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+/*
+ * This file is forked from the handlebars project (https://github.com/handlebars-lang/handlebars.js),
+ * and may include modifications made by Elasticsearch B.V.
+ * Elasticsearch B.V. licenses this file to you under the MIT License.
+ * See `packages/kbn-handlebars/LICENSE` for more information.
+ */
+
+import Handlebars, { type HelperOptions } from '../..';
+import { expectTemplate, forEachCompileFunctionName } from '../__jest__/test_bench';
+
+describe('Regressions', () => {
+  it('GH-94: Cannot read property of undefined', () => {
+    expectTemplate('{{#books}}{{title}}{{author.name}}{{/books}}')
+      .withInput({
+        books: [
+          {
+            title: 'The origin of species',
+            author: {
+              name: 'Charles Darwin',
+            },
+          },
+          {
+            title: 'Lazarillo de Tormes',
+          },
+        ],
+      })
+      .toCompileTo('The origin of speciesCharles DarwinLazarillo de Tormes');
+  });
+
+  it("GH-150: Inverted sections print when they shouldn't", () => {
+    const string = '{{^set}}not set{{/set}} :: {{#set}}set{{/set}}';
+    expectTemplate(string).toCompileTo('not set :: ');
+    expectTemplate(string).withInput({ set: undefined }).toCompileTo('not set :: ');
+    expectTemplate(string).withInput({ set: false }).toCompileTo('not set :: ');
+    expectTemplate(string).withInput({ set: true }).toCompileTo(' :: set');
+  });
+
+  it('GH-158: Using array index twice, breaks the template', () => {
+    expectTemplate('{{arr.[0]}}, {{arr.[1]}}')
+      .withInput({ arr: [1, 2] })
+      .toCompileTo('1, 2');
+  });
+
+  it("bug reported by @fat where lambdas weren't being properly resolved", () => {
+    const string =
+      '<strong>This is a slightly more complicated {{thing}}.</strong>.\n' +
+      '{{! Just ignore this business. }}\n' +
+      'Check this out:\n' +
+      '{{#hasThings}}\n' +
+      '<ul>\n' +
+      '{{#things}}\n' +
+      '<li class={{className}}>{{word}}</li>\n' +
+      '{{/things}}</ul>.\n' +
+      '{{/hasThings}}\n' +
+      '{{^hasThings}}\n' +
+      '\n' +
+      '<small>Nothing to check out...</small>\n' +
+      '{{/hasThings}}';
+
+    const data = {
+      thing() {
+        return 'blah';
+      },
+      things: [
+        { className: 'one', word: '@fat' },
+        { className: 'two', word: '@dhg' },
+        { className: 'three', word: '@sayrer' },
+      ],
+      hasThings() {
+        return true;
+      },
+    };
+
+    const output =
+      '<strong>This is a slightly more complicated blah.</strong>.\n' +
+      'Check this out:\n' +
+      '<ul>\n' +
+      '<li class=one>@fat</li>\n' +
+      '<li class=two>@dhg</li>\n' +
+      '<li class=three>@sayrer</li>\n' +
+      '</ul>.\n';
+
+    expectTemplate(string).withInput(data).toCompileTo(output);
+  });
+
+  it('GH-408: Multiple loops fail', () => {
+    expectTemplate('{{#.}}{{name}}{{/.}}{{#.}}{{name}}{{/.}}{{#.}}{{name}}{{/.}}')
+      .withInput([
+        { name: 'John Doe', location: { city: 'Chicago' } },
+        { name: 'Jane Doe', location: { city: 'New York' } },
+      ])
+      .toCompileTo('John DoeJane DoeJohn DoeJane DoeJohn DoeJane Doe');
+  });
+
+  it('GS-428: Nested if else rendering', () => {
+    const succeedingTemplate =
+      '{{#inverse}} {{#blk}} Unexpected {{/blk}} {{else}}  {{#blk}} Expected {{/blk}} {{/inverse}}';
+    const failingTemplate =
+      '{{#inverse}} {{#blk}} Unexpected {{/blk}} {{else}} {{#blk}} Expected {{/blk}} {{/inverse}}';
+
+    const helpers = {
+      blk(block: HelperOptions) {
+        return block.fn('');
+      },
+      inverse(block: HelperOptions) {
+        return block.inverse('');
+      },
+    };
+
+    expectTemplate(succeedingTemplate).withHelpers(helpers).toCompileTo('   Expected  ');
