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proc-macro の勉強して sqlx のバグを修正した話
2023-07-26 Rust、何もわからない... #9
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© 2023 estie Inc.
@southball02
SWE@estie
• ソフトウェアエンジニア(SWE)
• 京都大学工学部情報学科3年
• estieでは業務委託としてRustを使ったWebアプリの開
発に取り組んでいる
自己紹介
2
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© 2023 estie Inc.
今日やること
• マクロを触ってみる
• ざっと説明するので、気になる人はこのあとゆっくり読んでください
• 実際ライブラリの内部を見て、バグを修正してみる
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© 2023 estie Inc.
procedural macro?
• マクロの一種
• 抽象構文木（AST）から抽象構文木への変換を定義する
• 三種類ある：
• #[proc_macro] → println!("...")
• #[proc_macro_attribute] → #[test]
• #[proc_macro_derive] → #[derive(Clone)]
• 例えば sqlx は procedural macro でデータベースに接続して、クエリの型を確
認する
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© 2023 estie Inc.
© 2023 estie Inc.
初めてのproc_macro
1
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© 2023 estie Inc.
use proc_macro_test::print_twice;
#[test]
fn test() {
print_twice!("Hello, {}!", "world");
}
use proc_macro_test::print_twice;
#[test]
fn test() {
{
println!("Hello, {}!", "world");
println!("Hello, {}!", "world");
}
}
?
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© 2023 estie Inc.
# Cargo.toml
[package]
name = "proc-macro-test"
version = "0.1.0"
edition = "2021"
[lib]
proc-macro = true
[dependencies]
// lib.rs
use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree};
#[proc_macro]
pub fn print_twice(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
TokenTree::from(Group::new(
Delimiter::Brace,
vec![
vec![
TokenTree::from(Ident::new("println", Span::call_site())),
TokenTree::from(Punct::new('!', Spacing::Alone)),
TokenTree::from(Group::new(Delimiter::Parenthesis, input.clone())),
]
.into_iter()
.collect::(),
TokenTree::from(Punct::new(';', Spacing::Alone)).into(),
vec![
TokenTree::from(Ident::new("println", Span::call_site())),
TokenTree::from(Punct::new('!', Spacing::Alone)),
TokenTree::from(Group::new(Delimiter::Parenthesis, input.clone())),
]
.into_iter()
.collect::(),
]
.into_iter()
.collect::(),
))
.into()
}
＊あとでわかりやすい書き方説明するので
あんまり気にしなくて大丈夫です
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© 2023 estie Inc.
$ cargo +nightly test -- --nocapture
Compiling proc-macro-test v0.1.0 (/home/southball/proc-macro-test)
Finished test [unoptimized + debuginfo] target(s) in 0.15s
Running unittests src/lib.rs (target/debug/deps/proc_macro_test-03e1a98fcf1cb3da)
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
Running tests/test.rs (target/debug/deps/test-0863b971a4792ac0)
running 1 test
Hello, world!
Hello, world!
test test ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
Doc-tests proc-macro-test
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
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© 2023 estie Inc.
TokenStream とは？
TokenStream [
Literal {
kind: Str,
symbol: "Hello, {}!",
suffix: None,
span: #0 bytes(71..83),
},
Punct {
ch: ',',
spacing: Alone,
span: #0 bytes(83..84),
},
Literal {
kind: Str,
symbol: "world",
suffix: None,
span: #0 bytes(85..92),
},
]
use proc_macro_test::print_twice;
#[test]
fn test() {
print_twice!("Hello, {}!", "world");
}
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© 2023 estie Inc.
proc_macro2 + quote
#[proc_macro]
pub fn print_twice(input: proc_macro::TokenStream)
-> proc_macro::TokenStream {
let input = proc_macro2::TokenStream::from(input);
quote::quote! {
{
println!( #input );
println!( #input );
}
}
.into()
}
proc_macro2：
proc macro を定義する crate 以外で
proc_macro ライブラリの使うための crate
quote：
Rust を抽象構文木に変換する crate
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© 2023 estie Inc.
syn crate
AST 上に構文解析をして、Rust の ASTに変換するライブラリ
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© 2023 estie Inc.
