3 files changed, 128 insertions, 10 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 5d50a766f..b2d4569b3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -22,6 +22,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "33954243bd79057c2de7338850b85983a44588021f8a5fee574a8888c6de4344"
 
 [[package]]
+name = "arrayref"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4c527152e37cf757a3f78aae5a06fbeefdb07ccc535c980a3208ee3060dd544"
+
+[[package]]
 name = "arrayvec"
 version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -68,6 +74,12 @@ dependencies = [
 
 [[package]]
 name = "base64"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b41b7ea54a0c9d92199de89e20e58d49f02f8e699814ef3fdf266f6f748d15c7"
+
+[[package]]
+name = "base64"
 version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7d5ca2cd0adc3f48f9e9ea5a6bbdf9ccc0bfade884847e484d452414c7ccffb3"
@@ -79,6 +91,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
 
 [[package]]
+name = "blake2b_simd"
+version = "0.5.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d8fb2d74254a3a0b5cac33ac9f8ed0e44aa50378d9dbb2e5d83bd21ed1dc2c8a"
+dependencies = [
+ "arrayref",
+ "arrayvec",
+ "constant_time_eq",
+]
+
+[[package]]
 name = "bstr"
 version = "0.2.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -213,6 +236,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "constant_time_eq"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "245097e9a4535ee1e3e3931fcfcd55a796a44c643e8596ff6566d68f09b87bbc"
+
+[[package]]
 name = "crossbeam"
 version = "0.7.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -290,6 +319,28 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "524cbf6897b527295dff137cec09ecf3a05f4fddffd7dfcd1585403449e74198"
 
 [[package]]
+name = "dirs"
+version = "2.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "13aea89a5c93364a98e9b37b2fa237effbb694d5cfe01c5b70941f7eb087d5e3"
+dependencies = [
+ "cfg-if",
+ "dirs-sys",
+]
+
+[[package]]
+name = "dirs-sys"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "afa0b23de8fd801745c471deffa6e12d248f962c9fd4b4c33787b055599bde7b"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "redox_users",
+ "winapi 0.3.8",
+]
+
+[[package]]
 name = "drop_bomb"
 version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -659,7 +710,7 @@ version = "0.74.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "57c0e6a2b8837d27b29deb3f3e6dc1c6d2f57947677f9be1024e482ec5b59525"
 dependencies = [
- "base64",
+ "base64 0.12.0",
  "bitflags",
  "serde",
  "serde_json",
@@ -1158,6 +1209,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "cargo_metadata",
+ "dirs",
  "log",
  "ra_arena",
  "ra_cfg",
@@ -1299,6 +1351,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2439c63f3f6139d1b57529d16bc3b8bb855230c8efcc5d3a896c8bea7c3b1e84"
 
 [[package]]
+name = "redox_users"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09b23093265f8d200fa7b4c2c76297f47e681c655f6f1285a8780d6a022f7431"
+dependencies = [
+ "getrandom",
+ "redox_syscall",
+ "rust-argon2",
+]
+
+[[package]]
 name = "regex"
 version = "1.3.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1383,6 +1446,18 @@ dependencies = [
 ]
 
 [[package]]
+name = "rust-argon2"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2bc8af4bda8e1ff4932523b94d3dd20ee30a87232323eda55903ffd71d2fb017"
+dependencies = [
+ "base64 0.11.0",
+ "blake2b_simd",
+ "constant_time_eq",
+ "crossbeam-utils",
+]
+
+[[package]]
 name = "rustc-ap-rustc_lexer"
 version = "656.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/crates/ra_project_model/Cargo.toml b/crates/ra_project_model/Cargo.toml
index 5e651fe70..91958ed94 100644
--- a/crates/ra_project_model/Cargo.toml
+++ b/crates/ra_project_model/Cargo.toml
@@ -22,3 +22,5 @@ serde = { version = "1.0.106", features = ["derive"] }
 serde_json = "1.0.48"
 
 anyhow = "1.0.26"
+
+dirs = "2.0"
diff --git a/crates/ra_project_model/src/cargo_workspace.rs b/crates/ra_project_model/src/cargo_workspace.rs
index 59f46a2a0..a15a8c68e 100644
--- a/crates/ra_project_model/src/cargo_workspace.rs
+++ b/crates/ra_project_model/src/cargo_workspace.rs
@@ -8,7 +8,7 @@ use std::{
     process::Command,
 };
 
