feat(no-misused-observables): assignments

Author: JasonWeinzierl

src/rules/no-misused-observables.ts

@@ -49,7 +49,7 @@ export const noMisusedObservablesRule = ruleCreator({
   },
   name: 'no-misused-observables',
   create: (context) => {
-    const { program, esTreeNodeToTSNodeMap } = ESLintUtils.getParserServices(context);
+    const { program, esTreeNodeToTSNodeMap, getTypeAtLocation } = ESLintUtils.getParserServices(context);
     const checker = program.getTypeChecker();
     const { couldBeObservable, couldReturnObservable } = getTypeServices(context);
     const [config = {}] = context.options;
@@ -64,7 +64,7 @@ export const noMisusedObservablesRule = ruleCreator({
       TSInterfaceDeclaration: checkClassLikeOrInterfaceNode,
       Property: checkProperty,
       ReturnStatement: checkReturnStatement,
-      // AssignmentExpression: checkAssignment,
+      AssignmentExpression: checkAssignment,
       // VariableDeclarator: checkVariableDeclarator,
     };
 
@@ -223,6 +223,20 @@ export const noMisusedObservablesRule = ruleCreator({
       });
     }
 
+    function checkAssignment(node: es.AssignmentExpression): void {
+      const varType = getTypeAtLocation(node.left);
+      if (!isVoidReturningFunctionType(varType)) {
+        return;
+      }
+
+      if (couldReturnObservable(node.right)) {
+        context.report({
+          messageId: 'forbiddenVoidReturnVariable',
+          node: node.right,
+        });
+      }
+    }
+
     return {
       ...(checksVoidReturn ? voidReturnChecks : {}),
       ...(checksSpreads ? spreadChecks : {}),

tests/rules/no-misused-observables.test.ts

@@ -205,6 +205,30 @@ ruleTester({ types: true }).run('no-misused-observables', noMisusedObservablesRu
       }
     `,
     // #endregion valid; void return return value
+    // #region valid; void return variable
+    {
+      code: stripIndent`
+        // void return variable; explicitly allowed
+        import { Observable, of } from "rxjs";
+
+        let foo: () => void;
+        foo = (): Observable<number> => of(42);
+      `,
+      options: [{ checksVoidReturn: false }],
+    },
+    stripIndent`
+      // void return variable; not void
+      import { Observable, of } from "rxjs";
+
+      let foo: () => Observable<number>;
+      foo = () => of(42);
+    `,
+    stripIndent`
+      // void return variable; unrelated
+      let foo: () => void;
+      foo = (): number => 42;
+    `,
+    // #endregion valid; void return variable
     // #region valid; spread
     {
       code: stripIndent`
@@ -721,6 +745,40 @@ ruleTester({ types: true }).run('no-misused-observables', noMisusedObservablesRu
       `,
     ),
     // #endregion invalid; void return return value
+    // #region invalid; void return variable
+    fromFixture(
+      stripIndent`
+        // void return variable; reassign
+        import { of } from "rxjs";
+
+        let foo: () => void;
+        foo = () => of(42);
+              ~~~~~~~~~~~~ [forbiddenVoidReturnVariable]
+      `,
+    ),
+    fromFixture(
+      stripIndent`
+        // void return variable; nested
+        import { of } from "rxjs";
+
+        const foo: {
+          bar?: () => void;
+        } = {};
+        foo.bar = () => of(42);
+                  ~~~~~~~~~~~~ [forbiddenVoidReturnVariable]
+      `,
+    ),
+    fromFixture(
+      stripIndent`
+        // void return variable; Record
+        import { of } from "rxjs";
+
+        const foo: Record<string, () => void> = {};
+        foo.bar = () => of(42);
+                  ~~~~~~~~~~~~ [forbiddenVoidReturnVariable]
+      `,
+    ),
+    // #endregion invalid; void return variable
     // #region invalid; spread
     fromFixture(
       stripIndent`