From 7f86df81899e2b12b70bd66790d8d15abc490b06 Mon Sep 17 00:00:00 2001
From: Milos Djermanovic <milos.djermanovic@gmail.com>
Date: Fri, 27 Aug 2021 14:39:23 +0200
Subject: [PATCH] Use code path analysis

---
 lib/rules/complexity.js | 130 +++++++++++++++-------------------------
 1 file changed, 48 insertions(+), 82 deletions(-)

diff --git a/lib/rules/complexity.js b/lib/rules/complexity.js
index ebf24e10adf..377c54a0291 100644
--- a/lib/rules/complexity.js
+++ b/lib/rules/complexity.js
@@ -74,73 +74,16 @@ module.exports = {
         // Helpers
         //--------------------------------------------------------------------------
 
-        // Using a stack to store complexity (handling nested functions)
-        const fns = [];
+        // Using a stack to store complexity per code path
+        const complexities = [];
 
         /**
-         * When parsing a new function, store it in our function stack
-         * @returns {void}
-         * @private
-         */
-        function startFunction() {
-            fns.push(1);
-        }
-
-        /**
-         * Evaluate the node at the end of function
-         * @param {ASTNode} node node to evaluate. If it is a `PropertyDefinition` node, its initializer is being evaluated.
-         * @returns {void}
-         * @private
-         */
-        function endFunction(node) {
-            const complexity = fns.pop();
-
-            if (complexity > THRESHOLD) {
-                let evaluatedNode, name;
-
-                if (node.type === "PropertyDefinition") {
-                    evaluatedNode = node.value;
-                    name = "class field initializer";
-                } else {
-                    evaluatedNode = node;
-                    name = astUtils.getFunctionNameWithKind(node);
-                }
-
-                context.report({
-                    node: evaluatedNode,
-                    messageId: "complex",
-                    data: {
-                        name: upperCaseFirst(name),
-                        complexity,
-                        max: THRESHOLD
-                    }
-                });
-            }
-        }
-
-        /**
-         * Increase the complexity of the function in context
+         * Increase the complexity of the code path in context
          * @returns {void}
          * @private
          */
         function increaseComplexity() {
-            if (fns.length) {
-                fns[fns.length - 1]++;
-            }
-        }
-
-        /**
-         * Increase the switch complexity in context
-         * @param {ASTNode} node node to evaluate
-         * @returns {void}
-         * @private
-         */
-        function increaseSwitchComplexity(node) {
-
-            // Avoiding `default`
-            if (node.test) {
-                increaseComplexity();
-            }
+            complexities[complexities.length - 1]++;
         }
 
         //--------------------------------------------------------------------------
@@ -148,27 +91,14 @@ module.exports = {
         //--------------------------------------------------------------------------
 
         return {
-            FunctionDeclaration: startFunction,
-            FunctionExpression: startFunction,
-            ArrowFunctionExpression: startFunction,
-            "FunctionDeclaration:exit": endFunction,
-            "FunctionExpression:exit": endFunction,
-            "ArrowFunctionExpression:exit": endFunction,
-
-            /*
-             * Class field initializers are implicit functions. Therefore, they shouldn't contribute
-             * to the enclosing function's complexity, but their own complexity should be evaluated.
-             * We're using `*.key:exit` here in order to make sure that `startFunction()` is called
-             * before entering the `.value` node, and thus certainly before other listeners
-             * (e.g., if the initializer is `a || b`, due to a higher selector specificity
-             * `PropertyDefinition > *.value` would be called after `LogicalExpression`).
-             * We're passing the `PropertyDefinition` node instead of `PropertyDefinition.value` node
-             * to `endFunction(node)` in order to disambiguate between evaluating implicit initializer
-             * functions and "regular" functions, which may be the `.value` itself, e.g., `x = () => {};`.
-             */
-            "PropertyDefinition[value] > *.key:exit": startFunction,
-            "PropertyDefinition[value]:exit": endFunction,
 
+            onCodePathStart() {
+
+                // The initial complexity is 1, representing one execution path in the CodePath
+                complexities.push(1);
+            },
+
+            // Each branching in the code adds 1 to the complexity
             CatchClause: increaseComplexity,
             ConditionalExpression: increaseComplexity,
             LogicalExpression: increaseComplexity,
@@ -176,14 +106,50 @@ module.exports = {
             ForInStatement: increaseComplexity,
             ForOfStatement: increaseComplexity,
             IfStatement: increaseComplexity,
-            SwitchCase: increaseSwitchComplexity,
             WhileStatement: increaseComplexity,
             DoWhileStatement: increaseComplexity,
 
+            // Avoid `default`
+            "SwitchCase[test]": increaseComplexity,
+
+            // Logical assignment operators have short-circuiting behavior
             AssignmentExpression(node) {
                 if (astUtils.isLogicalAssignmentOperator(node.operator)) {
                     increaseComplexity();
                 }
+            },
+
+            onCodePathEnd(codePath, node) {
+                const complexity = complexities.pop();
+
+                /*
+                 * This rule only evaluates complexity of functions, so "program" is excluded.
+                 * Class field initializers are implicit functions. Therefore, they shouldn't contribute
+                 * to the enclosing function's complexity, but their own complexity should be evaluated.
+                 */
+                if (
+                    codePath.origin !== "function" &&
+                    codePath.origin !== "class-field-initializer"
+                ) {
+                    return;
+                }
+
+
+                if (complexity > THRESHOLD) {
+                    const name = codePath.origin === "class-field-initializer"
+                        ? "class field initializer"
+                        : astUtils.getFunctionNameWithKind(node);
+
+                    context.report({
+                        node,
+                        messageId: "complex",
+                        data: {
+                            name: upperCaseFirst(name),
+                            complexity,
+                            max: THRESHOLD
+                        }
+                    });
+                }
             }
         };