Make Scarb smarter when searching for Cargo binary (#1338)

This commit borrows the logic for looking for Cargo from Rust Analyzer,
via its published `ra_ap_toolchain` crate.
This change makes Scarb aware of:
1. The `CARGO` environment variable
2. The relatively well-known `$CARGO_HOME` directory

This should make Scarb succeed to run `cargo fetch`/`build` when being
run outside the interactive shell
(i.e. without environment set by `rustup`).
This includes running Scarb from CairoLS that is being run from a
desktop application (like VSCode launched from macOS Dock).

Signed-off-by: Marek Kaput <marek.kaput@swmansion.com>

Cargo.toml

@@ -92,6 +92,7 @@ petgraph = "0.6"
 predicates = "3"
 proc-macro2 = "1"
 quote = "1"
+ra_ap_toolchain = "0.0.218"
 rayon = "1.10"
 redb = "2.1.0"
 reqwest = { version = "0.11", features = ["gzip", "brotli", "deflate", "json", "stream"], default-features = false }

scarb/Cargo.toml

@@ -24,8 +24,8 @@ cairo-lang-formatter.workspace = true
 cairo-lang-macro = { path = "../plugins/cairo-lang-macro" }
 cairo-lang-macro-stable = { path = "../plugins/cairo-lang-macro-stable" }
 cairo-lang-semantic.workspace = true
-cairo-lang-sierra.workspace = true
 cairo-lang-sierra-to-casm.workspace = true
+cairo-lang-sierra.workspace = true
 cairo-lang-starknet-classes.workspace = true
 cairo-lang-starknet.workspace = true
 cairo-lang-syntax.workspace = true
@@ -51,6 +51,7 @@ libloading.workspace = true
 once_cell.workspace = true
 pathdiff.workspace = true
 petgraph.workspace = true
+ra_ap_toolchain.workspace = true
 redb.workspace = true
 reqwest.workspace = true
 scarb-build-metadata = { path = "../utils/scarb-build-metadata" }

scarb/src/compiler/plugin/proc_macro/compilation.rs

@@ -5,6 +5,7 @@ use crate::process::exec_piping;
 use anyhow::Result;
 use camino::Utf8PathBuf;
 use libloading::library_filename;
+use ra_ap_toolchain::Tool;
 use scarb_ui::{Message, OutputFormat};
 use serde::{Serialize, Serializer};
 use serde_json::value::RawValue;
@@ -118,7 +119,7 @@ impl From<OutputFormat> for CargoOutputFormat {
 
 impl From<CargoCommand> for Command {
     fn from(args: CargoCommand) -> Self {
-        let mut cmd = Command::new("cargo");
+        let mut cmd = Command::new(Tool::Cargo.path());
         cmd.current_dir(args.current_dir);
         match args.action {
             CargoAction::Fetch => cmd.arg("fetch"),