From 4fc5f6a5ff4f4894cb2868b952e9c7e55685a951 Mon Sep 17 00:00:00 2001 From: Anders Hejlsberg Date: Fri, 31 May 2019 16:40:22 -0700 Subject: [PATCH] When binding pattern contextually types x || y, x contextually types y --- src/compiler/checker.ts | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts index 5814b2dcfbf..bf83323741e 100644 --- a/src/compiler/checker.ts +++ b/src/compiler/checker.ts @@ -18435,11 +18435,13 @@ namespace ts { } return contextSensitive === true ? getTypeOfExpression(left) : contextSensitive; case SyntaxKind.BarBarToken: - // When an || expression has a contextual type, the operands are contextually typed by that type. When an || - // expression has no contextual type, the right operand is contextually typed by the type of the left operand, - // except for the special case of Javascript declarations of the form `namespace.prop = namespace.prop || {}` + // When an || expression has a contextual type, the operands are contextually typed by that type, except + // when that type originates in a binding pattern, the right operand is contextually typed by the type of + // the left operand. When an || expression has no contextual type, the right operand is contextually typed + // by the type of the left operand, except for the special case of Javascript declarations of the form + // `namespace.prop = namespace.prop || {}`. const type = getContextualType(binaryExpression, contextFlags); - return !type && node === right && !isDefaultedExpandoInitializer(binaryExpression) ? + return node === right && (type && type.pattern || !type && !isDefaultedExpandoInitializer(binaryExpression)) ? getTypeOfExpression(left) : type; case SyntaxKind.AmpersandAmpersandToken: case SyntaxKind.CommaToken: