_attribute]
+pub fn sorted(args: TokenStream, input: TokenStream) -> TokenStream {
+    let original = input.clone();
+
+    let _ = parse_macro_input!(args as Nothing);
+    let input = parse_macro_input!(input as Input);
+    let kind = input.kind();
+
+    match check::sorted(input) {
+        Ok(()) => original,
+        Err(err) => emit(err, kind, original),
+    }
+}
+
+#[proc_macro_attribute]
+pub fn check(args: TokenStream, input: TokenStream) -> TokenStream {
+    let _ = parse_macro_input!(args as Nothing);
+    let mut input = parse_macro_input!(input as ItemFn);
+
+    visit::check(&mut input);
+
+    TokenStream::from(quote!(#input))
+}
diff --git a/src/parse.rs b/src/parse.rs
new file mode 100644
index 0000000..97bd9f8
--- /dev/null
+++ b/src/parse.rs
@@ -0,0 +1,80 @@
+use proc_macro2::Span;
+use syn::parse::{Parse, ParseStream};
+use syn::{Attribute, Error, Expr, Fields, Result, Stmt, Token, Visibility};
+
+use crate::emit::Kind;
+
+pub struct Nothing;
+
+impl Parse for Nothing {
+    fn parse(_input: ParseStream) -> Result<Self> {
+        Ok(Nothing)
+    }
+}
+
+pub enum Input {
+    Enum(syn::ItemEnum),
+    Match(syn::ExprMatch),
+    Struct(syn::FieldsNamed),
+    Let(syn::ExprMatch),
+}
+
+impl Input {
+    pub fn kind(&self) -> Kind {
+        match self {
+            Input::Enum(_) => Kind::Enum,
+            Input::Match(_) => Kind::Match,
+            Input::Struct(_) => Kind::Struct,
+            Input::Let(_) => Kind::Let,
+        }
+    }
+}
+
+impl Parse for Input {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let _ = input.call(Attribute::parse_outer)?;
+
+        if input.peek(Token![match]) {
+            let expr = match input.parse()? {
+                Expr::Match(expr) => expr,
+                _ => unreachable!("expected match"),
+            };
+            return Ok(Input::Match(expr));
+        }
+
+        if input.peek(Token![let]) {
+            let stmt = match input.parse()? {
+                Stmt::Local(stmt) => stmt,
+                _ => unreachable!("expected let"),
+            };
+            let init = match stmt.init {
+                Some((_, init)) => *init,
+                None => return Err(unexpected()),
+            };
+            let expr = match init {
+                Expr::Match(expr) => expr,
+                _ => return Err(unexpected()),
+            };
+            return Ok(Input::Let(expr));
+        }
+
+        let ahead = input.fork();
+        let _: Visibility = ahead.parse()?;
+        if ahead.peek(Token![enum]) {
+            return input.parse().map(Input::Enum);
+        } else if ahead.peek(Token![struct]) {
+            let input: syn::ItemStruct = input.parse()?;
+            if let Fields::Named(fields) = input.fields {
+                return Ok(Input::Struct(fields));
+            }
+        }
+
+        Err(unexpected())
+    }
+}
+
+fn unexpected() -> Error {
+    let span = Span::call_site();
+    let msg = "expected enum, struct, or match expression";
+    Error::new(span, msg)
+}
diff --git a/src/visit.rs b/src/visit.rs
new file mode 100644
index 0000000..f681aa9
--- /dev/null
+++ b/src/visit.rs
@@ -0,0 +1,77 @@
