refactor(linter/plugins): improve error messages for JS plugins

crates/oxc_linter/src/config/config_builder.rs

@@ -594,11 +594,13 @@ impl Display for ConfigBuilderError {
                 write!(f, "invalid config file {file}: {reason}")
             }
             ConfigBuilderError::PluginLoadFailed { plugin_specifier, error } => {
-                write!(f, "Failed to load external plugin: {plugin_specifier}\n  {error}")?;
+                write!(f, "Failed to load JS plugin: {plugin_specifier}\n  {error}")?;
                 Ok(())
             }
             ConfigBuilderError::NoExternalLinterConfigured => {
-                f.write_str("Failed to load external plugin because no external linter was configured. This means the Oxlint binary was executed directly rather than via napi bindings.")?;
+                f.write_str(
+                    "JS plugins are not supported without `--experimental-js-plugins` CLI option",
+                )?;
                 Ok(())
             }
             ConfigBuilderError::ExternalRuleLookupError(e) => std::fmt::Display::fmt(&e, f),

napi/oxlint/test/__snapshots__/e2e.test.ts.snap

@@ -447,11 +447,18 @@ exports[`oxlint CLI > should report an error if a a rule is not found within a c
 exports[`oxlint CLI > should report an error if a custom plugin cannot be loaded 1`] = `
 "Failed to parse configuration file.
 
-  x Failed to load external plugin: ./test_plugin
+  x Failed to load JS plugin: ./test_plugin
   |   Cannot find module './test_plugin'
 "
 `;
 
+exports[`oxlint CLI > should report an error if a custom plugin in config but JS plugins are not enabled 1`] = `
+"Failed to parse configuration file.
+
+  x JS plugins are not supported without \`--experimental-js-plugins\` CLI option
+"
+`;
+
 exports[`oxlint CLI > should report an error if a rule is not found within a custom plugin 1`] = `
 "Failed to parse configuration file.
 

napi/oxlint/test/e2e.test.ts

@@ -67,6 +67,12 @@ describe('oxlint CLI', () => {
     expect(normalizeOutput(stdout)).toMatchSnapshot();
   });
 
+  it('should report an error if a custom plugin in config but JS plugins are not enabled', async () => {
+    const { stdout, exitCode } = await runOxlintWithoutPlugins('test/fixtures/basic_custom_plugin');
+    expect(exitCode).toBe(1);
+    expect(normalizeOutput(stdout)).toMatchSnapshot();
+  });
+
   it('should report an error if a custom plugin cannot be loaded', async () => {
     const { stdout, exitCode } = await runOxlint('test/fixtures/missing_custom_plugin');
     expect(exitCode).toBe(1);