From 139938a22e35febe8c346e255cb6e01e14e73999 Mon Sep 17 00:00:00 2001
From: Andrew Barnes <bortstheboat@gmail.com>
Date: Sun, 12 Jul 2026 23:08:05 -0400
Subject: [PATCH] Reject unknown rust-toolchain keys

---
 src/config.rs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/config.rs b/src/config.rs
index 84e267ea42..bf448d16a8 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -40,6 +40,7 @@ enum OverrideFileConfigError {
 }
 
 #[derive(Debug, Default, Deserialize, PartialEq, Eq)]
+#[serde(deny_unknown_fields)]
 struct OverrideFile {
     toolchain: ToolchainSection,
 }
@@ -51,6 +52,7 @@ impl OverrideFile {
 }
 
 #[derive(Debug, Default, Deserialize, PartialEq, Eq)]
+#[serde(deny_unknown_fields)]
 struct ToolchainSection {
     channel: Option<String>,
     path: Option<PathBuf>,
@@ -1413,4 +1415,27 @@ channel = nightly
             Ok(OverrideFileConfigError::Parsing)
         ));
     }
+
+    #[test]
+    fn parse_toml_rejects_unknown_toolchain_key() {
+        let contents = r#"[toolchain]
+channnel = "nightly"
+"#;
+
+        let error = Cfg::parse_override_file(contents, ParseMode::OnlyToml).unwrap_err();
+        assert!(format!("{error:#}").contains("unknown field `channnel`"));
+    }
+
+    #[test]
+    fn parse_toml_rejects_unknown_top_level_key() {
+        let contents = r#"[toolchain]
+channel = "nightly"
+
+[rustup]
+version = 4
+"#;
+
+        let error = Cfg::parse_override_file(contents, ParseMode::OnlyToml).unwrap_err();
+        assert!(format!("{error:#}").contains("unknown field `rustup`"));
+    }
 }