feat: update complexity rule for optional chaining & default values (#…

…18152)

Both, optional chaining expressions and default values (in function
parameters or descructuring expressions) increase the branching of the
code and thus the complexity is increased.

Fixes: #18060

docs/src/rules/complexity.md

@@ -57,6 +57,14 @@ function b() {
     foo ||= 1;
     bar &&= 1;
 }
+
+function c(a = {}) { // default parameter -> 2nd path
+    const { b = 'default' } = a; // default value during destructuring -> 3rd path
+}
+
+function d(a) {
+    return a?.b?.c; // optional chaining with two optional properties creates two additional branches
+}
 ```
 
 :::

lib/rules/complexity.js

@@ -109,6 +109,7 @@ module.exports = {
             IfStatement: increaseComplexity,
             WhileStatement: increaseComplexity,
             DoWhileStatement: increaseComplexity,
+            AssignmentPattern: increaseComplexity,
 
             // Avoid `default`
             "SwitchCase[test]": increaseComplexity,
@@ -120,6 +121,18 @@ module.exports = {
                 }
             },
 
+            MemberExpression(node) {
+                if (node.optional === true) {
+                    increaseComplexity();
+                }
+            },
+
+            CallExpression(node) {
+                if (node.optional === true) {
+                    increaseComplexity();
+                }
+            },
+
             onCodePathEnd(codePath, node) {
                 const complexity = complexities.pop();
 

tests/lib/rules/complexity.js

@@ -124,7 +124,25 @@ ruleTester.run("complexity", rule, {
         { code: "class C { static { if (a || b) c = d || e; } }", options: [4], languageOptions: { ecmaVersion: 2022 } },
 
         // object property options
-        { code: "function b(x) {}", options: [{ max: 1 }] }
+        { code: "function b(x) {}", options: [{ max: 1 }] },
+
+        // optional chaining
+        {
+            code: "function a(b) { b?.c; }", options: [{ max: 2 }]
+        },
+
+        // default function parameter values
+        {
+            code: "function a(b = '') {}", options: [{ max: 2 }]
+        },
+
+        // default destructuring values
+        {
+            code: "function a(b) { const { c = '' } = b; }", options: [{ max: 2 }]
+        },
+        {
+            code: "function a(b) { const [ c = '' ] = b; }", options: [{ max: 2 }]
+        }
     ],
     invalid: [
         { code: "function a(x) {}", options: [0], errors: [makeError("Function 'a'", 1, 0)] },
@@ -522,6 +540,77 @@ ruleTester.run("complexity", rule, {
         },
 
         // object property options
-        { code: "function a(x) {}", options: [{ max: 0 }], errors: [makeError("Function 'a'", 1, 0)] }
+        { code: "function a(x) {}", options: [{ max: 0 }], errors: [makeError("Function 'a'", 1, 0)] },
+
+        // optional chaining
+        {
+            code: "function a(b) { b?.c; }",
+            options: [{ max: 1 }],
+            errors: [makeError("Function 'a'", 2, 1)]
+        },
+        {
+            code: "function a(b) { b?.['c']; }",
+            options: [{ max: 1 }],
+            errors: [makeError("Function 'a'", 2, 1)]
+        },
+        {
+            code: "function a(b) { b?.c; d || e; }",
+            options: [{ max: 2 }],
+            errors: [makeError("Function 'a'", 3, 2)]
+        },
+        {
+            code: "function a(b) { b?.c?.d; }",
+            options: [{ max: 2 }],
+            errors: [makeError("Function 'a'", 3, 2)]
+        },
+        {
+            code: "function a(b) { b?.['c']?.['d']; }",
+            options: [{ max: 2 }],
+            errors: [makeError("Function 'a'", 3, 2)]
+        },
+        {
+            code: "function a(b) { b?.c?.['d']; }",
+            options: [{ max: 2 }],
+            errors: [makeError("Function 'a'", 3, 2)]
+        },
+        {
+            code: "function a(b) { b?.c.d?.e; }",
+            options: [{ max: 2 }],
+            errors: [makeError("Function 'a'", 3, 2)]
+        },
+        {
+            code: "function a(b) { b?.c?.(); }",
+            options: [{ max: 2 }],
+            errors: [makeError("Function 'a'", 3, 2)]
+        },
+        {
+            code: "function a(b) { b?.c?.()?.(); }",
+            options: [{ max: 3 }],
+            errors: [makeError("Function 'a'", 4, 3)]
+        },
+
+        // default function parameter values
+        {
+            code: "function a(b = '') {}",
+            options: [{ max: 1 }],
+            errors: [makeError("Function 'a'", 2, 1)]
+        },
+
+        // default destructuring values
+        {
+            code: "function a(b) { const { c = '' } = b; }",
+            options: [{ max: 1 }],
+            errors: [makeError("Function 'a'", 2, 1)]
+        },
+        {
+            code: "function a(b) { const [ c = '' ] = b; }",
+            options: [{ max: 1 }],
+            errors: [makeError("Function 'a'", 2, 1)]
+        },
+        {
+            code: "function a(b) { const [ { c: d = '' } = {} ] = b; }",
+            options: [{ max: 1 }],
+            errors: [makeError("Function 'a'", 3, 1)]
+        }
     ]
 });