feat(rust): Support new rust-toolchain format (#1938)

* feat(rust): Support new rust-toolchain format

* Match file parsing with rustup and update link

* Use cargo to deserialize the rust-toolchain file

* Filter empty channel strings after extraction

* Use the option value instead of rewrapping

3 files changed, 80 insertions, 14 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 0ded37a95..bdae9630c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1122,18 +1122,18 @@ dependencies = [
 
 [[package]]
 name = "serde"
-version = "1.0.116"
+version = "1.0.117"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "96fe57af81d28386a513cbc6858332abc6117cfdb5999647c6444b8f43a370a5"
+checksum = "b88fa983de7720629c9387e9f517353ed404164b1e482c970a90c1a4aaf7dc1a"
 dependencies = [
  "serde_derive",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.116"
+version = "1.0.117"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f630a6370fd8e457873b4bd2ffdae75408bc291ba72be773772a4c2a065d9ae8"
+checksum = "cbd1ae72adb44aab48f325a02444a5fc079349a8d804c1fc922aed3f7454c74e"
 dependencies = [
  "proc-macro2",
  "quote 1.0.7",
@@ -1210,7 +1210,7 @@ dependencies = [
  "rayon",
  "regex",
  "rust-ini",
- "serde_derive",
+ "serde",
  "serde_json",
  "shell-words",
  "starship_module_config_derive",
diff --git a/Cargo.toml b/Cargo.toml
index 23facdb84..5e348a9b8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -33,7 +33,7 @@ ansi_term = "0.12.1"
 dirs-next = "2.0.0"
 git2 = { version = "0.13.12", default-features = false }
 toml = { version = "0.5.7", features = ["preserve_order"] }
-rust-ini = "0.16" 
+rust-ini = "0.16"
 serde_json = "1.0.59"
 rayon = "1.5.0"
 log = { version = "0.4.11", features = ["std"] }
@@ -59,7 +59,7 @@ unicode-width = "0.1.8"
 term_size = "0.3.2"
 quick-xml = "0.20.0"
 rand = "0.7.3"
-serde_derive = "1.0.115"
+serde = { version = "1.0.117", features = ["derive"] }
 indexmap = "1.6.0"
 notify-rust = { version = "4.0.0", optional = true }
 
diff --git a/src/modules/rust.rs b/src/modules/rust.rs
index c72be0ec8..00b029a82 100644
--- a/src/modules/rust.rs
+++ b/src/modules/rust.rs
@@ -2,6 +2,8 @@ use std::fs;
 use std::path::Path;
 use std::process::{Command, Output};
 
+use serde::Deserialize;
+
 use super::{Context, Module, RootModuleConfig};
 
 use crate::configs::rust::RustConfig;
@@ -125,26 +127,47 @@ fn extract_toolchain_from_rustup_override_list(stdout: &str, cwd: &Path) -> Opti
 
 fn find_rust_toolchain_file(context: &Context) -> Option<String> {
     // Look for 'rust-toolchain' as rustup does.
-    // https://github.com/rust-lang/rustup.rs/blob/d84e6e50126bccd84649e42482fc35a11d019401/src/config.rs#L320-L358
+    // https://github.com/rust-lang/rustup/blob/89912c4cf51645b9c152ab7380fd07574fec43a3/src/config.rs#L546-L616
+
+    #[derive(Deserialize)]
+    struct OverrideFile {
+        toolchain: ToolchainSection,
+    }
 
-    fn read_first_line(path: &Path) -> Option<String> {
-        let content = fs::read_to_string(path).ok()?;
-        let line = content.lines().next()?;
-        Some(line.trim().to_owned())
+    #[derive(Deserialize)]
+    struct ToolchainSection {
+        channel: Option<String>,
+    }
+
+    fn read_channel(path: &Path) -> Option<String> {
+        let contents = fs::read_to_string(path).ok()?;
+
+        match contents.lines().count() {
+            0 => None,
+            1 => Some(contents),
+            _ => {
+                toml::from_str::<OverrideFile>(&contents)
+                    .ok()?
+                    .toolchain
+                    .channel
+            }
+        }
+        .filter(|c| !c.trim().is_empty())
+        .map(|c| c.trim().to_owned())
     }
 
     if let Ok(true) = context
         .dir_contents()
         .map(|dir| dir.has_file("rust-toolchain"))
     {
-        if let Some(toolchain) = read_first_line(Path::new("rust-toolchain")) {
+        if let Some(toolchain) = read_channel(Path::new("rust-toolchain")) {
             return Some(toolchain);
         }
     }
 
     let mut dir = &*context.current_dir;
     loop {
-        if let Some(toolchain) = read_first_line(&dir.join("rust-toolchain")) {
+        if let Some(toolchain) = read_channel(&dir.join("rust-toolchain")) {
             return Some(toolchain);
         }
         dir = dir.parent()?;
@@ -200,6 +223,7 @@ enum RustupRunRustcVersionOutcome {
 #[cfg(test)]
 mod tests {
     use once_cell::sync::Lazy;
+    use std::io;
     use std::process::{ExitStatus, Output};
 
     use super::*;
@@ -309,4 +333,46 @@ mod tests {
         let version_without_hash = String::from("rustc 1.34.0");
         assert_eq!(format_rustc_version(version_without_hash), "v1.34.0");
     }
+
+    #[test]
+    fn test_find_rust_toolchain_file() -> io::Result<()> {
+        let dir = tempfile::tempdir()?;
+        fs::write(dir.path().join("rust-toolchain"), "1.34.0")?;
+
+        let context = Context::new_with_dir(Default::default(), dir.path());
+
+        assert_eq!(
+            find_rust_toolchain_file(&context),
+            Some("1.34.0".to_owned())
+        );
+        dir.close()?;
+
+        let dir = tempfile::tempdir()?;
+        fs::write(
+            dir.path().join("rust-toolchain"),
+            "[toolchain]\nchannel = \"1.34.0\"",
+        )?;
+
+        let context = Context::new_with_dir(Default::default(), dir.path());
+
+        assert_eq!(
+            find_rust_toolchain_file(&context),
+            Some("1.34.0".to_owned())
+        );
+        dir.close()?;
+
+        let dir = tempfile::tempdir()?;
+        fs::write(
+            dir.path().join("rust-toolchain"),
+            "\n\n[toolchain]\n\n\nchannel = \"1.34.0\"",
+        )?;
+
+        let context = Context::new_with_dir(Default::default(), dir.path());
+
+        assert_eq!(
+            find_rust_toolchain_file(&context),
+            Some("1.34.0".to_owned())
+        );
+        dir.close()
+    }
 }