feat(no-misused-observables): variable declarations

Author: JasonWeinzierl

src/rules/no-misused-observables.ts

@@ -65,7 +65,7 @@ export const noMisusedObservablesRule = ruleCreator({
       Property: checkProperty,
       ReturnStatement: checkReturnStatement,
       AssignmentExpression: checkAssignment,
-      // VariableDeclarator: checkVariableDeclarator,
+      VariableDeclarator: checkVariableDeclaration,
     };
 
     const spreadChecks: eslint.RuleListener = {
@@ -237,6 +237,34 @@ export const noMisusedObservablesRule = ruleCreator({
       }
     }
 
+    function checkVariableDeclaration(node: es.VariableDeclarator): void {
+      const tsNode = esTreeNodeToTSNodeMap.get(node);
+      if (
+        tsNode.initializer === undefined
+        || !node.init
+        || !node.id.typeAnnotation
+      ) {
+        return;
+      }
+
+      // Optimization to avoid touching type info.
+      if (!isPossiblyFunctionType(node.id.typeAnnotation)) {
+        return;
+      }
+
+      const varType = getTypeAtLocation(node.id);
+      if (!isVoidReturningFunctionType(varType)) {
+        return;
+      }
+
+      if (couldReturnObservable(node.init)) {
+        context.report({
+          messageId: 'forbiddenVoidReturnVariable',
+          node: node.init,
+        });
+      }
+    }
+
     return {
       ...(checksVoidReturn ? voidReturnChecks : {}),
       ...(checksSpreads ? spreadChecks : {}),

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

@@ -213,6 +213,7 @@ ruleTester({ types: true }).run('no-misused-observables', noMisusedObservablesRu
 
         let foo: () => void;
         foo = (): Observable<number> => of(42);
+        const bar: () => void = (): Observable<number> => of(42);
       `,
       options: [{ checksVoidReturn: false }],
     },
@@ -756,6 +757,17 @@ ruleTester({ types: true }).run('no-misused-observables', noMisusedObservablesRu
               ~~~~~~~~~~~~ [forbiddenVoidReturnVariable]
       `,
     ),
+    fromFixture(
+      stripIndent`
+        // void return variable; const
+        import { of } from "rxjs";
+
+        const foo: () => void = () => of(42);
+                                ~~~~~~~~~~~~ [forbiddenVoidReturnVariable]
+        const bar = () => of(42), baz: () => void = () => of(42);
+                                                    ~~~~~~~~~~~~ [forbiddenVoidReturnVariable]
+      `,
+    ),
     fromFixture(
       stripIndent`
         // void return variable; nested