fix(noImportCycles): prevent flagging on single file import cycling (#6765)

Co-authored-by: Arend van Beelen jr. <[email protected]>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Emanuele Stoppa <[email protected]>

Author: 4 people

.changeset/icy-results-wonder.md

@@ -0,0 +1,23 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed [#6569](https://github.com/biomejs/biome/issues/6569): Allow files to export from themselves with `noImportCycles`.
+
+This means the following is now allowed:
+
+```js
+// example.js
+export function example() {
+  return 1;
+}
+
+// Re-exports all named exports from the current module under a single namespace
+// and then imports the namespace from the current module.
+// Allows for encapsulating functions/variables into a namespace instead
+// of using a static class.
+export * as Example from './example.js';
+
+import { Example } from './example.js';
+```
+```

crates/biome_js_analyze/src/lint/nursery/no_import_cycles.rs

@@ -25,6 +25,10 @@ declare_lint_rule! {
     /// only go in a single direction, i.e. they don't point "back" to the
     /// importing file.
     ///
+    /// However, files that import themselves are allowed, and the rule won't trigger for these use cases.
+    /// This allows for encapsulation of functions/variables into a namespace instead of using a
+    /// static class (triggers [noStaticOnlyClass](https://biomejs.dev/linter/rules/no-static-only-class)).
+    ///
     /// :::note
     /// This rule is computationally expensive. If you are particularly
     /// pressed for lint time, or don't think you have an issue with dependency
@@ -79,6 +83,16 @@ declare_lint_rule! {
     /// }
     /// ```
     ///
+    /// ```js,file=foobaz.js
+    /// export function foo() {
+    ///     console.log("foobaz");
+    /// }
+    ///
+    /// export * as baz from './foobaz.js';
+    ///
+    /// import { baz } from './foobaz.js';
+    /// ```
+    ///
     /// ```ts,file=types.ts
     /// import type { bar } from "./qux.ts";
     ///
@@ -243,6 +257,12 @@ fn find_cycle(
             }
 
             if path == ctx.file_path() {
+                // https://github.com/biomejs/biome/issues/6569
+                // prevent flagging on import cycles when they are isolated to a single file
+                if stack.is_empty() && start_path == path {
+                    continue;
+                }
+
                 // Return all the paths from `start_path` to `resolved_path`:
                 let paths = Some(start_path.to_string())
                     .into_iter()
@@ -254,6 +274,7 @@ fn find_cycle(
                     )
                     .chain(Some(path.to_string()))
                     .collect();
+
                 return Some(paths);
             }
 

crates/biome_js_analyze/tests/specs/nursery/noImportCycles/valid.js

@@ -3,3 +3,13 @@
 import { foo } from "./invalidFoobar";
 
 foo();
+
+export function bar() {
+  return 1;
+}
+
+export * as bar from "./valid"
+
+import { foobar } from "./valid"
+
+foobar.bar();

crates/biome_js_analyze/tests/specs/nursery/noImportCycles/valid.js.snap

@@ -10,4 +10,14 @@ import { foo } from "./invalidFoobar";
 
 foo();
 
+export function bar() {
+  return 1;
+}
+
+export * as bar from "./valid"
+
+import { foobar } from "./valid"
+
+foobar.bar();
+
 ```