+use quote::quote;
+use syn::visit_mut::{self, VisitMut};
+use syn::{parse_quote, Attribute, Expr, ExprMatch, ItemFn, Local};
+
+use crate::parse::Input;
+
+pub fn check(input: &mut ItemFn) {
+    Checker.visit_item_fn_mut(input);
+}
+
+struct Checker;
+
+impl VisitMut for Checker {
+    fn visit_expr_mut(&mut self, expr: &mut Expr) {
+        visit_mut::visit_expr_mut(self, expr);
+
+        let expr_match = match expr {
+            Expr::Match(expr) => expr,
+            _ => return,
+        };
+
+        if !take_sorted_attr(&mut expr_match.attrs) {
+            return;
+        }
+
+        let input = expr_match.clone();
+        check_and_insert_error(input, expr);
+    }
+
+    fn visit_local_mut(&mut self, local: &mut Local) {
+        visit_mut::visit_local_mut(self, local);
+
+        let init = match &local.init {
+            Some((_, init)) => init,
+            None => return,
+        };
+
+        let expr_match = match init.as_ref() {
+            Expr::Match(expr) => expr,
+            _ => return,
+        };
+
+        if !take_sorted_attr(&mut local.attrs) {
+            return;
+        }
+
+        let input = expr_match.clone();
+        let expr = local.init.as_mut().unwrap().1.as_mut();
+        check_and_insert_error(input, expr);
+    }
+}
+
+fn take_sorted_attr(attrs: &mut Vec<Attribute>) -> bool {
+    for i in 0..attrs.len() {
+        let path = &attrs[i].path;
+        let path = quote!(#path).to_string();
+        if path == "sorted" || path == "remain :: sorted" {
+            attrs.remove(i);
+            return true;
+        }
+    }
+
+    false
+}
+
+fn check_and_insert_error(input: ExprMatch, out: &mut Expr) {
+    let original = quote!(#input);
+    let input = Input::Match(input);
+
+    if let Err(err) = crate::check::sorted(input) {
+        let err = err.to_compile_error();
+        *out = parse_quote!({
+            #err
+            #original
+        });
+    }
+}
diff --git a/tests/compiletest.rs b/tests/compiletest.rs
new file mode 100644
index 0000000..2e861bf
--- /dev/null
+++ b/tests/compiletest.rs
@@ -0,0 +1,6 @@
+#[rustc::attr(not(nightly), ignore)]
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/ui/*.rs");
+}
diff --git a/tests/stable.rs b/tests/stable.rs
new file mode 100644
index 0000000..a3b6a7b
--- /dev/null
+++ b/tests/stable.rs
@@ -0,0 +1,45 @@
+#![allow(dead_code)]
+
+#[remain::sorted]
+pub enum TestEnum {
+    A,
+    B,
+    C,
+    D,
+}
+
+#[remain::sorted]
+pub struct TestStruct {
+    a: usize,
+    b: usize,
+    c: usize,
+    d: usize,
+}
+
+#[test]
+#[remain::check]
+fn test_match() {
+    let value = TestEnum::A;
+
+    #[sorted]
+    let _ = match value {
+        TestEnum::A => {}
+        TestEnum::B => {}
+        TestEnum::C => {}
+        _ => {}
+    };
+}
+
+#[test]
+#[remain::check]
+fn test_let() {
+    let value = TestEnum::A;
+
+    #[sorted]
+    match value {
+        TestEnum::A => {}
+        TestEnum::B => {}
+        TestEnum::C => {}
+        _ => {}
+    }
+}
diff --git a/tests/ui/enum.rs b/tests/ui/enum.rs
new file mode 100644
index 0000000..dc98475
--- /dev/null
+++ b/tests/ui/enum.rs
@@ -0,0 +1,11 @@
+use remain::sorted;
+
