From c63e9a71bd958c576100fbbeaf5723bb22450fd9 Mon Sep 17 00:00:00 2001
From: Denis Cornehl <denis@cornehl.org>
Date: Tue, 28 Dec 2021 21:10:49 +0100
Subject: [PATCH] perf(rust): additionally check `rustup default` for faster
 result. (#3354)

* perf(rust): additionally check `rustup default` for faster result.

After checking directory overrides we were directly falling back to the
relatively slow call to `rustc --version`.

Inserting a call to `rustup default` leads to a quicker response.

* use `context.exec_cmd` instead of `create_command`
---
 src/modules/rust.rs | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/modules/rust.rs b/src/modules/rust.rs
index 48352017b..58a75ad38 100644
--- a/src/modules/rust.rs
+++ b/src/modules/rust.rs
@@ -65,6 +65,7 @@ fn get_module_version(context: &Context, config: &RustConfig) -> Option<String>
     // 1. `$RUSTUP_TOOLCHAIN`
     // 2. `rustup override list`
     // 3. `rust-toolchain` or `rust-toolchain.toml` in `.` or parent directories
+    // 4. `rustup default`
     // as `rustup` does.
     // https://github.com/rust-lang/rustup.rs/tree/eb694fcada7becc5d9d160bf7c623abe84f8971d#override-precedence
     //
@@ -74,8 +75,9 @@ fn get_module_version(context: &Context, config: &RustConfig) -> Option<String>
     // - `rustup show active-toolchain`
     // - `rustup which`
     if let Some(toolchain) = env_rustup_toolchain(context)
-        .or_else(|| execute_rustup_override_list(&context.current_dir))
+        .or_else(|| execute_rustup_override_list(context))
         .or_else(|| find_rust_toolchain_file(context))
+        .or_else(|| execute_rustup_default(context))
     {
         match execute_rustup_run_rustc_version(&toolchain) {
             RustupRunRustcVersionOutcome::RustcVersion(rustc_version) => {
@@ -99,14 +101,22 @@ fn env_rustup_toolchain(context: &Context) -> Option<String> {
     Some(val.trim().to_owned())
 }
 
-fn execute_rustup_override_list(cwd: &Path) -> Option<String> {
-    let Output { stdout, .. } = create_command("rustup")
-        .ok()?
-        .args(&["override", "list"])
-        .output()
-        .ok()?;
-    let stdout = String::from_utf8(stdout).ok()?;
-    extract_toolchain_from_rustup_override_list(&stdout, cwd)
+fn execute_rustup_override_list(context: &Context) -> Option<String> {
+    extract_toolchain_from_rustup_override_list(
+        &context.exec_cmd("rustup", &["override", "list"])?.stdout,
+        &context.current_dir,
+    )
+}
+
+fn execute_rustup_default(context: &Context) -> Option<String> {
+    // `rustup default` output is:
+    //    stable-x86_64-apple-darwin (default)
+    context
+        .exec_cmd("rustup", &["default"])?
+        .stdout
+        .split_whitespace()
+        .next()
+        .map(str::to_owned)
 }
 
 fn extract_toolchain_from_rustup_override_list(stdout: &str, cwd: &Path) -> Option<String> {