syn crate：例
// test.rs
use proc_macro_test::print_rust_ast;
#[test]
fn test() {
print_rust_ast!(1 + 2 * 3);
}
Expr::Binary {
attrs: [],
left: Expr::Lit {
attrs: [],
lit: Lit::Int {
token: 1,
},
},
op: BinOp::Add(
Plus,
),
right: Expr::Binary {
attrs: [],
left: Expr::Lit {
attrs: [],
lit: Lit::Int {
token: 2,
},
},
op: BinOp::Mul(
Star,
),
right: Expr::Lit {
attrs: [],
lit: Lit::Int {
token: 3,
},
},
},
}
# cargo.toml
[package]
name = "proc-macro-test"
version = "0.1.0"
edition = "2021"
[lib]
proc-macro = true
[dependencies]
quote = "1.0"
proc-macro2 = "1.0“
syn = { version = "2.0", features =
["extra-traits"] }
// lib.rs
use proc_macro2::{Literal, TokenTree};
#[proc_macro]
pub fn print_rust_ast(input: proc_macro::TokenStream)
-> proc_macro::TokenStream {
let input = TokenTree::from(
Literal::string(&format!(
"{:#?}",
syn::parse_macro_input!(input as syn::Expr)
)
));
quote::quote! {
println!( "{}", #input );
}
.into()
}
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© 2023 estie Inc.
cargo expand
$ cargo expand --test test
Checking proc-macro-test v0.1.0 (/home/southball/proc-macro-test)
Finished dev [unoptimized + debuginfo] target(s) in 0.03s
...
fn test() {
{
{
::std::io::_print(format_args!("Hello, {0}!¥n", "world"));
};
{
::std::io::_print(format_args!("Hello, {0}!¥n", "world"));
};
};
}
#[rustc_main]
pub fn main() -> () {
extern crate test;
test::test_main_static(&[&test])
}
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© 2023 estie Inc.
© 2023 estie Inc.
sqlx のバグ修正の話
2
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© 2023 estie Inc.
use anyhow::Ok;
use sqlx::MySqlConnection;
// ...
struct Struct { a: i32 }
async fn handler(conn: &mut MySqlConnection) {
let data = sqlx::query_as!(Struct, "...")
.fetch_all(conn)
.await;
}
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© 2023 estie Inc.
error[E0308]: mismatched types
--> mod.rs:8:16
|
8 | let data = sqlx::query_as!(Struct, "...")
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `Result<_, Error>`, found `Result`
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© 2023 estie Inc.
???
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© 2023 estie Inc.
use anyhow::Ok;
use sqlx::MySqlConnection;
// ...
struct Struct {
a: i32
}
async fn handler() {
let data = {
{
#[allow(clippy::all)]
{
use ::sqlx::Arguments as _;
let query_args = ::Arguments::default();
::sqlx::query_with::("...", query_args)
.try_map(|row: sqlx::mysql::MySqlRow| {
use ::sqlx::Row as _;
let sqlx_query_as_a = row
.try_get_unchecked::(0usize)?;
Ok(Struct { a: sqlx_query_as_a })
})
}
}
}
.fetch_all(conn)
.await;
}
cargo-expand
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© 2023 estie Inc.
use anyhow::Ok;
use sqlx::MySqlConnection;
// ...
struct Struct {
a: i32
}
async fn handler() {
let data = {
{
#[allow(clippy::all)]
{
use ::sqlx::Arguments as _;
let query_args = ::Arguments::default();
::sqlx::query_with::("...", query_args)
.try_map(|row: sqlx::mysql::MySqlRow| {
use ::sqlx::Row as _;
let sqlx_query_as_a = row
.try_get_unchecked::(0usize)?;
Ok
(Struct { a: sqlx_query_as_a })
})
}
}
}
.fetch_all(conn)
.await;
}
cargo-expand
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© 2023 estie Inc.
THIS IS (NOT) OK
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© 2023 estie Inc.
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© 2023 estie Inc.
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© 2023 estie Inc.
proc-macro の勉強して sqlx のバグを修正した話 まとめ
• proc macro の基本の作り方の紹介をした
• proc_macro, proc_macro2 で抽象構文木上に操作する
• syn で Rust の構文解析する
• quote で Rust のコードを抽象構文木に変換する
• マクロの実装を見る
• cargo-expand でマクロを展開する
• 作ってみよう！