-use anyhow::{Context, Result};
+use anyhow::{Context, Error, Result};
 use cargo_metadata::{BuildScript, CargoOpt, Message, MetadataCommand, PackageId};
 use ra_arena::{Arena, Idx};
 use ra_db::Edition;
@@ -145,12 +145,8 @@ impl CargoWorkspace {
         cargo_toml: &Path,
         cargo_features: &CargoConfig,
     ) -> Result<CargoWorkspace> {
-        let _ = Command::new(cargo_binary())
-            .arg("--version")
-            .output()
-            .context("failed to run `cargo --version`, is `cargo` in PATH?")?;
-
         let mut meta = MetadataCommand::new();
+        meta.cargo_path(cargo_binary()?);
         meta.manifest_path(cargo_toml);
         if cargo_features.all_features {
             meta.features(CargoOpt::AllFeatures);
@@ -288,7 +284,7 @@ pub fn load_extern_resources(
     cargo_toml: &Path,
     cargo_features: &CargoConfig,
 ) -> Result<ExternResources> {
-    let mut cmd = Command::new(cargo_binary());
+    let mut cmd = Command::new(cargo_binary()?);
     cmd.args(&["check", "--message-format=json", "--manifest-path"]).arg(cargo_toml);
     if cargo_features.all_features {
         cmd.arg("--all-features");
@@ -337,6 +333,51 @@ fn is_dylib(path: &Path) -> bool {
     }
 }
 
-fn cargo_binary() -> String {
-    env::var("CARGO").unwrap_or_else(|_| "cargo".to_string())
+/// Return a `String` to use for executable `cargo`.
+///
+/// E.g., this may just be `cargo` if that gives a valid Cargo executable; or it
+/// may be a full path to a valid Cargo.
+fn cargo_binary() -> Result<String> {
+    // The current implementation checks three places for a `cargo` to use:
+    // 1) $CARGO environment variable (erroring if this is set but not a usable Cargo)
+    // 2) `cargo`
+    // 3) `~/.cargo/bin/cargo`
+    if let Ok(path) = env::var("CARGO") {
+        if is_valid_cargo(&path) {
+            Ok(path)
+        } else {
+            Err(Error::msg("`CARGO` environment variable points to something that's not a valid Cargo executable"))
+        }
+    } else {
+        let final_path: Option<String> = if is_valid_cargo("cargo") {
+            Some("cargo".to_owned())
+        } else {
+            if let Some(mut path) = dirs::home_dir() {
+                path.push(".cargo");
+                path.push("bin");
+                path.push("cargo");
+                if is_valid_cargo(&path) {
+                    Some(path.into_os_string().into_string().expect("Invalid Unicode in path"))
+                } else {
+                    None
+                }
+            } else {
+                None
+            }
+        };
+        final_path.ok_or(
+            // This error message may also be caused by $PATH or $CARGO 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 and $CARGO from that terminal; but
+            // launching VSCode from Dock does not inherit environment variables from a terminal.
+            // For more discussion, see #3118.
+            Error::msg("Failed to find `cargo` executable. Make sure `cargo` is in `$PATH`, or set `$CARGO` to point to a valid Cargo executable.")
+        )
+    }
+}
+
+/// Does the given `Path` point to a usable `Cargo`?
+fn is_valid_cargo(p: impl AsRef<Path>) -> bool {
+    Command::new(p.as_ref()).arg("--version").output().is_ok()
 }