fix(stringToParts): fall back to legacy treatment for square brackets if square brackets contents aren't a number

Re: Automattic/mongoose#9640

Author: vkarpov15

lib/stringToParts.js

@@ -4,28 +4,45 @@ module.exports = function stringToParts(str) {
   const result = [];
 
   let curPropertyName = '';
-  let inSquareBrackets = false;
+  let state = 'DEFAULT';
   for (let i = 0; i < str.length; ++i) {
-    if (inSquareBrackets && !/\d/.test(str[i]) && str[i] !== ']') {
-      throw new Error('Can only use numbers in square bracket path notation, got ' +
-        'character "' + str[i] + '" in path "' + str + '"');
+    // Fall back to treating as property name rather than bracket notation if
+    // square brackets contains something other than a number.
+    if (state === 'IN_SQUARE_BRACKETS' && !/\d/.test(str[i]) && str[i] !== ']') {
+      state = 'DEFAULT';
+      curPropertyName = result[result.length - 1] + '[' + curPropertyName;
+      result.splice(result.length - 1, 1);
     }
 
-    if (str[i] === '.' || str[i] === '[' || str[i] === ']') {
-      if (str[i] === '[') {
-        inSquareBrackets = true;
-      } else if (str[i] === ']') {
-        inSquareBrackets = false;
+    if (str[i] === '[') {
+      if (state !== 'IMMEDIATELY_AFTER_SQUARE_BRACKETS') {
+        result.push(curPropertyName);
+        curPropertyName = '';
+      }
+      state = 'IN_SQUARE_BRACKETS';
+    } else if (str[i] === ']') {
+      if (state === 'IN_SQUARE_BRACKETS') {
+        state = 'IMMEDIATELY_AFTER_SQUARE_BRACKETS';
+        result.push(curPropertyName);
+        curPropertyName = '';
+      } else {
+        state = 'DEFAULT';
+        curPropertyName += str[i];
       }
-      if (curPropertyName.length > 0) {
+    } else if (str[i] === '.') {
+      if (state !== 'IMMEDIATELY_AFTER_SQUARE_BRACKETS') {
         result.push(curPropertyName);
+        curPropertyName = '';
       }
-      curPropertyName = '';
+      state = 'DEFAULT';
     } else {
       curPropertyName += str[i];
     }
   }
-  result.push(curPropertyName);
+
+  if (state !== 'IMMEDIATELY_AFTER_SQUARE_BRACKETS') {
+    result.push(curPropertyName);
+  }
 
   return result;
 };

test/stringToParts.js

@@ -11,11 +11,13 @@ describe('stringToParts', function() {
 
   it('handles dot notation', function() {
     assert.deepEqual(stringToParts('a.b.c'), ['a', 'b', 'c']);
-    assert.deepEqual(stringToParts('a..b.d'), ['a', 'b', 'd']);
+    assert.deepEqual(stringToParts('a..b.d'), ['a', '', 'b', 'd']);
   });
 
-  it('throws for invalid numbers in square brackets', function() {
-    assert.throws(() => stringToParts('foo[1mystring]'), /1mystring/);
+  it('ignores invalid numbers in square brackets', function() {
+    assert.deepEqual(stringToParts('foo[1mystring]'), ['foo[1mystring]']);
+    assert.deepEqual(stringToParts('foo[1mystring].bar[1]'), ['foo[1mystring]', 'bar', '1']);
+    assert.deepEqual(stringToParts('foo[1mystring][2]'), ['foo[1mystring]', '2']);
   });
 
   it('handles empty string', function() {