1 files changed, 68 insertions, 0 deletions

diff --git a/crates/ra_toolchain/src/lib.rs b/crates/ra_toolchain/src/lib.rs
new file mode 100644
index 000000000..110c92c88
--- /dev/null
+++ b/crates/ra_toolchain/src/lib.rs
@@ -0,0 +1,68 @@
+//! This crate contains a single public function
+//! [`get_path_for_executable`](fn.get_path_for_executable.html).
+//! See docs there for more information.
+use std::{
+    env,
+    path::{Path, PathBuf},
+    process::Command,
+};
+
+use anyhow::{bail, Result};
+
+/// Return a `PathBuf` to use for the given executable.
+///
+/// E.g., `get_path_for_executable("cargo")` may return just `cargo` if that
+/// gives a valid Cargo executable; or it may return a full path to a valid
+/// Cargo.
+pub fn get_path_for_executable(executable_name: impl AsRef<str>) -> Result<PathBuf> {
+    // The current implementation checks three places for an executable to use:
+    // 1) Appropriate environment variable (erroring if this is set but not a usable executable)
+    //      example: for cargo, this checks $CARGO environment variable; for rustc, $RUSTC; etc
+    // 2) `<executable_name>`
+    //      example: for cargo, this tries just `cargo`, which will succeed if `cargo` is on the $PATH
+    // 3) `~/.cargo/bin/<executable_name>`
+    //      example: for cargo, this tries ~/.cargo/bin/cargo
+    //      It seems that this is a reasonable place to try for cargo, rustc, and rustup
+    let executable_name = executable_name.as_ref();
+    let env_var = executable_name.to_ascii_uppercase();
+    if let Ok(path) = env::var(&env_var) {
+        if is_valid_executable(&path) {
+            Ok(path.into())
+        } else {
+            bail!(
+                "`{}` environment variable points to something that's not a valid executable",
+                env_var
+            )
+        }
+    } else {
+        if is_valid_executable(executable_name) {
+            return Ok(executable_name.into());
+        }
+        if let Some(mut path) = ::home::home_dir() {
+            path.push(".cargo");
+            path.push("bin");
+            path.push(executable_name);
+            if is_valid_executable(&path) {
+                return Ok(path);
+            }
+        }
+        // This error message may also be caused by $PATH or $CARGO/$RUSTC/etc not being set correctly
+        // for VSCode, even if they are set correctly in a terminal.
+        // On macOS in particular, launching VSCode from terminal with `code <dirname>` causes VSCode
+        // to inherit environment variables including $PATH, $CARGO, $RUSTC, etc from that terminal;
+        // but launching VSCode from Dock does not inherit environment variables from a terminal.
+        // For more discussion, see #3118.
+        bail!(
+            "Failed to find `{}` executable. Make sure `{}` is in `$PATH`, or set `${}` to point to a valid executable.",
+            executable_name, executable_name, env_var
+        )
+    }
+}
+
+/// Does the given `Path` point to a usable executable?
+///
+/// (assumes the executable takes a `--version` switch and writes to stdout,
+/// which is true for `cargo`, `rustc`, and `rustup`)
+fn is_valid_executable(p: impl AsRef<Path>) -> bool {
+    Command::new(p.as_ref()).arg("--version").output().is_ok()
+}