fix(npm): improve error message when npm/bun is not installed

e2e/backend/test_backend_missing_deps

@@ -0,0 +1,130 @@
+#!/usr/bin/env bash
+
+# Test that package manager backends show helpful errors when their dependencies are missing
+
+# Create a PATH that has mise but not package managers
+# ROOT is set by run_test script
+MISE_DIR="${CARGO_TARGET_DIR:-$ROOT/target}/debug"
+export PATH="$MISE_DIR:/usr/bin:/bin:/usr/sbin:/sbin"
+
+# Track overall test status
+TEST_FAILED=0
+
+# Helper function to check if a command exists in PATH
+check_command_missing() {
+	local cmd=$1
+	if command -v "$cmd" >/dev/null 2>&1; then
+		echo "ERROR: $cmd is found in PATH, test cannot verify missing dependency behavior"
+		exit 1
+	fi
+}
+
+# Helper function to test an expected error message
+test_error_message() {
+	local test_name=$1
+	local output=$2
+	local expected=$3
+
+	if [[ $output == *"$expected"* ]]; then
+		echo "✓ $test_name"
+	else
+		echo "ERROR: $test_name failed"
+		echo "Expected: $expected"
+		echo "Got: $output"
+		TEST_FAILED=1
+		return 1
+	fi
+}
+
+# Helper function to test a command that should fail with expected error
+test_backend_error() {
+	local backend_name=$1
+	local command=$2
+	local expected_error=$3
+
+	local output
+	if output=$(eval "$command" 2>&1); then
+		echo "ERROR: $backend_name command should have failed but succeeded"
+		TEST_FAILED=1
+		return 1
+	else
+		output=$(eval "$command" 2>&1 || true)
+		test_error_message "$backend_name shows correct error" "$output" "$expected_error"
+	fi
+}
+
+# Test npm backend
+test_npm() {
+	echo "Testing npm backend with missing npm..."
+	check_command_missing "npm"
+
+	# Test ls-remote
+	test_backend_error "npm" "mise ls-remote npm:test-package" "npm is required but not found"
+
+	# Check for helpful install instructions
+	local output
+	output=$(mise ls-remote npm:test-package 2>&1 || true)
+	test_error_message "npm suggests installing node" "$output" "mise use node@latest"
+	test_error_message "npm mentions npm is needed for queries" "$output" "npm is required for querying package information"
+
+	# Test install
+	test_backend_error "npm" "mise install npm:test-package@latest" "npm is required but not found"
+
+	# Test with bun mode enabled but npm still missing
+	echo "Testing npm backend with bun mode enabled but npm missing..."
+	export MISE_NPM_BUN=true
+	test_backend_error "npm (bun mode)" "mise ls-remote npm:test-package" "npm is required but not found"
+	output=$(mise ls-remote npm:test-package 2>&1 || true)
+	test_error_message "npm (bun mode) shows npm is required for queries" "$output" "npm is required for querying package information"
+	unset MISE_NPM_BUN
+}
+
+# Test cargo backend
+test_cargo() {
+	echo "Testing cargo backend with missing cargo..."
+
+	# Remove cargo from PATH if it exists
+	local new_path=""
+	local IFS=':'
+	read -ra PATHS <<<"$PATH"
+	for p in "${PATHS[@]}"; do
+		if [[ ! -x "$p/cargo" ]]; then
+			[[ -z $new_path ]] && new_path="$p" || new_path="$new_path:$p"
+		fi
+	done
+	export PATH="$new_path"
+
+	check_command_missing "cargo"
+	test_backend_error "cargo" "mise install cargo:tiny@latest" "cargo is required but not found"
+}
+
+# Test go backend
+test_go() {
+	echo "Testing go backend with missing go..."
+
+	# Remove go from PATH if it exists
+	local new_path=""
+	local IFS=':'
+	read -ra PATHS <<<"$PATH"
+	for p in "${PATHS[@]}"; do
+		if [[ ! -x "$p/go" ]]; then
+			[[ -z $new_path ]] && new_path="$p" || new_path="$new_path:$p"
+		fi
+	done
+	export PATH="$new_path"
+
+	check_command_missing "go"
+	test_backend_error "go" "mise ls-remote go:github.com/test/test" "go is required but not found"
+}
+
+# Run all tests
+test_npm
+test_cargo
+test_go
+
+if [ $TEST_FAILED -eq 0 ]; then
+	echo "✓ backend dependency error test passed"
+else
+	echo "✗ Some tests failed"
+	exit 1
+fi

e2e/backend/test_npm_bun

@@ -1,12 +1,80 @@
 #!/usr/bin/env bash
 
-cat >mise.toml <<EOF
-[settings.npm]
-bun = true
-EOF
+# Test that npm backend properly uses bun when configured
+# This test primarily verifies behavior when npm and/or bun are available
 
