sqlx/src/ty_match.rs

use std::marker::PhantomData;

// These types allow the `query!()` and friends to compare a given parameter's type to
// an expected parameter type even if the former is behind a reference or in `Option`.

// For query parameters, Postgres gives us a single type ID which we convert to an "expected" or
// preferred Rust type, but there can actually be several types that are compatible for a given type
// in input position. E.g. for an expected parameter of `String`, we want to accept `String`,
// `Option<String>`, `&str` and `Option<&str>`. And for the best compiler errors we don't just
// want an `IsCompatible` trait (at least not without `#[on_unimplemented]` which is unstable
// for the foreseeable future).

// We can do this by using autoref (for method calls, the compiler adds reference ops until
// it finds a matching impl) with impls that technically don't overlap as a hacky form of
// specialization (but this works only if all types are statically known, i.e. we're not in a
// generic context; this should suit 99% of use cases for the macros).

pub fn same_type<T>(_1: &T, _2: &T) {}

pub struct WrapSame<T, U>(PhantomData<T>, PhantomData<U>);

impl<T, U> WrapSame<T, U> {
    pub fn new(_arg: &U) -> Self {
        WrapSame(PhantomData, PhantomData)
    }
}

pub trait WrapSameExt: Sized {
    type Wrapped;

    fn wrap_same(self) -> Self::Wrapped {
        panic!("only for type resolution")
    }
}

impl<T, U> WrapSameExt for WrapSame<T, Option<U>> {
    type Wrapped = Option<T>;
}

impl<T, U> WrapSameExt for &'_ WrapSame<T, U> {
    type Wrapped = T;
}

pub struct MatchBorrow<T, U>(PhantomData<T>, PhantomData<U>);

impl<T, U> MatchBorrow<T, U> {
    pub fn new(t: T, _u: &U) -> (T, Self) {
        (t, MatchBorrow(PhantomData, PhantomData))
    }
}

pub trait MatchBorrowExt: Sized {
    type Matched;

    fn match_borrow(self) -> Self::Matched {
        panic!("only for type resolution")
    }
}

impl<'a> MatchBorrowExt for MatchBorrow<Option<&'a str>, Option<String>> {
    type Matched = Option<&'a str>;
}

impl<'a> MatchBorrowExt for MatchBorrow<Option<&'a [u8]>, Option<Vec<u8>>> {
    type Matched = Option<&'a [u8]>;
}

impl<'a> MatchBorrowExt for MatchBorrow<Option<&'a str>, Option<&'a String>> {
    type Matched = Option<&'a str>;
}

impl<'a> MatchBorrowExt for MatchBorrow<Option<&'a [u8]>, Option<&'a Vec<u8>>> {
    type Matched = Option<&'a [u8]>;
}

impl<'a> MatchBorrowExt for MatchBorrow<&'a str, String> {
    type Matched = &'a str;
}

impl<'a> MatchBorrowExt for MatchBorrow<&'a [u8], Vec<u8>> {
    type Matched = &'a [u8];
}

impl<T> MatchBorrowExt for MatchBorrow<&'_ T, T> {
    type Matched = T;
}

impl<T> MatchBorrowExt for MatchBorrow<&'_ &'_ T, T> {
    type Matched = T;
}

impl<T> MatchBorrowExt for MatchBorrow<T, &'_ T> {
    type Matched = T;
}

impl<T> MatchBorrowExt for MatchBorrow<T, &'_ &'_ T> {
    type Matched = T;
}

impl<T> MatchBorrowExt for MatchBorrow<Option<&'_ T>, Option<T>> {
    type Matched = Option<T>;
}

impl<T> MatchBorrowExt for MatchBorrow<Option<&'_ &'_ T>, Option<T>> {
    type Matched = Option<T>;
}

impl<T> MatchBorrowExt for MatchBorrow<Option<T>, Option<&'_ T>> {
    type Matched = Option<T>;
}

impl<T> MatchBorrowExt for MatchBorrow<Option<T>, Option<&'_ &'_ T>> {
    type Matched = Option<T>;
}

impl<T, U> MatchBorrowExt for &'_ MatchBorrow<T, U> {
    type Matched = U;
}

pub fn conjure_value<T>() -> T {
    panic!()
}

pub fn dupe_value<T>(_t: &T) -> T {
    panic!()
}

#[test]
fn test_dupe_value() {
    let ref val = (String::new(),);

    if false {
        let _: i32 = dupe_value(&0i32);
        let _: String = dupe_value(&String::new());
        let _: String = dupe_value(&val.0);
    }
}

#[test]
fn test_wrap_same() {
    if false {
        let _: i32 = WrapSame::<i32, _>::new(&0i32).wrap_same();
        let _: i32 = WrapSame::<i32, _>::new(&"hello, world!").wrap_same();
        let _: Option<i32> = WrapSame::<i32, _>::new(&Some(String::new())).wrap_same();
    }
}

#[test]
fn test_match_borrow() {
    if false {
        let (_, match_borrow) = MatchBorrow::new("", &String::new());
        let _: &str = match_borrow.match_borrow();

        let (_, match_borrow) = MatchBorrow::new(&&0i64, &0i64);
        let _: i64 = match_borrow.match_borrow();

        let (_, match_borrow) = MatchBorrow::new(&0i64, &0i64);
        let _: i64 = match_borrow.match_borrow();

        let (_, match_borrow) = MatchBorrow::new(0i64, &0i64);
        let _: i64 = match_borrow.match_borrow();
    }
}