Fix: prefer-template autofix produces syntax error with octal escapes

lib/rules/prefer-template.js

@@ -52,16 +52,7 @@ function isOctalEscapeSequence(node) {
         return false;
     }
 
-    const match = node.raw.match(/^([^\\]|\\[^0-7])*\\([0-7]{1,3})/u);
-
-    if (match) {
-
-        // \0 is actually not considered an octal
-        if (match[2] !== "0" || typeof match[3] !== "undefined") {
-            return true;
-        }
-    }
-    return false;
+    return astUtils.hasOctalEscapeSequence(node.raw);
 }
 
 /**

lib/rules/utils/ast-utils.js

@@ -38,6 +38,7 @@ const LINEBREAKS = new Set(["\r\n", "\r", "\n", "\u2028", "\u2029"]);
 const STATEMENT_LIST_PARENTS = new Set(["Program", "BlockStatement", "SwitchCase"]);
 
 const DECIMAL_INTEGER_PATTERN = /^(0|[1-9]\d*)$/u;
+const OCTAL_ESCAPE_PATTERN = /^(?:[^\\]|\\[^0-7]|\\0(?![0-9]))*\\(?:[1-7]|0[0-9])/u;
 
 /**
  * Checks reference if is non initializer and writable.
@@ -1373,5 +1374,20 @@ module.exports = {
             "/*".length +
             (match ? match.index + 1 : 0)
         );
+    },
+
+    /**
+     * Determines whether the given raw string contains an octal escape sequence.
+     *
+     * "\1", "\2" ... "\7"
+     * "\00", "\01" ... "\09"
+     *
+     * "\0", when not followed by a digit, is not an octal escape sequence.
+     *
+     * @param {string} rawString A string in its raw representation.
+     * @returns {boolean} `true` if the string contains at least one octal escape sequence.
+     */
+    hasOctalEscapeSequence(rawString) {
+        return OCTAL_ESCAPE_PATTERN.test(rawString);
     }
 };

tests/lib/rules/prefer-template.js

@@ -199,6 +199,16 @@ ruleTester.run("prefer-template", rule, {
             output: null,
             errors
         },
+        {
+            code: "foo + '\\0\\1'",
+            output: null,
+            errors
+        },
+        {
+            code: "foo + '\\08'",
+            output: null,
+            errors
+        },
         {
             code: "foo + '\\\\033'",
             output: "`${foo  }\\\\033`",

tests/lib/rules/utils/ast-utils.js

@@ -1248,4 +1248,82 @@ describe("ast-utils", () => {
             assert.strictEqual(astUtils.equalTokens(ast.body[0], ast.body[1], sourceCode), false);
         });
     });
+
+    describe("hasOctalEscapeSequence", () => {
+
+        /* eslint-disable quote-props */
+        const expectedResults = {
+            "\\1": true,
+            "\\2": true,
+            "\\7": true,
+            "\\00": true,
+            "\\01": true,
+            "\\02": true,
+            "\\07": true,
+            "\\08": true,
+            "\\09": true,
+            "\\10": true,
+            "\\12": true,
+            " \\1": true,
+            "\\1 ": true,
+            "a\\1": true,
+            "\\1a": true,
+            "a\\1a": true,
+            " \\01": true,
+            "\\01 ": true,
+            "a\\01": true,
+            "\\01a": true,
+            "a\\01a": true,
+            "a\\08a": true,
+            "\\0\\1": true,
+            "\\0\\01": true,
+            "\\0\\08": true,
+            "\\n\\1": true,
+            "\\n\\01": true,
+            "\\n\\08": true,
+            "\\\\\\1": true,
+            "\\\\\\01": true,
+            "\\\\\\08": true,
+
+            "\\0": false,
+            "\\8": false,
+            "\\9": false,
+            " \\0": false,
+            "\\0 ": false,
+            "a\\0": false,
+            "\\0a": false,
+            "a\\8a": false,
+            "\\0\\8": false,
+            "\\8\\0": false,
+            "\\80": false,
+            "\\81": false,
+            "\\\\": false,
+            "\\\\0": false,
+            "\\\\01": false,
+            "\\\\08": false,
+            "\\\\1": false,
+            "\\\\12": false,
+            "\\\\\\0": false,
+            "\\\\\\8": false,
+            "\\0\\\\": false,
+            "0": false,
+            "1": false,
+            "8": false,
+            "01": false,
+            "08": false,
+            "80": false,
+            "12": false,
+            "\\a": false,
+            "\\n": false
+        };
+        /* eslint-enable quote-props */
+
+        Object.keys(expectedResults).forEach(key => {
+            it(`should return ${expectedResults[key]} for ${key}`, () => {
+                const ast = espree.parse(`"${key}"`);
+
+                assert.strictEqual(astUtils.hasOctalEscapeSequence(ast.body[0].expression.raw), expectedResults[key]);
+            });
+        });
+    });
 });