+#[sorted]
+enum E {
+    Aaa,
+    Ccc(u8),
+    Ddd { u: u8 },
+    Bbb(u8, u8),
+}
+
+fn main() {}
diff --git a/tests/ui/enum.stderr b/tests/ui/enum.stderr
new file mode 100644
index 0000000..50ffa8c
--- /dev/null
+++ b/tests/ui/enum.stderr
@@ -0,0 +1,5 @@
+error: Bbb should sort before Ccc
+ --> $DIR/enum.rs:8:5
+  |
+8 |     Bbb(u8, u8),
+  |     ^^^
diff --git a/tests/ui/let-stable.rs b/tests/ui/let-stable.rs
new file mode 100644
index 0000000..b05d3e3
--- /dev/null
+++ b/tests/ui/let-stable.rs
@@ -0,0 +1,19 @@
+enum E {
+    Aaa,
+    Bbb(u8, u8),
+    Ccc(u8),
+    Ddd { u: u8 },
+}
+
+#[remain::check]
+fn main() {
+    let value = E::Aaa;
+
+    #[sorted]
+    let _ = match value {
+        E::Aaa => {}
+        E::Ccc(_) => {}
+        E::Ddd { u: _ } => {}
+        E::Bbb(_, _) => {}
+    };
+}
diff --git a/tests/ui/let-stable.stderr b/tests/ui/let-stable.stderr
new file mode 100644
index 0000000..9073750
--- /dev/null
+++ b/tests/ui/let-stable.stderr
@@ -0,0 +1,5 @@
+error: E::Bbb should sort before E::Ccc
+  --> $DIR/let-stable.rs:17:9
+   |
+17 |         E::Bbb(_, _) => {}
+   |         ^^^^^^
diff --git a/tests/ui/let-unstable.rs b/tests/ui/let-unstable.rs
new file mode 100644
index 0000000..8d65c52
--- /dev/null
+++ b/tests/ui/let-unstable.rs
@@ -0,0 +1,22 @@
+#![feature(proc_macro_hygiene, stmt_expr_attributes)]
+
+use remain::sorted;
+
+enum E {
+    Aaa,
+    Bbb(u8, u8),
+    Ccc(u8),
+    Ddd { u: u8 },
+}
+
+fn main() {
+    let value = E::Aaa;
+
+    #[sorted]
+    let _ = match value {
+        E::Aaa => {}
+        E::Ccc(_) => {}
+        E::Ddd { u: _ } => {}
+        E::Bbb(_, _) => {}
+    };
+}
diff --git a/tests/ui/let-unstable.stderr b/tests/ui/let-unstable.stderr
new file mode 100644
index 0000000..97c5ba1
--- /dev/null
+++ b/tests/ui/let-unstable.stderr
@@ -0,0 +1,5 @@
+error: E::Bbb should sort before E::Ccc
+  --> $DIR/let-unstable.rs:15:5
+   |
+15 |     #[sorted]
+   |     ^^^^^^^^^
diff --git a/tests/ui/match-stable.rs b/tests/ui/match-stable.rs
new file mode 100644
index 0000000..6bdade4
--- /dev/null
+++ b/tests/ui/match-stable.rs
@@ -0,0 +1,19 @@
+enum E {
+    Aaa,
+    Bbb(u8, u8),
+    Ccc(u8),
+    Ddd { u: u8 },
+}
+
+#[remain::check]
+fn main() {
+    let value = E::Aaa;
+
+    #[sorted]
+    match value {
+        E::Aaa => {}
+        E::Ccc(_) => {}
+        E::Ddd { u: _ } => {}
+        E::Bbb(_, _) => {}
+    }
+}
diff --git a/tests/ui/match-stable.stderr b/tests/ui/match-stable.stderr
new file mode 100644
index 0000000..183daa9
--- /dev/null
+++ b/tests/ui/match-stable.stderr
@@ -0,0 +1,5 @@
+error: E::Bbb should sort before E::Ccc
+  --> $DIR/match-stable.rs:17:9
+   |
+17 |         E::Bbb(_, _) => {}
+   |         ^^^^^^
diff --git a/tests/ui/match-unstable.rs b/tests/ui/match-unstable.rs
new file mode 100644
index 0000000..db047f1
--- /dev/null
+++ b/tests/ui/match-unstable.rs
@@ -0,0 +1,22 @@
+#![feature(proc_macro_hygiene, stmt_expr_attributes)]
+
+use remain::sorted;
+
+enum E {
+    Aaa,
+    Bbb(u8, u8),
+    Ccc(u8),
+    Ddd { u: u8 },
+}
+
+fn main() {
+    let value = E::Aaa;
+
+    #[sorted]
+    match value {
+        E::Aaa => {}
+        E::Ccc(_) => {}
