fix(linter/plugins): output warning on first JS plugin load (#14165)

Oxlint outputs a warning "JS plugins are experimental" when there's a config containing `jsPlugins`. Output this warning before trying to load the first plugin, so that you still get the warning even if there's an error loading it. The warning may be particularly relevant in this case!

Author: overlookmotel

apps/oxlint/src/lint.rs

@@ -238,13 +238,6 @@ impl CliRunner {
         let mut external_linter = self.external_linter;
         if external_plugin_store.is_empty() {
             external_linter = None;
-        } else {
-            #[expect(clippy::print_stderr)]
-            {
-                eprintln!(
-                    "WARNING: JS plugins are experimental and not subject to semver.\nBreaking changes are possible while JS plugins support is under development."
-                );
-            }
         }
 
         if let Some(basic_config_file) = oxlintrc_for_print {

apps/oxlint/test/fixtures/custom_plugin_import_error/output.snap.md

@@ -12,4 +12,6 @@ Failed to parse configuration file.
 
 # stderr
 ```
+WARNING: JS plugins are experimental and not subject to semver.
+Breaking changes are possible while JS plugins support is under development.
 ```

apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/output.snap.md

@@ -12,4 +12,6 @@ Failed to parse configuration file.
 
 # stderr
 ```
+WARNING: JS plugins are experimental and not subject to semver.
+Breaking changes are possible while JS plugins support is under development.
 ```

apps/oxlint/test/fixtures/custom_plugin_missing_rule/output.snap.md

@@ -10,4 +10,6 @@ Failed to parse configuration file.
 
 # stderr
 ```
+WARNING: JS plugins are experimental and not subject to semver.
+Breaking changes are possible while JS plugins support is under development.
 ```

apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/output.snap.md

@@ -10,4 +10,6 @@ Failed to build configuration.
 
 # stderr
 ```
+WARNING: JS plugins are experimental and not subject to semver.
+Breaking changes are possible while JS plugins support is under development.
 ```

apps/oxlint/test/fixtures/missing_custom_plugin/output.snap.md

@@ -11,4 +11,6 @@ Failed to parse configuration file.
 
 # stderr
 ```
+WARNING: JS plugins are experimental and not subject to semver.
+Breaking changes are possible while JS plugins support is under development.
 ```

crates/oxc_linter/src/config/config_builder.rs

@@ -499,6 +499,14 @@ impl ConfigStoreBuilder {
     ) -> Result<(), ConfigBuilderError> {
         use crate::PluginLoadResult;
 
+        // Print warning on 1st attempt to load a plugin
+        #[expect(clippy::print_stderr)]
+        if external_plugin_store.is_empty() {
+            eprintln!(
+                "WARNING: JS plugins are experimental and not subject to semver.\nBreaking changes are possible while JS plugins support is under development."
+            );
+        }
+
         let resolved = resolver.resolve(oxlintrc_dir_path, plugin_specifier).map_err(|e| {
             ConfigBuilderError::PluginLoadFailed {
                 plugin_specifier: plugin_specifier.to_string(),