+    expectTemplate(failingTemplate).withHelpers(helpers).toCompileTo('  Expected  ');
+  });
+
+  it('GH-458: Scoped this identifier', () => {
+    expectTemplate('{{./foo}}').withInput({ foo: 'bar' }).toCompileTo('bar');
+  });
+
+  it('GH-375: Unicode line terminators', () => {
+    expectTemplate('\u2028').toCompileTo('\u2028');
+  });
+
+  it('GH-534: Object prototype aliases', () => {
+    /* eslint-disable no-extend-native */
+    // @ts-expect-error
+    Object.prototype[0xd834] = true;
+
+    expectTemplate('{{foo}}').withInput({ foo: 'bar' }).toCompileTo('bar');
+
+    // @ts-expect-error
+    delete Object.prototype[0xd834];
+    /* eslint-enable no-extend-native */
+  });
+
+  it('GH-437: Matching escaping', () => {
+    expectTemplate('{{{a}}').toThrow(/Parse error on/);
+    expectTemplate('{{a}}}').toThrow(/Parse error on/);
+  });
+
+  it('GH-676: Using array in escaping mustache fails', () => {
+    const data = { arr: [1, 2] };
+    expectTemplate('{{arr}}').withInput(data).toCompileTo(data.arr.toString());
+  });
+
+  it('Mustache man page', () => {
+    expectTemplate(
+      'Hello {{name}}. You have just won ${{value}}!{{#in_ca}} Well, ${{taxed_value}}, after taxes.{{/in_ca}}'
+    )
+      .withInput({
+        name: 'Chris',
+        value: 10000,
+        taxed_value: 10000 - 10000 * 0.4,
+        in_ca: true,
+      })
+      .toCompileTo('Hello Chris. You have just won $10000! Well, $6000, after taxes.');
+  });
+
+  it('GH-731: zero context rendering', () => {
+    expectTemplate('{{#foo}} This is {{bar}} ~ {{/foo}}')
+      .withInput({
+        foo: 0,
+        bar: 'OK',
+      })
+      .toCompileTo(' This is  ~ ');
+  });
+
+  it('GH-820: zero pathed rendering', () => {
+    expectTemplate('{{foo.bar}}').withInput({ foo: 0 }).toCompileTo('');
+  });
+
+  it('GH-837: undefined values for helpers', () => {
+    expectTemplate('{{str bar.baz}}')
+      .withHelpers({
+        str(value) {
+          return value + '';
+        },
+      })
+      .toCompileTo('undefined');
+  });
+
+  it('GH-926: Depths and de-dupe', () => {
+    expectTemplate(
+      '{{#if dater}}{{#each data}}{{../name}}{{/each}}{{else}}{{#each notData}}{{../name}}{{/each}}{{/if}}'
+    )
+      .withInput({
+        name: 'foo',
+        data: [1],
+        notData: [1],
+      })
+      .toCompileTo('foo');
+  });
+
+  it('GH-1021: Each empty string key', () => {
+    expectTemplate('{{#each data}}Key: {{@key}}\n{{/each}}')
+      .withInput({
+        data: {
+          '': 'foo',
+          name: 'Chris',
+          value: 10000,
+        },
+      })
+      .toCompileTo('Key: \nKey: name\nKey: value\n');
+  });
+
+  it('GH-1054: Should handle simple safe string responses', () => {
+    expectTemplate('{{#wrap}}{{>partial}}{{/wrap}}')
+      .withHelpers({
+        wrap(options: HelperOptions) {
+          return new Handlebars.SafeString(options.fn());
+        },
+      })
+      .withPartials({
+        partial: '{{#wrap}}<partial>{{/wrap}}',
+      })
+      .toCompileTo('<partial>');
+  });
+
+  it('GH-1065: Sparse arrays', () => {
+    const array = [];
+    array[1] = 'foo';
+    array[3] = 'bar';
+    expectTemplate('{{#each array}}{{@index}}{{.}}{{/each}}')
+      .withInput({ array })
+      .toCompileTo('1foo3bar');
+  });
+
+  it('GH-1093: Undefined helper context', () => {
+    expectTemplate('{{#each obj}}{{{helper}}}{{.}}{{/each}}')
+      .withInput({ obj: { foo: undefined, bar: 'bat' } })
+      .withHelpers({
+        helper(this: any) {
+          // It's valid to execute a block against an undefined context, but
+          // helpers can not do so, so we expect to have an empty object here;
+          for (const name in this) {
+            if (Object.prototype.hasOwnProperty.call(this, name)) {
+              return 'found';
+            }
+          }
+          // And to make IE happy, check for the known string as length is not enumerated.