+        E::Ddd { u: _ } => {}
+        E::Bbb(_, _) => {}
+    }
+}
diff --git a/tests/ui/match-unstable.stderr b/tests/ui/match-unstable.stderr
new file mode 100644
index 0000000..b2bdea0
--- /dev/null
+++ b/tests/ui/match-unstable.stderr
@@ -0,0 +1,5 @@
+error: E::Bbb should sort before E::Ccc
+  --> $DIR/match-unstable.rs:15:5
+   |
+15 |     #[sorted]
+   |     ^^^^^^^^^
diff --git a/tests/ui/struct.rs b/tests/ui/struct.rs
new file mode 100644
index 0000000..5f2cd41
--- /dev/null
+++ b/tests/ui/struct.rs
@@ -0,0 +1,11 @@
+use remain::sorted;
+
+#[sorted]
+struct TestStruct {
+    d: usize,
+    c: usize,
+    a: usize,
+    b: usize,
+}
+
+fn main() {}
diff --git a/tests/ui/struct.stderr b/tests/ui/struct.stderr
new file mode 100644
index 0000000..2ead15b
--- /dev/null
+++ b/tests/ui/struct.stderr
@@ -0,0 +1,5 @@
+error: c should sort before d
+ --> $DIR/struct.rs:6:5
+  |
+6 |     c: usize,
+  |     ^
diff --git a/tests/ui/unnamed-fields.rs b/tests/ui/unnamed-fields.rs
new file mode 100644
index 0000000..2fcfda9
--- /dev/null
+++ b/tests/ui/unnamed-fields.rs
@@ -0,0 +1,7 @@
+#[remain::sorted]
+struct TupleStruct(usize, usize, usize);
+
+#[remain::sorted]
+struct UnitStruct;
+
+fn main() {}
diff --git a/tests/ui/unnamed-fields.stderr b/tests/ui/unnamed-fields.stderr
new file mode 100644
index 0000000..b7e28f5
--- /dev/null
+++ b/tests/ui/unnamed-fields.stderr
@@ -0,0 +1,11 @@
+error: expected enum, struct, or match expression
+ --> $DIR/unnamed-fields.rs:1:1
+  |
+1 | #[remain::sorted]
+  | ^^^^^^^^^^^^^^^^^
+
+error: expected enum, struct, or match expression
+ --> $DIR/unnamed-fields.rs:4:1
+  |
+4 | #[remain::sorted]
+  | ^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/unsupported.rs b/tests/ui/unsupported.rs
new file mode 100644
index 0000000..b11c974
--- /dev/null
+++ b/tests/ui/unsupported.rs
@@ -0,0 +1,10 @@
+#[remain::check]
+fn main() {
+    let value = 0;
+
+    #[sorted]
+    match value {
+        0..=20 => {}
+        _ => {}
+    }
+}
diff --git a/tests/ui/unsupported.stderr b/tests/ui/unsupported.stderr
new file mode 100644
index 0000000..e471e1e
--- /dev/null
+++ b/tests/ui/unsupported.stderr
@@ -0,0 +1,5 @@
+error: unsupported by #[remain::sorted]
+ --> $DIR/unsupported.rs:7:9
+  |
+7 |         0..=20 => {}
+  |         ^^^^^^
diff --git a/tests/unstable.rs b/tests/unstable.rs
new file mode 100644
index 0000000..78dbd08
--- /dev/null
+++ b/tests/unstable.rs
@@ -0,0 +1,45 @@
+#![allow(dead_code)]
+#![cfg(not(remain_stable_testing))]
+#![feature(proc_macro_hygiene, stmt_expr_attributes)]
+
+#[remain::sorted]
+pub enum TestEnum {
+    A,
+    B,
+    C,
+    D,
+}
+
+#[remain::sorted]
+pub struct TestStruct {
+    a: usize,
+    b: usize,
+    c: usize,
+    d: usize,
+}
+
+#[test]
+fn test_match() {
+    let value = TestEnum::A;
+
+    #[remain::sorted]
+    let _ = match value {
+        TestEnum::A => {}
+        TestEnum::B => {}
+        TestEnum::C => {}
+        _ => {}
+    };
+}
+
+#[test]
+fn test_let() {
+    let value = TestEnum::A;
+
+    #[remain::sorted]
+    match value {
+        TestEnum::A => {}
+        TestEnum::B => {}
+        TestEnum::C => {}
+        _ => {}
+    }
+}