From d6411c27291b69f46b3b7f648d3445c9c4ba3a4a Mon Sep 17 00:00:00 2001
From: Daniel Trevino <23410540+danieltre23@users.noreply.github.com>
Date: Mon, 26 Jul 2021 18:21:46 +0000
Subject: [PATCH] refactor(compiler-cli): add `BananaInBoxCheck` to the
 template checks (#42984)

Add the implementation of a Template Check that ensures the correct
use of two-way binding syntax. Generates a warning when
'([foo])="bar"' is found instead of '[(foo)]="bar"'.

Refs #42966

PR Close #42984
---
 goldens/public-api/compiler-cli/error_code.md |  2 +-
 .../src/ngtsc/diagnostics/src/error_code.ts   | 10 +++
 .../invalid_banana_in_box/BUILD.bazel         | 13 ++++
 .../invalid_banana_in_box/index.ts            | 65 +++++++++++++++++++
 4 files changed, 89 insertions(+), 1 deletion(-)
 create mode 100644 packages/compiler-cli/src/ngtsc/typecheck/extended/src/template_checks/invalid_banana_in_box/BUILD.bazel
 create mode 100644 packages/compiler-cli/src/ngtsc/typecheck/extended/src/template_checks/invalid_banana_in_box/index.ts

diff --git a/goldens/public-api/compiler-cli/error_code.md b/goldens/public-api/compiler-cli/error_code.md
index 84a4a59516..7134a7b404 100644
--- a/goldens/public-api/compiler-cli/error_code.md
+++ b/goldens/public-api/compiler-cli/error_code.md
@@ -34,6 +34,7 @@ export enum ErrorCode {
     INJECTABLE_DUPLICATE_PROV = 9001,
     INLINE_TCB_REQUIRED = 8900,
     INLINE_TYPE_CTOR_REQUIRED = 8901,
+    INVALID_BANANA_IN_BOX = 8101,
     MISSING_PIPE = 8004,
     MISSING_REFERENCE_TARGET = 8003,
     NGMODULE_DECLARATION_NOT_UNIQUE = 6007,
@@ -67,7 +68,6 @@ export enum ErrorCode {
     WRITE_TO_READ_ONLY_VARIABLE = 8005
 }
 
-
 // (No @packageDocumentation comment for this package)
 
 ```
diff --git a/packages/compiler-cli/src/ngtsc/diagnostics/src/error_code.ts b/packages/compiler-cli/src/ngtsc/diagnostics/src/error_code.ts
index e6dba314c2..26c5ffd587 100644
--- a/packages/compiler-cli/src/ngtsc/diagnostics/src/error_code.ts
+++ b/packages/compiler-cli/src/ngtsc/diagnostics/src/error_code.ts
@@ -172,6 +172,16 @@ export enum ErrorCode {
    */
   SPLIT_TWO_WAY_BINDING = 8007,
 
+  /**
+   * A two way binding in a template has an incorrect syntax,
+   * parentheses outside brackets. For example:
+   *
+   * ```
+   * <div ([foo])="bar" />
+   * ```
+   */
+  INVALID_BANANA_IN_BOX = 8101,
+
   /**
    * The template type-checking engine would need to generate an inline type check block for a
    * component, but the current type-checking environment doesn't support it.
diff --git a/packages/compiler-cli/src/ngtsc/typecheck/extended/src/template_checks/invalid_banana_in_box/BUILD.bazel b/packages/compiler-cli/src/ngtsc/typecheck/extended/src/template_checks/invalid_banana_in_box/BUILD.bazel
new file mode 100644
index 0000000000..f2a1359185
--- /dev/null
+++ b/packages/compiler-cli/src/ngtsc/typecheck/extended/src/template_checks/invalid_banana_in_box/BUILD.bazel
@@ -0,0 +1,13 @@
+load("//tools:defaults.bzl", "ts_library")
+
+ts_library(
+    name = "invalid_banana_in_box",
+    srcs = ["index.ts"],
+    visibility = ["//packages/compiler-cli/src/ngtsc/typecheck/extended:__subpackages__"],
+    deps = [
+        "//packages/compiler",
+        "//packages/compiler-cli/src/ngtsc/diagnostics",
+        "//packages/compiler-cli/src/ngtsc/typecheck/extended/api",
+        "@npm//typescript",
+    ],
+)
diff --git a/packages/compiler-cli/src/ngtsc/typecheck/extended/src/template_checks/invalid_banana_in_box/index.ts b/packages/compiler-cli/src/ngtsc/typecheck/extended/src/template_checks/invalid_banana_in_box/index.ts
new file mode 100644
index 0000000000..93ae48b89b
--- /dev/null
+++ b/packages/compiler-cli/src/ngtsc/typecheck/extended/src/template_checks/invalid_banana_in_box/index.ts
@@ -0,0 +1,65 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {TmplAstBoundEvent, TmplAstNode, TmplAstRecursiveVisitor} from '@angular/compiler';
+import * as ts from 'typescript';
+import {ErrorCode} from '../../../../../diagnostics';
+import {TemplateCheck, TemplateContext, TemplateDiagnostic} from '../../../api/api';
+
+/**
+ * Ensures the two-way binding syntax is correct.
+ * Parentheses should be inside the brackets "[()]".
+ * Will return diagnostic information when "([])" is found.
+ */
+export class InvalidBananaInBoxCheck implements TemplateCheck<ErrorCode.INVALID_BANANA_IN_BOX> {
+  code: ErrorCode.INVALID_BANANA_IN_BOX = 8101;
+
+  run(ctx: TemplateContext,
+      template: TmplAstNode[]): TemplateDiagnostic<ErrorCode.INVALID_BANANA_IN_BOX>[] {
+    const visitor = new BananaVisitor(ctx);
+
+    return visitor.getDiagnostics(template);
+  }
+}
+
+class BananaVisitor extends TmplAstRecursiveVisitor {
+  private diagnostics: ts.Diagnostic[] = [];
+
+  constructor(public readonly ctx: TemplateContext) {
+    super();
+  }
+
+  /**
+   * Check for outputs with names surrounded in brackets "[]".
+   * The syntax '([foo])="bar"' would be interpreted as an @Output()
+   * with name '[foo]'. Just like '(foo)="bar"' would have the name 'foo'.
+   * Generate diagnostic information for the cases found.
+   */
+  override visitBoundEvent(boundEvent: TmplAstBoundEvent) {
+    const name = boundEvent.name;
+    if (name.startsWith('[') && name.endsWith(']')) {
+      const boundSyntax = boundEvent.sourceSpan.toString();
+      const expectedBoundSyntax = boundSyntax.replace(`(${name})`, `[(${name.slice(1, -1)})]`);
+      this.diagnostics.push(
+          this.ctx.templateTypeChecker.makeTemplateDiagnostic<ErrorCode.INVALID_BANANA_IN_BOX>(
+              this.ctx.component, boundEvent.sourceSpan, ts.DiagnosticCategory.Warning,
+              ErrorCode.INVALID_BANANA_IN_BOX,
+              `In the two-way binding syntax the parentheses should be inside the brackets, ex. '${
+                  expectedBoundSyntax}'. 
+                Find more at https://angular.io/guide/two-way-binding`));
+    }
+  }
+
+  getDiagnostics(template: TmplAstNode[]): ts.Diagnostic[] {
+    this.diagnostics = [];
+    for (const node of template) {
+      node.visit(this);
+    }
+    return this.diagnostics;
+  }
+}