From 6ba68a5ae6094748d378550039a215666d1fbd0a Mon Sep 17 00:00:00 2001
From: Lukas Taegert-Atkinson <lukas.taegert-atkinson@tngtech.com>
Date: Tue, 8 Sep 2020 06:50:13 +0200
Subject: [PATCH] Handle debugger statements as if-statement branches

---
 CHANGELOG.md                                       |  9 +++++++++
 src/ast/nodes/IfStatement.ts                       | 14 ++++----------
 test/function/samples/unknown-statement/_config.js |  3 +++
 test/function/samples/unknown-statement/main.js    |  4 ++++
 4 files changed, 20 insertions(+), 10 deletions(-)
 create mode 100644 test/function/samples/unknown-statement/_config.js
 create mode 100644 test/function/samples/unknown-statement/main.js

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7bbcf57b5aa..72099eac8aa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,14 @@
 # rollup changelog
 
+## 2.26.11
+*2020-09-08*
+
+### Bug Fixes
+* Do not fail for unknown nodes as if statement branches (#3769)
+
+### Pull Requests
+* [#3769](https://github.com/rollup/rollup/pull/3769): Handle debugger statements as if-statement branches (@lukastaegert)
+
 ## 2.26.10
 *2020-09-04*
 
diff --git a/src/ast/nodes/IfStatement.ts b/src/ast/nodes/IfStatement.ts
index b828353f53a..2fb3510d33d 100644
--- a/src/ast/nodes/IfStatement.ts
+++ b/src/ast/nodes/IfStatement.ts
@@ -70,18 +70,12 @@ export default class IfStatement extends StatementBase implements DeoptimizableE
 
 	parseNode(esTreeNode: GenericEsTreeNode) {
 		this.consequentScope = new TrackingScope(this.scope);
-		this.consequent = new this.context.nodeConstructors[esTreeNode.consequent.type](
-			esTreeNode.consequent,
-			this,
-			this.consequentScope
-		);
+		this.consequent = new (this.context.nodeConstructors[esTreeNode.consequent.type] ||
+			this.context.nodeConstructors.UnknownNode)(esTreeNode.consequent, this, this.consequentScope);
 		if (esTreeNode.alternate) {
 			this.alternateScope = new TrackingScope(this.scope);
-			this.alternate = new this.context.nodeConstructors[esTreeNode.alternate.type](
-				esTreeNode.alternate,
-				this,
-				this.alternateScope
-			);
+			this.alternate = new (this.context.nodeConstructors[esTreeNode.alternate.type] ||
+				this.context.nodeConstructors.UnknownNode)(esTreeNode.alternate, this, this.alternateScope);
 		}
 		super.parseNode(esTreeNode);
 	}
diff --git a/test/function/samples/unknown-statement/_config.js b/test/function/samples/unknown-statement/_config.js
new file mode 100644
index 00000000000..b52eca19457
--- /dev/null
+++ b/test/function/samples/unknown-statement/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'handles unknown statements'
+};
diff --git a/test/function/samples/unknown-statement/main.js b/test/function/samples/unknown-statement/main.js
new file mode 100644
index 00000000000..2ef5c938b85
--- /dev/null
+++ b/test/function/samples/unknown-statement/main.js
@@ -0,0 +1,4 @@
+debugger;
+
+if (true) debugger;
+else debugger;