Fix: no-implicit-coercion invalid autofix with consecutive identifiers (#8340)

Previously, the no-implicit-coercion rule would convert code like `typeof+foo` to `typeofNumber(foo)`, combining the `typeof` keyword with the following identifier and changing the semantics. This commit updates the no-implicit-coercion autofixer to prevent that from happening.

Author: not-an-aardvark

lib/rules/no-implicit-coercion.js

@@ -6,6 +6,7 @@
 "use strict";
 
 const astUtils = require("../ast-utils");
+const esUtils = require("esutils");
 
 //------------------------------------------------------------------------------
 // Helpers
@@ -197,19 +198,31 @@ module.exports = {
         */
         function report(node, recommendation, shouldFix) {
             shouldFix = typeof shouldFix === "undefined" ? true : shouldFix;
-            const reportObj = {
+
+            context.report({
                 node,
                 message: "use `{{recommendation}}` instead.",
                 data: {
                     recommendation
+                },
+                fix(fixer) {
+                    if (!shouldFix) {
+                        return null;
+                    }
+
+                    const tokenBefore = sourceCode.getTokenBefore(node);
+
+                    if (
+                        tokenBefore &&
+                        tokenBefore.range[1] === node.range[0] &&
+                        esUtils.code.isIdentifierPartES6(tokenBefore.value.slice(-1).charCodeAt(0)) &&
+                        esUtils.code.isIdentifierPartES6(recommendation.charCodeAt(0))
+                    ) {
+                        return fixer.replaceText(node, ` ${recommendation}`);
+                    }
+                    return fixer.replaceText(node, recommendation);
                 }
-            };
-
-            if (shouldFix) {
-                reportObj.fix = fixer => fixer.replaceText(node, recommendation);
-            }
-
-            context.report(reportObj);
+            });
         }
 
         return {

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

@@ -221,6 +221,16 @@ ruleTester.run("no-implicit-coercion", rule, {
             parserOptions: { ecmaVersion: 6 },
             errors: [{ message: "use `String(foo)` instead.", type: "BinaryExpression" }],
             output: "var a = String(foo)"
+        },
+        {
+            code: "typeof+foo",
+            output: "typeof Number(foo)",
+            errors: [{ message: "use `Number(foo)` instead.", type: "UnaryExpression" }]
+        },
+        {
+            code: "typeof +foo",
+            output: "typeof Number(foo)",
+            errors: [{ message: "use `Number(foo)` instead.", type: "UnaryExpression" }]
         }
     ]
 });