1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83

use crate::mlir_sys::{mlirStringRefCreateFromCString, mlirStringRefEqual, MlirStringRef};
use dashmap::DashMap;
use once_cell::sync::Lazy;
use std::{
    ffi::CString,
    marker::PhantomData,
    slice,
    str::{self, Utf8Error},
};

// We need to pass null-terminated strings to functions in the MLIR API although
// Rust's strings are not.
static STRING_CACHE: Lazy<DashMap<String, CString>> = Lazy::new(Default::default);

/// A string reference.
// https://mlir.llvm.org/docs/CAPI/#stringref
//
// TODO The documentation says string refs do not have to be null-terminated.
// But it looks like some functions do not handle strings not null-terminated?
#[derive(Clone, Copy, Debug)]
pub struct StringRef<'a> {
    raw: MlirStringRef,
    _parent: PhantomData<&'a ()>,
}

impl<'a> StringRef<'a> {
    /// Converts a string reference into a `str`.
    pub fn as_str(&self) -> Result<&str, Utf8Error> {
        unsafe {
            let bytes = slice::from_raw_parts(self.raw.data as *mut u8, self.raw.length);

            str::from_utf8(if bytes[bytes.len() - 1] == 0 {
                &bytes[..bytes.len() - 1]
            } else {
                bytes
            })
        }
    }

    pub(crate) const unsafe fn to_raw(self) -> MlirStringRef {
        self.raw
    }

    pub(crate) unsafe fn from_raw(string: MlirStringRef) -> Self {
        Self {
            raw: string,
            _parent: Default::default(),
        }
    }
}

impl<'a> PartialEq for StringRef<'a> {
    fn eq(&self, other: &Self) -> bool {
        unsafe { mlirStringRefEqual(self.raw, other.raw) }
    }
}

impl<'a> Eq for StringRef<'a> {}

#[allow(clippy::fallible_impl_from)] // TODO: rework this
impl From<&str> for StringRef<'static> {
    fn from(string: &str) -> Self {
        let entry = STRING_CACHE
            .entry(string.to_owned())
            .or_insert_with(|| CString::new(string).unwrap());
        unsafe { Self::from_raw(mlirStringRefCreateFromCString(entry.as_ptr())) }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn equal() {
        assert_eq!(StringRef::from("foo"), StringRef::from("foo"));
    }

    #[test]
    fn not_equal() {
        assert_ne!(StringRef::from("foo"), StringRef::from("bar"));
    }
}