-mise use bun node
+# Ensure npm is available by installing node if needed
+if ! command -v npm >/dev/null 2>&1; then
+	echo "npm not available in test environment, installing node..."
+	# Disable GPG verification for faster test
+	export MISE_GPG_VERIFY=false
+	assert_succeed "mise use node@20"
+fi
 
-assert "mise x npm:prettier@3.1.0 -- prettier -v" "3.1.0"
-assert "FORCE_COLOR=0 mise x npm:@antfu/ni@0.21.12 -- ni -v 2>/dev/null | head -n1" "@antfu/ni  v0.21.12"
-assert_succeed "mise install npm:tldr@3.4.0"
+# Ensure bun is available
+if ! command -v bun >/dev/null 2>&1; then
+	echo "bun not available in test environment, installing..."
+	assert_succeed "mise use bun@latest"
+fi
+
+# Test 1: With npm available but bun mode disabled (default)
+echo "Testing npm backend with npm available..."
+unset MISE_NPM_BUN
+
+# Test listing versions - should succeed
+assert_succeed "mise ls-remote npm:tiny >/dev/null"
+echo "✓ npm backend lists versions using npm"
+
+# Test latest version - should succeed
+assert_succeed "mise latest npm:tiny >/dev/null"
+echo "✓ npm backend gets latest version using npm"
+
+# Test 2: With bun mode enabled - npm backend should still use npm for version queries
+echo "Testing npm backend with bun mode enabled..."
+export MISE_NPM_BUN=true
+
+# The npm backend always uses npm for version queries (bun info requires package.json)
+# This is documented in the TODOs in src/backend/npm.rs
+assert_succeed "mise ls-remote npm:tiny >/dev/null"
+echo "✓ npm backend uses npm for version queries even in bun mode"
+
+# Test latest version - should succeed
+assert_succeed "mise latest npm:tiny >/dev/null"
+echo "✓ npm backend gets latest version using npm even in bun mode"
+
+unset MISE_NPM_BUN
+
+# Test 3: Test installation with bun mode
+echo "Testing npm package installation with bun..."
+export MISE_NPM_BUN=true
+
+# Clean up any previous installation
+mise uninstall npm:tiny@latest >/dev/null 2>&1 || true
+
+# Install a small package using bun
+assert_succeed "mise install npm:tiny@latest >/dev/null 2>&1"
+echo "✓ npm backend successfully installs package using bun"
+
+# Verify the package was installed by executing it
+assert_succeed "mise exec npm:tiny@latest -- tiny --version >/dev/null"
+echo "✓ Installed package can be executed"
+
+# Clean up
+mise uninstall npm:tiny@latest >/dev/null 2>&1 || true
+
+unset MISE_NPM_BUN
+
+# Test 4: Test installation with npm mode (default)
+echo "Testing npm package installation with npm (default)..."
+
+# Clean up any previous installation
+mise uninstall npm:tiny@latest >/dev/null 2>&1 || true
+
+# Install using npm (default)
+assert_succeed "mise install npm:tiny@latest >/dev/null 2>&1"
+echo "✓ npm backend successfully installs package using npm"
+
+# Clean up
+mise uninstall npm:tiny@latest >/dev/null 2>&1 || true
+
+echo "✓ npm bun behavior test completed"

src/backend/cargo.rs

@@ -61,6 +61,16 @@ impl Backend for CargoBackend {
     }
 
     async fn install_version_(&self, ctx: &InstallContext, tv: ToolVersion) -> Result<ToolVersion> {
+        // Check if cargo is available
+        self.ensure_dependency(
+            &ctx.config,
+            "cargo",
+            "To use cargo packages with mise, you need to install Rust first:\n\
+              mise use rust@latest\n\n\
+            Or install Rust via https://rustup.rs/",
+        )
+        .await?;
+
         let config = ctx.config.clone();
         let install_arg = format!("{}@{}", self.tool_name(), tv.version);
         let registry_name = &Settings::get().cargo.registry_name;

src/backend/dotnet.rs

@@ -64,6 +64,16 @@ impl Backend for DotnetBackend {
     ) -> eyre::Result<crate::toolset::ToolVersion> {
         Settings::get().ensure_experimental("dotnet backend")?;
 
