fix(linter): Fix the behavior of import/extensions rule for a file that has multiple extensions. (#18919)

See #18918 for details and a test repo. This fixes the problematic behavior of the Oxlint implementation so we match the implementation from the original import plugin.

Basically, we want to have `tsx: never` in the rule config, and in that case it should disallow this:

```tsx
import Foo from "./Foo.stories.tsx";
```

It correctly did that, but if you _removed_ the `tsx` extension, you would end up with an error about not allowing the `stories` extension, which was nonsensical. Now we correctly handle this behavior, so `import Foo from "./Foo.stories";` is allowed for this config setting.

Built with Claude Code, reviewed and tested by me. [Another user also confirmed that this fixes the problem for them](#18681 (comment)).

Fixes #18918 and #18681.

Author: connorshea

crates/oxc_linter/fixtures/import/Component.stories.tsx

@@ -0,0 +1 @@
+export const Component = () => <div>Component</div>;

crates/oxc_linter/fixtures/import/helper.spec.js

@@ -0,0 +1,3 @@
+export function helper() {
+  return 'helper';
+}

crates/oxc_linter/fixtures/import/utils.test.ts

@@ -0,0 +1,3 @@
+export function testUtil() {
+  return 'test';
+}

crates/oxc_linter/src/rules/import/extensions.rs

@@ -540,15 +540,27 @@ impl Extensions {
                 return;
             }
 
+            // Determine if the extension being checked is actually written in the import
+            // For files with multiple extensions (e.g., foo.stories.tsx), we need to check
+            // if the ACTUAL file extension (resolved) matches what's written in the import.
+            // If resolved is "tsx" but written is "stories", then tsx is NOT written.
+            let extension_is_written = if let Some(resolved) = resolved_extension {
+                // If we have a resolved extension, check if it matches the written extension
+                written_extension == Some(resolved)
+            } else {
+                // Otherwise, just check if there's any written extension
+                written_extension.is_some()
+            };
+
             if config.should_flag_extension(
                 ext_str,
-                written_extension.is_some(),
+                extension_is_written,
                 resolved_extension.is_some(),
                 require_extension,
             ) {
-                if let Some(ext) = written_extension {
+                if extension_is_written {
                     ctx.diagnostic(extension_should_not_be_included_in_diagnostic(
-                        span, ext, is_import,
+                        span, ext_str, is_import,
                     ));
                 } else {
                     ctx.diagnostic(extension_missing_diagnostic(span, is_import));
@@ -1217,6 +1229,11 @@ fn test() {
             r#"import data from "./data.json" with { type: "json" };"#,
             Some(json!(["ignorePackages"])),
         ),
+        // Files with multiple extensions (e.g., Component.stories.tsx)
+        // These test cases use actual fixture files for proper module resolution
+        (r"import { Component } from './Component.stories';", Some(json!([{ "tsx": "never" }]))),
+        (r"import { testUtil } from './utils.test';", Some(json!([{ "ts": "never" }]))),
+        (r"import { helper } from './helper.spec';", Some(json!([{ "js": "never" }]))),
         // Subpath imports
         // https://nodejs.org/api/packages.html#subpath-imports
         // (
@@ -1685,6 +1702,16 @@ fn test() {
             r"import useState from '@foo/bar/useState.ts';",
             Some(json!(["never", { "ignorePackages": true }])),
         ),
+        // Files with multiple extensions - should fail when actual extension IS included
+        (
+            r"import Component from './Component.stories.tsx';",
+            Some(json!(["never", { "tsx": "never" }])),
+        ),
+        (
+            r"import Component from './Component.test.ts';",
+            Some(json!(["never", { "ts": "never" }])),
+        ),
+        (r"import utils from './utils.spec.js';", Some(json!(["never", { "js": "never" }]))),
         // TODO: This should probably fail? Needs further investigation.
         // (
         //     r"import useState from '@foo/bar/useState';",

crates/oxc_linter/src/snapshots/import_extensions.snap

@@ -693,3 +693,24 @@ source: crates/oxc_linter/src/tester.rs
    · ────────────────────────────────────────────
    ╰────
   help: Remove the file extension from this import.
+
+  ⚠ eslint-plugin-import(extensions): File extension "tsx" should not be included in the import declaration.
+   ╭─[extensions.tsx:1:1]
+ 1 │ import Component from './Component.stories.tsx';
+   · ────────────────────────────────────────────────
+   ╰────
+  help: Remove the file extension from this import.
+
+  ⚠ eslint-plugin-import(extensions): File extension "ts" should not be included in the import declaration.
+   ╭─[extensions.tsx:1:1]
+ 1 │ import Component from './Component.test.ts';
+   · ────────────────────────────────────────────
+   ╰────
+  help: Remove the file extension from this import.
+
+  ⚠ eslint-plugin-import(extensions): File extension "js" should not be included in the import declaration.
+   ╭─[extensions.tsx:1:1]
+ 1 │ import utils from './utils.spec.js';
+   · ────────────────────────────────────
+   ╰────
+  help: Remove the file extension from this import.