⚒ improve no-path-concat

Author: mysticatea

Diff for: docs/rules/no-path-concat.md

@@ -30,20 +30,25 @@ This rule aims to prevent string concatenation of directory paths in Node.js
 Examples of **incorrect** code for this rule:
 
 ```js
-/*eslint no-path-concat: "error"*/
-
-var fullPath = __dirname + "/foo.js";
-
-var fullPath = __filename + "/foo.js";
+/*eslint node/no-path-concat: "error"*/
 
+const fullPath1 = __dirname + "/foo.js";
+const fullPath2 = __filename + "/foo.js";
+const fullPath3 = `${__dirname}/foo.js`;
+const fullPath4 = `${__filename}/foo.js`;
 ```
 
 Examples of **correct** code for this rule:
 
 ```js
-/*eslint no-path-concat: "error"*/
-
-var fullPath = dirname + "/foo.js";
+/*eslint node/no-path-concat: "error"*/
+
+const fullPath1 = path.join(__dirname, "foo.js");
+const fullPath2 = path.join(__filename, "foo.js");
+const fullPath3 = __dirname + ".js";
+const fullPath4 = __filename + ".map";
+const fullPath5 = `${__dirname}_foo.js`;
+const fullPath6 = `${__filename}.test.js`;
 ```
 
 ## 🔎 Implementation

Diff for: lib/rules/no-path-concat.js

@@ -4,6 +4,158 @@
  */
 "use strict"
 
+const path = require("path")
+const { READ, ReferenceTracker, getStringIfConstant } = require("eslint-utils")
+
+/**
+ * Get the first char of the specified template element.
+ * @param {TemplateLiteral} node The `TemplateLiteral` node to get.
+ * @param {number} i The number of template elements to get first char.
+ * @param {Set<Node>} sepNodes The nodes of `path.sep`.
+ * @param {import("escope").Scope} globalScope The global scope object.
+ * @param {string[]} outNextChars The array to collect chars.
+ * @returns {void}
+ */
+function collectFirstCharsOfTemplateElement(
+    node,
+    i,
+    sepNodes,
+    globalScope,
+    outNextChars
+) {
+    const element = node.quasis[i].value.cooked
+
+    if (element == null) {
+        return
+    }
+    if (element !== "") {
+        outNextChars.push(element[0])
+        return
+    }
+    if (node.expressions.length > i) {
+        collectFirstChars(
+            node.expressions[i],
+            sepNodes,
+            globalScope,
+            outNextChars
+        )
+    }
+}
+
+/**
+ * Get the first char of a given node.
+ * @param {TemplateLiteral} node The `TemplateLiteral` node to get.
+ * @param {Set<Node>} sepNodes The nodes of `path.sep`.
+ * @param {import("escope").Scope} globalScope The global scope object.
+ * @param {string[]} outNextChars The array to collect chars.
+ * @returns {void}
+ */
+function collectFirstChars(node, sepNodes, globalScope, outNextChars) {
+    switch (node.type) {
+        case "AssignmentExpression":
+            collectFirstChars(node.right, sepNodes, globalScope, outNextChars)
+            break
+        case "BinaryExpression":
+            collectFirstChars(node.left, sepNodes, globalScope, outNextChars)
+            break
+        case "ConditionalExpression":
+            collectFirstChars(
+                node.consequent,
+                sepNodes,
+                globalScope,
+                outNextChars
+            )
+            collectFirstChars(
+                node.alternate,
+                sepNodes,
+                globalScope,
+                outNextChars
+            )
+            break
+        case "LogicalExpression":
+            collectFirstChars(node.left, sepNodes, globalScope, outNextChars)
+            collectFirstChars(node.right, sepNodes, globalScope, outNextChars)
+            break
+        case "SequenceExpression":
+            collectFirstChars(
+                node.expressions[node.expressions.length - 1],
+                sepNodes,
+                globalScope,
+                outNextChars
+            )
+            break
+        case "TemplateLiteral":
+            collectFirstCharsOfTemplateElement(
+                node,
+                0,
+                sepNodes,
+                globalScope,
+                outNextChars
+            )
+            break
+
+        case "Identifier":
+        case "MemberExpression":
+            if (sepNodes.has(node)) {
+                outNextChars.push(path.sep)
+                break
+            }
+        // fallthrough
+        default: {
+            const str = getStringIfConstant(node, globalScope)
+            if (str) {
+                outNextChars.push(str[0])
+            }
+        }
+    }
+}
+
+/**
+ * Check if a char is a path separator or not.
+ * @param {string} c The char to check.
+ * @returns {boolean} `true` if the char is a path separator.
+ */
+function isPathSeparator(c) {
+    return c === "/" || c === path.sep
+}
+
+/**
+ * Check if the given Identifier node is followed by string concatenation with a
+ * path separator.
+ * @param {Identifier} node The `__dirname` or `__filename` node to check.
+ * @param {Set<Node>} sepNodes The nodes of `path.sep`.
+ * @param {import("escope").Scope} globalScope The global scope object.
+ * @returns {boolean} `true` if the given Identifier node is followed by string
+ * concatenation with a path separator.
+ */
+function isConcat(node, sepNodes, globalScope) {
+    const parent = node.parent
+    const nextChars = []
+
+    if (
+        parent.type === "BinaryExpression" &&
+        parent.operator === "+" &&
+        parent.left === node
+    ) {
+        collectFirstChars(
+            parent.right,
+            sepNodes,
+            globalScope,
+            /* out */ nextChars
+        )
+    } else if (parent.type === "TemplateLiteral") {
+        collectFirstCharsOfTemplateElement(
+            parent,
+            parent.expressions.indexOf(node) + 1,
+            sepNodes,
+            globalScope,
+            /* out */ nextChars
+        )
+    }
+
+    return nextChars.some(isPathSeparator)
+}
+
 module.exports = {
     meta: {
         type: "suggestion",
@@ -19,28 +171,40 @@ module.exports = {
         schema: [],
         messages: {
             usePathFunctions:
-                "Use path.join() or path.resolve() instead of + to create paths.",
+                "Use path.join() or path.resolve() instead of string concatenation.",
         },
     },
 
     create(context) {
-        const MATCHER = /^__(?:dir|file)name$/u
-
         return {
-            BinaryExpression(node) {
-                const left = node.left
-                const right = node.right
-
-                if (
-                    node.operator === "+" &&
-                    ((left.type === "Identifier" && MATCHER.test(left.name)) ||
-                        (right.type === "Identifier" &&
-                            MATCHER.test(right.name)))
-                ) {
-                    context.report({
-                        node,
-                        messageId: "usePathFunctions",
-                    })
+            "Program:exit"() {
+                const globalScope = context.getScope()
+                const tracker = new ReferenceTracker(globalScope)
+                const sepNodes = new Set()
+
+                // Collect `paht.sep` references
+                for (const { node } of tracker.iterateCjsReferences({
+                    path: { sep: { [READ]: true } },
+                })) {
+                    sepNodes.add(node)
+                }
+                for (const { node } of tracker.iterateEsmReferences({
+                    path: { sep: { [READ]: true } },
+                })) {
+                    sepNodes.add(node)
+                }
+
+                // Verify `__dirname` and `__filename`
+                for (const { node } of tracker.iterateGlobalReferences({
+                    __dirname: { [READ]: true },
+                    __filename: { [READ]: true },
+                })) {
+                    if (isConcat(node, sepNodes, globalScope)) {
+                        context.report({
+                            node: node.parent,
+                            messageId: "usePathFunctions",
+                        })
+                    }
                 }
             },
         }