+        // Check if dotnet is available
+        self.ensure_dependency(
+            &ctx.config,
+            "dotnet",
+            "To use dotnet tools with mise, you need to install .NET SDK first:\n\
+              mise use dotnet@latest\n\n\
+            Or install .NET SDK via https://dotnet.microsoft.com/download",
+        )
+        .await?;
+
         let mut cli = CmdLineRunner::new("dotnet")
             .arg("tool")
             .arg("install")

src/backend/gem.rs

@@ -47,6 +47,15 @@ impl Backend for GemBackend {
     async fn install_version_(&self, ctx: &InstallContext, tv: ToolVersion) -> Result<ToolVersion> {
         Settings::get().ensure_experimental("gem backend")?;
 
+        // Check if gem is available
+        self.ensure_dependency(
+            &ctx.config,
+            "gem",
+            "To use gem packages with mise, you need to install Ruby first:\n\
+              mise use ruby@latest",
+        )
+        .await?;
+
         CmdLineRunner::new("gem")
             .arg("install")
             .arg(self.tool_name())

src/backend/go.rs

@@ -1,11 +1,12 @@
+use crate::backend::Backend;
 use crate::backend::backend_type::BackendType;
 use crate::cli::args::BackendArg;
 use crate::cmd::CmdLineRunner;
+use crate::config::Config;
 use crate::config::Settings;
 use crate::install_context::InstallContext;
 use crate::timeout;
 use crate::toolset::ToolVersion;
-use crate::{backend::Backend, config::Config};
 use async_trait::async_trait;
 use itertools::Itertools;
 use std::{fmt::Debug, sync::Arc};
@@ -31,6 +32,16 @@ impl Backend for GoBackend {
     }
 
     async fn _list_remote_versions(&self, config: &Arc<Config>) -> eyre::Result<Vec<String>> {
+        // Check if go is available
+        self.ensure_dependency(
+            config,
+            "go",
+            "To use go packages with mise, you need to install Go first:\n\
+              mise use go@latest\n\n\
+            Or install Go via https://go.dev/dl/",
+        )
+        .await?;
+
         timeout::run_with_timeout_async(
             async || {
                 let tool_name = self.tool_name();
@@ -87,6 +98,17 @@ impl Backend for GoBackend {
         tv: ToolVersion,
     ) -> eyre::Result<ToolVersion> {
         Settings::get().ensure_experimental("go backend")?;
+
+        // Check if go is available
+        self.ensure_dependency(
+            &ctx.config,
+            "go",
+            "To use go packages with mise, you need to install Go first:\n\
+              mise use go@latest\n\n\
+            Or install Go via https://go.dev/dl/",
+        )
+        .await?;
+
         let opts = self.ba.opts();
 
         let install = async |v| {

src/backend/mod.rs

@@ -715,6 +715,24 @@ pub trait Backend: Debug + Send + Sync {
         b.which(config, &tv, bin).await.ok().flatten()
     }
 
+    /// Check if a required dependency is available and return a helpful error if not.
+    /// This provides a consistent error message format across all backends.
+    async fn ensure_dependency(
+        &self,
+        config: &Arc<Config>,
+        program: &str,
+        install_instructions: &str,
+    ) -> eyre::Result<()> {
+        if self.dependency_which(config, program).await.is_none() {
+            bail!(
+                "{} is required but not found.\n\n{}",
+                program,
+                install_instructions
+            );
+        }
+        Ok(())
+    }
+
     async fn dependency_env(&self, config: &Arc<Config>) -> eyre::Result<BTreeMap<String, String>> {
         self.dependency_toolset(config)
             .await?