Merge #4329

4329: Look for `cargo`, `rustc`, and `rustup` in standard installation path r=matklad a=cdisselkoen

Discussed in #3118.  This is approximately a 90% fix for the issue described there.

This PR creates a new crate `ra_env` with a function `get_path_for_executable()`; see docs there.  `get_path_for_executable()` improves and generalizes the function `cargo_binary()` which was previously duplicated in the `ra_project_model` and `ra_flycheck` crates.  (Both of those crates now depend on the new `ra_env` crate.)  The new function checks (e.g.) `$CARGO` and `$PATH`, but also falls back on `~/.cargo/bin` manually before erroring out.  This should allow most users to not have to worry about setting the `$CARGO` or `$PATH` variables for VSCode, which can be difficult e.g. on macOS as discussed in #3118.

I've attempted to replace all calls to `cargo`, `rustc`, and `rustup` in rust-analyzer with appropriate invocations of `get_path_for_executable()`; I don't think I've missed any in Rust code, but there is at least one invocation in TypeScript code which I haven't fixed.  (I'm not sure whether it's affected by the same problem or not.) https://github.com/rust-analyzer/rust-analyzer/blob/a4778ddb7a00f552a8e653bbf56ae9fd69cfe1d3/editors/code/src/cargo.ts#L79

I'm sure this PR could be improved a bunch, so I'm happy to take feedback/suggestions on how to solve this problem better, or just bikeshedding variable/function/crate names etc.

cc @Veetaha 

Fixes #3118.

Co-authored-by: Craig Disselkoen <[email protected]>
Co-authored-by: veetaha <[email protected]>

2 files changed, 3 insertions, 6 deletions

diff --git a/crates/ra_flycheck/Cargo.toml b/crates/ra_flycheck/Cargo.toml
index 3d5093264..d0f7fb2dc 100644
--- a/crates/ra_flycheck/Cargo.toml
+++ b/crates/ra_flycheck/Cargo.toml
@@ -14,6 +14,7 @@ log = "0.4.8"
 cargo_metadata = "0.9.1"
 serde_json = "1.0.48"
 jod-thread = "0.1.1"
+ra_env = { path = "../ra_env" }
 
 [dev-dependencies]
 insta = "0.16.0"
diff --git a/crates/ra_flycheck/src/lib.rs b/crates/ra_flycheck/src/lib.rs
index f27252949..d8b727b0e 100644
--- a/crates/ra_flycheck/src/lib.rs
+++ b/crates/ra_flycheck/src/lib.rs
@@ -4,7 +4,6 @@
 mod conv;
 
 use std::{
-    env,
     io::{self, BufRead, BufReader},
     path::PathBuf,
     process::{Command, Stdio},
@@ -17,6 +16,7 @@ use lsp_types::{
     CodeAction, CodeActionOrCommand, Diagnostic, Url, WorkDoneProgress, WorkDoneProgressBegin,
     WorkDoneProgressEnd, WorkDoneProgressReport,
 };
+use ra_env::get_path_for_executable;
 
 use crate::conv::{map_rust_diagnostic_to_lsp, MappedRustDiagnostic};
 
@@ -216,7 +216,7 @@ impl FlycheckThread {
 
         let mut cmd = match &self.config {
             FlycheckConfig::CargoCommand { command, all_targets, all_features, extra_args } => {
-                let mut cmd = Command::new(cargo_binary());
+                let mut cmd = Command::new(get_path_for_executable("cargo").unwrap());
                 cmd.arg(command);
                 cmd.args(&["--workspace", "--message-format=json", "--manifest-path"]);
                 cmd.arg(self.workspace_root.join("Cargo.toml"));
@@ -337,7 +337,3 @@ fn run_cargo(
 
     Ok(())
 }
-
-fn cargo_binary() -> String {
-    env::var("CARGO").unwrap_or_else(|_| "cargo".to_string())
-}