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app_vue/node_modules/eslint/lib/rules/no-useless-concat.js

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+/**
+ * @fileoverview disallow unnecessary concatenation of template strings
+ * @author Henry Zhu
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const astUtils = require("./utils/ast-utils");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Checks whether or not a given node is a concatenation.
+ * @param {ASTNode} node A node to check.
+ * @returns {boolean} `true` if the node is a concatenation.
+ */
+function isConcatenation(node) {
+    return node.type === "BinaryExpression" && node.operator === "+";
+}
+
+/**
+ * Checks if the given token is a `+` token or not.
+ * @param {Token} token The token to check.
+ * @returns {boolean} `true` if the token is a `+` token.
+ */
+function isConcatOperatorToken(token) {
+    return token.value === "+" && token.type === "Punctuator";
+}
+
+/**
+ * Get's the right most node on the left side of a BinaryExpression with + operator.
+ * @param {ASTNode} node A BinaryExpression node to check.
+ * @returns {ASTNode} node
+ */
+function getLeft(node) {
+    let left = node.left;
+
+    while (isConcatenation(left)) {
+        left = left.right;
+    }
+    return left;
+}
+
+/**
+ * Get's the left most node on the right side of a BinaryExpression with + operator.
+ * @param {ASTNode} node A BinaryExpression node to check.
+ * @returns {ASTNode} node
+ */
+function getRight(node) {
+    let right = node.right;
+
+    while (isConcatenation(right)) {
+        right = right.left;
+    }
+    return right;
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "disallow unnecessary concatenation of literals or template literals",
+            category: "Best Practices",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/no-useless-concat"
+        },
+
+        schema: [],
+
+        messages: {
+            unexpectedConcat: "Unexpected string concatenation of literals."
+        }
+    },
+
+    create(context) {
+        const sourceCode = context.getSourceCode();
+
+        return {
+            BinaryExpression(node) {
+
+                // check if not concatenation
+                if (node.operator !== "+") {
+                    return;
+                }
+
+                // account for the `foo + "a" + "b"` case
+                const left = getLeft(node);
+                const right = getRight(node);
+
+                if (astUtils.isStringLiteral(left) &&
+                    astUtils.isStringLiteral(right) &&
+                    astUtils.isTokenOnSameLine(left, right)
+                ) {
+                    const operatorToken = sourceCode.getFirstTokenBetween(left, right, isConcatOperatorToken);
+
+                    context.report({
+                        node,
+                        loc: operatorToken.loc,
+                        messageId: "unexpectedConcat"
+                    });
+                }
+            }
+        };
+    }
+};