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
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134

//! # `reflexive`
//!
//! A magical _meta_ function that evaluate (at compile-time if used inside a
//! macro which is the point of taking a `TokenStream` input) any Rust expr!
//!
//! ## Example
//!
//! ```rust
//! use reflexive::Sandbox;
//! use quote::quote;
//!
//! let test = Sandbox::new("calc").unwrap();
//! let x: u32 = test.eval(quote! { 2 + 2 }).unwrap();
//! assert!(x == 4);
//! ```
//!
//! This library indeed is not what would benefit the most your crate build
//! time, but it was still design in mind with the will of caching sandbox
//! compilation.
//!
//! ## Acknowledgments
//!
//! ⚠️ This is still a working experiment, not yet production ready.
//!
//! This project was part of a work assignment as an
//! [IOG](https://github.com/input-output-hk) contractor.
//!
//! ## License
//!
//! Licensed under either of [Apache License](LICENSE-APACHE), Version 2.0 or
//! [MIT license](LICENSE-MIT) at your option.
//!
//! Unless you explicitly state otherwise, any contribution intentionally submitted
//! for inclusion in this project by you, as defined in the Apache-2.0 license,
//! shall be dual licensed as above, without any additional terms or conditions.

#![forbid(unsafe_code)]

use proc_macro2::TokenStream;
use quote::quote;
use std::io::{Result, Write};
use std::path::PathBuf;
use std::process::Command;
use std::str::FromStr;
use std::sync::Mutex;
use std::{env, fs, io};

/// Internal representation of a `Sandbox`
///
/// A `Sandbox` is a throwable Cargo project made to evaluate arbitrary Rust
/// expression.
#[non_exhaustive]
pub struct Sandbox {
    lock: Mutex<()>,
    root_dir: PathBuf,
}

impl Sandbox {
    /// Create a `Sandbox` in `$OUT_DIR` folder
    ///
    /// `$OUT_DIR` is set by Cargo when `build.rs` is present :)
    pub fn new(uuid: &str) -> Result<Self> {
        let out_dir = env!("OUT_DIR");
        let mut root_dir = PathBuf::from(out_dir);
        root_dir.push(uuid);
        Command::new("mkdir")
            .args(["-p", root_dir.to_str().unwrap()])
            .output()?;
        Command::new("cargo")
            .current_dir(&root_dir)
            .args(["new", "sandbox"])
            .args(["--vcs", "none"])
            .output()?;

        // add [workspace] in Cargo.toml if not present
        let mut cargo_toml_path = root_dir.clone();
        cargo_toml_path.push("sandbox/Cargo.toml");
        if !fs::read_to_string(&cargo_toml_path)?.contains("[workspace]") {
            fs::OpenOptions::new()
                .append(true)
                .open(cargo_toml_path)?
                .write_all(b"\n[workspace]\n")?;
        }

        root_dir.push("sandbox");
        Ok(Sandbox {
            root_dir,
            lock: Mutex::new(()),
        })
    }

    /// Rely on `cargo add` to install dependencies in your sandbox
    ///
    /// https://doc.rust-lang.org/cargo/commands/cargo-add.html
    pub fn deps(self, deps: &[&str]) -> Result<Self> {
        let Self { lock, root_dir } = &self;
        let lock = lock.lock().unwrap();
        for dep in deps {
            Command::new("cargo")
                .args(["add", dep])
                .current_dir(root_dir)
                .output()?;
        }
        drop(lock);
        Ok(self)
    }

    /// Evaluate in the Sandbox a given Rust expression
    ///
    /// `quote! { }` would help you to generate a `proc_macro2::TokenStream`
    pub fn eval<T: FromStr + ToString>(&self, expr: TokenStream) -> Result<T> {
        let Self { lock, root_dir } = self;
        let _lock = lock.lock().unwrap();
        let wrapper = quote! {
            use std::io::prelude::*;
            fn main() -> std::io::Result<()> {
                let mut file = std::fs::File::create("output")?;
                let output = { #expr }.to_string();
                file.write_all(output.as_bytes())?;
                Ok(())
            }
        };
        fs::write(root_dir.join("src/main.rs"), wrapper.to_string())?;
        Command::new("cargo")
            .arg("run")
            .current_dir(root_dir)
            .output()?;
        let output = fs::read_to_string(root_dir.join("output"))?
            .parse()
            .or(Err(io::ErrorKind::Other))?;
        fs::remove_file(root_dir.join("output"))?;
        Ok(output)
    }
}