From 03e99ef22d1c989e23bc6e63ebb1950cfc277cff Mon Sep 17 00:00:00 2001
From: Taku Kodma <79110363+risu729@users.noreply.github.com>
Date: Tue, 5 May 2026 18:50:52 +1000
Subject: [PATCH] fix(backend): reject bare package backend names

---
 e2e/backend/test_bare_backend_names |  4 ++++
 src/cli/args/backend_arg.rs         | 26 ++++++++++++++++++++++++--
 src/toolset/install_state.rs        |  5 ++++-
 3 files changed, 32 insertions(+), 3 deletions(-)
 create mode 100644 e2e/backend/test_bare_backend_names

diff --git a/e2e/backend/test_bare_backend_names b/e2e/backend/test_bare_backend_names
new file mode 100644
index 0000000000..62abea7f9b
--- /dev/null
+++ b/e2e/backend/test_bare_backend_names
@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+assert_fail "mise install cargo" "cargo not found in mise tool registry"
+assert_fail "mise install gem" "gem not found in mise tool registry"
diff --git a/src/cli/args/backend_arg.rs b/src/cli/args/backend_arg.rs
index de507ce756..f70369c068 100644
--- a/src/cli/args/backend_arg.rs
+++ b/src/cli/args/backend_arg.rs
@@ -314,8 +314,9 @@ impl BackendArg {
         }
 
         let full = self.full();
-        let backend = full.split(':').next().unwrap();
-        if let Ok(backend_type) = backend.parse() {
+        if let Some((backend, _)) = full.split_once(':')
+            && let Ok(backend_type) = backend.parse()
+        {
             return backend_type;
         }
         if config::is_loaded() && Config::get_().get_repo_url(&self.short).is_some() {
@@ -648,6 +649,27 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn test_bare_package_backend_names_are_not_implicit_tools() {
+        let _config = Config::get().await.unwrap();
+
+        for name in ["cargo", "gem"] {
+            let fa: BackendArg = name.into();
+            assert_str_eq!(name, fa.full());
+            assert_eq!(BackendType::Unknown, fa.backend_type());
+        }
+
+        let fa: BackendArg = "cargo:ripgrep".into();
+        assert_eq!(BackendType::Cargo, fa.backend_type());
+
+        let fa: BackendArg = "gem:bashly".into();
+        assert_eq!(BackendType::Gem, fa.backend_type());
+
+        let fa: BackendArg = "npm".into();
+        assert_str_eq!("npm:npm", fa.full());
+        assert_eq!(BackendType::Npm, fa.backend_type());
+    }
+
     #[tokio::test]
     async fn test_backend_arg_pathname() {
         let _config = Config::get().await.unwrap();
diff --git a/src/toolset/install_state.rs b/src/toolset/install_state.rs
index 3b3dfb7d42..cb8f878d2f 100644
--- a/src/toolset/install_state.rs
+++ b/src/toolset/install_state.rs
@@ -441,7 +441,10 @@ pub fn backend_type(short: &str) -> Result<Option<BackendType>> {
     let backend_type = list_tools()
         .get(short)
         .and_then(|ist| ist.full.as_ref())
-        .map(|full| BackendType::guess(full));
+        .and_then(|full| {
+            full.split_once(':')
+                .map(|(backend, _)| BackendType::guess(backend))
+        });
     if let Some(BackendType::Unknown) = backend_type
         && let Some((plugin_name, _)) = short.split_once(':')
         && let Some(PluginType::VfoxBackend) = get_plugin_type(plugin_name)