+          return this === 'bat' ? 'found' : 'not';
+        },
+      })
+      .toCompileTo('notfoundbat');
+  });
+
+  it('should support multiple levels of inline partials', () => {
+    expectTemplate('{{#> layout}}{{#*inline "subcontent"}}subcontent{{/inline}}{{/layout}}')
+      .withPartials({
+        doctype: 'doctype{{> content}}',
+        layout: '{{#> doctype}}{{#*inline "content"}}layout{{> subcontent}}{{/inline}}{{/doctype}}',
+      })
+      .toCompileTo('doctypelayoutsubcontent');
+  });
+
+  it('GH-1089: should support failover content in multiple levels of inline partials', () => {
+    expectTemplate('{{#> layout}}{{/layout}}')
+      .withPartials({
+        doctype: 'doctype{{> content}}',
+        layout:
+          '{{#> doctype}}{{#*inline "content"}}layout{{#> subcontent}}subcontent{{/subcontent}}{{/inline}}{{/doctype}}',
+      })
+      .toCompileTo('doctypelayoutsubcontent');
+  });
+
+  it('GH-1099: should support greater than 3 nested levels of inline partials', () => {
+    expectTemplate('{{#> layout}}Outer{{/layout}}')
+      .withPartials({
+        layout: '{{#> inner}}Inner{{/inner}}{{> @partial-block }}',
+        inner: '',
+      })
+      .toCompileTo('Outer');
+  });
+
+  it('GH-1135 : Context handling within each iteration', () => {
+    expectTemplate(
+      '{{#each array}}\n' +
+        ' 1. IF: {{#if true}}{{../name}}-{{../../name}}-{{../../../name}}{{/if}}\n' +
+        ' 2. MYIF: {{#myif true}}{{../name}}={{../../name}}={{../../../name}}{{/myif}}\n' +
+        '{{/each}}'
+    )
+      .withInput({ array: [1], name: 'John' })
+      .withHelpers({
+        myif(conditional, options: HelperOptions) {
+          if (conditional) {
+            return options.fn(this);
+          } else {
+            return options.inverse(this);
+          }
+        },
+      })
+      .toCompileTo(' 1. IF: John--\n' + ' 2. MYIF: John==\n');
+  });
+
+  it('GH-1186: Support block params for existing programs', () => {
+    expectTemplate(
+      '{{#*inline "test"}}{{> @partial-block }}{{/inline}}' +
+        '{{#>test }}{{#each listOne as |item|}}{{ item }}{{/each}}{{/test}}' +
+        '{{#>test }}{{#each listTwo as |item|}}{{ item }}{{/each}}{{/test}}'
+    )
+      .withInput({
+        listOne: ['a'],
+        listTwo: ['b'],
+      })
+      .toCompileTo('ab');
+  });
+
+  it('GH-1319: "unless" breaks when "each" value equals "null"', () => {
+    expectTemplate('{{#each list}}{{#unless ./prop}}parent={{../value}} {{/unless}}{{/each}}')
+      .withInput({
+        value: 'parent',
+        list: [null, 'a'],
+      })
+      .toCompileTo('parent=parent parent=parent ');
+  });
+
+  it('GH-1341: 4.0.7 release breaks {{#if @partial-block}} usage', () => {
+    expectTemplate('template {{>partial}} template')
+      .withPartials({
+        partialWithBlock: '{{#if @partial-block}} block {{> @partial-block}} block {{/if}}',
+        partial: '{{#> partialWithBlock}} partial {{/partialWithBlock}}',
+      })
+      .toCompileTo('template  block  partial  block  template');
+  });
+
+  it('should allow hash with protected array names', () => {
+    expectTemplate('{{helpa length="foo"}}')
+      .withInput({ array: [1], name: 'John' })
+      .withHelpers({
+        helpa(options: HelperOptions) {
+          return options.hash.length;
+        },
+      })
+      .toCompileTo('foo');
+  });
+
+  describe('GH-1598: Performance degradation for partials since v4.3.0', () => {
+    let newHandlebarsInstance: typeof Handlebars;
+    let spy: jest.SpyInstance;
+    beforeEach(() => {
+      newHandlebarsInstance = Handlebars.create();
+    });
+    afterEach(() => {
+      spy.mockRestore();
+    });
+
+    forEachCompileFunctionName((compileName) => {
+      it(`should only compile global partials once when calling #${compileName}`, () => {
+        const compile = newHandlebarsInstance[compileName].bind(newHandlebarsInstance);
+        let calls;
+        switch (compileName) {
+          case 'compile':
+            spy = jest.spyOn(newHandlebarsInstance, 'template');
+            calls = 3;
+            break;
+          case 'compileAST':
+            spy = jest.spyOn(newHandlebarsInstance, 'compileAST');
+            calls = 2;
+            break;
+        }
+        newHandlebarsInstance.registerPartial({
+          dude: 'I am a partial',
+        });
+        const string = 'Dudes: {{> dude}} {{> dude}}';
+        compile(string)(); // This should compile template + partial once
+        compile(string)(); // This should only compile template
+        expect(spy).toHaveBeenCalledTimes(calls);
+        spy.mockRestore();
+      });
+    });
+  });
+
+  describe("GH-1639: TypeError: Cannot read property 'apply' of undefined\" when handlebars version > 4.6.0 (undocumented, deprecated usage)", () => {
+    it('should treat undefined helpers like non-existing helpers', () => {
+      expectTemplate('{{foo}}')
+        .withHelper('foo', undefined as any)
+        .withInput({ foo: 'bar' })
+        .toCompileTo('bar');
+    });
+  });
+});