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2024-03-25 23:21:14 +01:00

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use anyhow::{Context, Result};
use serde::Serialize;
use std::env;
use std::path::PathBuf;
use std::process::{Command, Stdio};
use crate::exercise::Exercise;
/// Contains the structure of resulting rust-project.json file
/// and functions to build the data required to create the file
struct RustAnalyzerProject {
sysroot_src: PathBuf,
crates: Vec<Crate>,
struct Crate {
root_module: PathBuf,
edition: &'static str,
// Not used, but required in the JSON file.
deps: Vec<()>,
// Only `test` is used for all crates.
// Therefore, an array is used instead of a `Vec`.
cfg: [&'static str; 1],
impl RustAnalyzerProject {
fn build(exercises: Vec<Exercise>) -> Result<Self> {
let crates = exercises
.map(|exercise| Crate {
root_module: exercise.path,
edition: "2021",
deps: Vec::new(),
// This allows rust_analyzer to work inside `#[test]` blocks
cfg: ["test"],
if let Some(path) = env::var_os("RUST_SRC_PATH") {
return Ok(Self {
sysroot_src: PathBuf::from(path),
let toolchain = Command::new("rustc")
.context("Failed to get the sysroot from `rustc`. Do you have `rustc` installed?")?
let toolchain =
String::from_utf8(toolchain).context("The toolchain path is invalid UTF8")?;
let toolchain = toolchain.trim_end();
println!("Determined toolchain: {toolchain}\n");
let mut sysroot_src = PathBuf::with_capacity(256);
sysroot_src.extend([toolchain, "lib", "rustlib", "src", "rust", "library"]);
Ok(Self {
/// Write `rust-project.json` to disk.
pub fn write_project_json(exercises: Vec<Exercise>) -> Result<()> {
let content = RustAnalyzerProject::build(exercises)?;
// Using the capacity 2^14 since the file length in bytes is higher than 2^13.
// The final length is not known exactly because it depends on the user's sysroot path,
// the current number of exercises etc.
let mut buf = Vec::with_capacity(1 << 14);
serde_json::to_writer(&mut buf, &content)?;
std::fs::write("rust-project.json", buf)?;