fix(biome-js-analyze): add tests for useReadonlyClassProperties

.changeset/use_readonly_class_properties_nested_assignment_fix.md

@@ -0,0 +1,18 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed [#7310](https://github.com/biomejs/biome/issues/7310): [`useReadonlyClassProperties`](https://biomejs.dev/linter/rules/use-readonly-class-properties/) correctly handles nested assignments, avoiding false positives when a class property is assigned within another assignment expression.
+
+Example of code that previously triggered a false positive but is now correctly ignored:
+
+```ts
+class test {
+  private thing: number = 0; // incorrectly flagged
+
+  public incrementThing(): void {
+    const temp = {x: 0};
+    temp.x = this.thing++;
+  }
+}
+```

crates/biome_js_analyze/tests/specs/style/useReadonlyClassProperties/valid.ts

@@ -664,3 +664,24 @@ export class ToastService {
 		this.activeToasts.push({id, message, type, autoClose});
 	}
 }
+
+class TestIncrementInAssignment {
+	private thing: number = 0;
+
+	public incrementThing(): void {
+		const temp = { x: 0 };
+		temp.x = this.thing++;
+	}
+}
+
+class TesAssignmentInNestedCallback {
+	private thing: any;
+
+	public doStuff(): void {
+		ui.showText("example", {
+			callback: () => {
+				this.thing = x;
+			},
+		});
+	}
+}

crates/biome_js_analyze/tests/specs/style/useReadonlyClassProperties/valid.ts.snap

@@ -1,6 +1,6 @@
 ---
 source: crates/biome_js_analyze/tests/spec_tests.rs
-assertion_line: 146
+assertion_line: 152
 expression: valid.ts
 ---
 # Input
@@ -672,4 +672,25 @@ export class ToastService {
 	}
 }
 
+class TestIncrementInAssignment {
+	private thing: number = 0;
+
+	public incrementThing(): void {
+		const temp = { x: 0 };
+		temp.x = this.thing++;
+	}
+}
+
+class TesAssignmentInNestedCallback {
+	private thing: any;
+
+	public doStuff(): void {
+		ui.showText("example", {
+			callback: () => {
+				this.thing = x;
+			},
+		});
+	}
+}
+
 ```