Fix: no-implicit-coercion string concat false positive (fixes #7057)

lib/rules/no-implicit-coercion.js

@@ -105,15 +105,35 @@ function getNonNumericOperand(node) {
     return null;
 }
 
+/**
+ * Checks whether a node is a string literal or not.
+ * @param {ASTNode} node The node to check.
+ * @returns {boolean} Whether or not the passed in node is a
+ * string literal or not.
+ */
+function isString(node) {
+  return node.type === "Literal" && typeof node.value === "string";
+}
+
+/**
+ * Checks whether a node is an empty string literal or not.
+ * @param {ASTNode} node The node to check.
+ * @returns {boolean} Whether or not the passed in node is an
+ * empty string literal or not.
+ */
+function isEmptyString(node) {
+  return isString(node) && node.value === "";
+}
+
 /**
  * Checks whether or not a node is a concatenating with an empty string.
  * @param {ASTNode} node - A BinaryExpression node to check.
  * @returns {boolean} Whether or not the node is a concatenating with an empty string.
  */
 function isConcatWithEmptyString(node) {
     return node.operator === "+" && (
-        (node.left.type === "Literal" && node.left.value === "") ||
-        (node.right.type === "Literal" && node.right.value === "")
+        (isEmptyString(node.left) && !isString(node.right)) ||
+        (isEmptyString(node.right) && !isString(node.left))
     );
 }
 
@@ -123,7 +143,7 @@ function isConcatWithEmptyString(node) {
  * @returns {boolean} Whether or not the node is appended with an empty string.
  */
 function isAppendEmptyString(node) {
-    return node.operator === "+=" && node.right.type === "Literal" && node.right.value === "";
+    return node.operator === "+=" && isEmptyString(node.right);
 }
 
 /**

tests/lib/rules/no-implicit-coercion.js

@@ -64,6 +64,10 @@ ruleTester.run("no-implicit-coercion", rule, {
         {code: "0 + foo"},
         {code: "~foo.bar()"},
 
+        // https://github.com/eslint/eslint/issues/7057
+        {code: "'' + 'foo'"},
+        {code: "+42"},
+
         {code: "!!foo", options: [{boolean: false}]},
         {code: "~foo.indexOf(1)", options: [{boolean: false}]},
         {code: "+foo", options: [{number: false}]},